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BSCCHBSCCH 202, , B. Sc. II YEAR, ORGANIC CHEMISTRY-II, CHEMISTRY, , SCHOOL OF SCIENCES, DEPARTMENT OF CHEMISTRY, UTTARAKHAND OPEN UNIVERSITY
Page 2 : BSCCH-202, , ORGANIC CHEMISTRY-II, , SCHOOL OF SCIENCES, DEPARTMENT OF CHEMISTRY, UTTARAKHAND OPEN UNIVERSITY, , Phone No. 05946-261122, 261123, Toll free No. 18001804025, Fax No. 05946-264232, E. mail
[email protected], htpp://uou.ac.in
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Course Editor, Prof. Om Prakash, Department of Chemistry, College of basic Sciences and Humanities, G.B. Pant University of Agriculture & Technology, Pantnager, Title, ISBN No., Copyright, Edition, Published by, , :, :, :, :, , Organic Chemistry- II, Uttarakhand Open University, 2018, , : Uttarakhand Open University, Haldwani, Nainital- 263139
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CONTENTS, , BLOCK- 1 DERIVATIVES OF HYDROCARBONS-I, , Unit -1 Alcohols, , 1-40, , Unit -2 Phenols, , 41-70, , Unit -3 Ethers and epoxides, , 71-90, , BLOCK-2 DERIVATIVES OF HYDROCARBONS-II, , Unit -4 Aldehydes, , 91-137, , Unit -5 Ketons, , 138-179, , Unit -6 Carboxylic acids, , 180-228, , Unit -7 Functional Derivatives of Monocarboxylic Acids, , 229-261, , BLOCK-3 NITRO COMPOUNDS, ORGANOSULPHUR AND ORGANO, PHOSPHORUS, , Unit -8 Organic Compounds of Nitrogen (Nitro compounds), Unit 9 Amino Compounds, Unit -10 Organosulphur and Organo Phosphorus Compounds, , 262- 290, 291-330, 331- 361
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT - 1 ALCOHOL, CONTENTS:, 1.1 Objectives, 1.2 Introduction, 1.3 Classification of alcohols, 1.4 Nomenclature of alcohols, 1.5 Methods of preparation of alcohols, 1.6 Acidic nature of alcohols, 1.7 Chemical reactions of alcohols, 1.8 Dihydric alcohols, 1.9 Methods of preparation, 1.10 Physical properties of dihydric alcohols, 1.11 Chemical reactions of vicinal glycols, 1.12 Trihydric alcohols, 1.13 Metods of preparation, 1.14 Chemical reactions, 1.15 Summary, 1.16 Terminal questions, 1.17 Answers (MCQs), 1.18 References, , UTTARAKHAND OPEN UNIVERSITY, , Page 1
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 1.1 OBJECTIVES, Objectives of this unit are to study the alcohols, their structures, nomenclature,, and classification on the basis of number of –OH groups present like monohydric, alcohol, dihydric and polyhydric alcohols. Classification on the basis of nature of, carbon attached with –OH group like primary, secondary and tertiary alcohols. This unit, also aims on methods of preparation of alcohols with their physical and chemical, properties, acidic and basic characters. Chemical reactions of alcohols like Acidcatalyseddehydration etc, Study on chemical properties of dihydric and polyhydric, alcohos have also been aimed in this unit, , 1.2 INTRODUCTION, Alcohols are organic compounds in which one or more hydrogen atoms from, hydrocarbon have been replaced by hydroxyl (-OH) group. They are some of the most, common and useful compounds in nature, in industry, and around the house. The, general formula for a simple acyclic alcohol is CnH2n+1OH, where n=1, 2, 3, etc. The, saturated carbon chain is often designated by the symbol R, so that ROH can represent, any alcohol in the homologous series. Alcohols can be viewed as organic analogues of, water in which one hydrogen atom is replaced by an alkyl group. The simplest and most, commonly used alcohols are methanol and ethanol. They occur widely in nature and, have many industrial and pharmaceutical applications., , OH, OH, CH3OH, , CH3CH2OH, , methanol, , ethanol, , OH, CH3CH2, , cyclopropanol, , cyclohexanol, , CH CH3, , isobutanol, , Aromatic compounds, which contain a hydroxy group on a side chain, behave like, alcohols are called aromatic alcohol. In these alcohols, the —OH group is attached to a, sp3 hybridised carbon atom next to an aromatic ring., , UTTARAKHAND OPEN UNIVERSITY, , Page 2
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ORGANIC CHEMISTRY-II, CH2OH, , BCHCH-202, , CH2CH2OH, , benzyl alcohol, , 2-, , phenyl ethanol, , CH2CH2CH2OH, , 3-, , phenyl propanol, , In some alcohols, the —OH group is attached to a sp3 hybridised carbon next to the, carbon-carbon double bond that is to an allylic carbon are known as allylic alcohols. In, some alcohols —OH group bonded to a carbon-carbon double bond i.e., to a vinylic, carbon or to an aryl carbon. These alcohols are also known as vinylic alcohols. Allylic, and benzylic alcohols may be primary, secondary or tertiary in nature., , CH2, , CH OH, , vinylic alcohol, , OH, CH2, , CH CH2 OH, , allylic alcohol, phenol, , 1.3 CLASSIFICATION OF ALCOHOLS, Alcohols are classified into following types on the basis of number of –OH groups, present in the molecule and nature of carbon attached with –OH group as follow:, (a) Monohydric Alcohols: These compounds contain only one –OH group., CH3CH2OH, , CH3CH2CH 2OH, , (b) Dihydric Alcohols: These contain two –OH groups., , CH2, , OH, , CH2, , OH, , (c) Trihydric Alcohols: These contain three –OH groups., CH2, CH, CH2, , OH, OH, OH, , UTTARAKHAND OPEN UNIVERSITY, , Page 3
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ORGANIC CHEMISTRY-II, , On the basis of nature of carbon atom attached with -OH group, , BCHCH-202, , the mnohydric, , Alcohols can be further classified as primary (1°), secondary (2°), or tertiary (3°), depending on the number of carbon atoms bound to the hydroxyl-bearing carbon., (a) Primary alcohol (1° alcohol): A primary alcohol has one alkyl group attached to, , the carbon bound to the –OH, i.e., a compound in which the hydroxyl group is, bounded to a primary carbon. Primary alcohols have the group –CH2OH, where the, carbon atom with the alcoholic hydroxyl group has at least two additional hydrogen, attached to that carbon. Primary alcohol has –OH group bonded to a carbon which is, bonded to one other carbon:, , H, , H, , H, , C, , C, , H, , H, , OH, , (b) Secondary alcohol (2° alcohol): A secondary alcohol has two alkyl group attached, , to the carbon bound to the –OH, i.e., the hydroxyl group is bounded to a secondary, carbon. Secondary alcohols have the group –CHOH, where the carbon atom with, the alcoholic hydroxyl group has only one additional H atom attached to it. There, are two R groups (R stands for any other organic chain or group), and the alcoholic, hydroxyl group is attached to a secondary carbon. Secondary alcohol has –OH, group bonded to a carbon which is bonded to two other carbon:, , H, , H, , OH, , H, , C, , C, , C, , H, , H, , H, , H, , (c) Tertiary alcohol (3° alcohol): A tertiary alcohol has three alkyl group attached to, , the carbon bound to the –OH, i.e., the hydroxyl group is bounded to a tertiary, carbon. Tertiary alcohols have the group –COH, where the carbon atom with the, alcoholic hydroxyl group has no additional H atoms attached to it., , UTTARAKHAND OPEN UNIVERSITY, , Page 4
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ORGANIC CHEMISTRY-II, H, , CH3, , H, , C, , C, , C, , H, , BCHCH-202, , H, , H, OH H, If we replace hydrogen with a –OH group we get the following groups for three, , alcohols:, , CH2OH, , CH OH, , primary alcohol, , C OH, , secondary alcohol, , tertiary alcohol, , OH, OH, , OH, OH, primary alcohol, , CH3, , CH2, , CH, , CH3, , CH3, , CH2, , C, , CH3, , CH3, secondary alcohol, , secondary alcohol, , tertiary alcohol, , 1.4 NOMENCLATURE OF ALCOHOLS, According to the IUPAC system of nomenclature, alcohols are called alkanols., They are named as the derivatives of the corresponding alkane in which the -e of the, alkane is replaced by -ol. The IUPAC have come up with a set of rules that are used to, name any alcohol regardless of its complexity. These rules are summarized as follows:, Step 1. Name the longest continuous chain to which the hydroxyl (—OH) group is, attached. Count the number of carbon atoms and identify the corresponding alkane. The, name for this chain is obtained by dropping the final -e from the name of the, hydrocarbon parent name and adding the ending -ol., Step 2. Number the longest chain to give the lowest possible number to the carbon, bearing the hydroxyl group., Step 3. Locate the position of the hydroxyl group by the number of the carbon to which, it is attached., Step 4. Number the any other substituents according to their position on the chain., , UTTARAKHAND OPEN UNIVERSITY, , Page 5
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 1.5 METHOD OF PREPARATION OF ALCOHOLS, The following methods are used for the preparation of alcohols:, , 1. Hydrolysis of haloalkanes: Haloalkanes can be converted to corresponding, alcohols using aqueous NaOH, KOH or Ca (OH)2. With this method primary and, secondary alcohols are formed from a primary and secondary halogenoalkanes. This, is a type of nucleophilic substitution reaction (SN). This reaction is useful only with, reactants that do not undergo E2 elimination readily., , RX, , +, , OH, , CH3CH2CH2Br, , H2O, , +, , ROH, , NaOH(aq), , +, , X, , H2O, , UTTARAKHAND OPEN UNIVERSITY, , CH3CH2CH2OH, , +, , NaCl, , Page 7
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. Reduction of carbonyl compounds: Carbonyl compounds (which contain –C–O, group) such as aldehydes, ketones, carboxylic acids and esters can be reduced to, alcohols. Aldehydes give primary alcohols while ketones yield secondary alcohols,, either by catalytic hydrogenation or by use of chemical reducing agents like lithium, aluminum hydride, LiAlH4. Carboxylic acids and esters also give primary alcohols, on reduction with hydride reagents such as LiAIH4 and sodium borohydride, , (NaBH4). NaBH4 does not reduce carbon-carbon double bonds, not even those, conjugated with carbonyl groups, and in thus useful for the reduction of such, unsaturated carbonyl compounds to unsaturated alcohols., , In the above reactions it is observed that only the carbonyl group is reduced and, the other functional groups remain unaffected. Highly selective behaviour of, , UTTARAKHAND OPEN UNIVERSITY, , Page 8
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ORGANIC CHEMISTRY, CHEMISTRY-II, (b) By reaction with esters:, , BCHCH, BCHCH-202, , Produces tertiary alcohols in which two of the, , substituents on the hydroxyl, hydroxyl- bearing carbon are derived from the Grignard reagent., , O, C OCH2CH3, , M, MgBr, NH4+, , C OH, , (c) By reaction with epoxides: Grignard reagents react with epoxide to yield primary, alcohols containing two or more carbon atoms., , UTTARAKHAND OPEN UNIVERSITY, , Page 11
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 5. Fermentation: Ethanol is prepared on a large scale using fermentation process. It, involves breaking down large molecules into simpler ones using enzymes. Usually,, yeast is added as a source of enzymes. Yeast converts the reactant glucose or, fructose into ethanol and carbon dioxide in presence of zymase enzyme., , 1.6 ACIDIC NATURE OF ALCOHOLS, Alcohols can act as Brönsted acids as well as Lewis base due to donation of, proton and presence of unpaired electron on oxygen respectively. Alcohols are very, weak acids because the alkyl group pushes electrons towards the —OH group, so that, the oxygen does not strongly attract the electrons in the —OH bond. Furthermore once, a RO- ion is formed, it cannot be stabilized by the delocalization of the charge. Thus, alcohols react only to a very slight extent with alkali, but will react with very, electropositive metals under anhydrous conditions to give alkoxide with the general, formula RO- M+., Example: Reaction of ethanol with sodium, 2CH3CH2OH +, , 2Na , , 2CH3CH2O- Na+, , +, , H2, , Addition of water will regenerate the alcohol readily., CH3CH2O-Na+ +, , H2 O , , CH3CH2OH, , + NaOH, , The reaction is much slower than the reaction of water with sodium. Alcohols tend to be, slightly less acidic (pKa = 15) compared to water (pKa = 14). The higher the pKa value, the lower is the acid strength. The reaction of alcohol with sodium can be used to, deposite the excess sodium in the laboratory. Even alcohols are neutral to litmus and do, not reacts with alkali like NaOH but contain active hydrogen atom so reacts with Na or, K metal., , UTTARAKHAND OPEN UNIVERSITY, , Page 12
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ORGANIC CHEMISTRY-II, , BCHCH-202, , CH3CH2OH + NaOH No reaction, Reactivity of alcohol towards metal: 1° > 2° > 3° alcohol. An electron-releasing group, (-CH3, -C2H5) increases electron density on oxygen tend to decrease the polarity of O-H, bond. For example, with methanol:, H+, , +, , CH3 ONa, Sod., methoxide, , NaOH, Strong, base, , CH3 OH, Methanol, , H2SO4, Strong, acid, , +, , CH3 OH2, Protonated, methanol, , (i) The lower alcohols are colourless liquids with a characteristic smell and a burning, taste. The higher members (with more than 12 carbons) are colourless wax like solids., (ii) Because of hydrogen bonding, alcohols tend to have higher boiling points than, comparable hydrocarbons and ethers of similar molecular weight. Alcohols exists, associated molecules due to the association of molecules in the liquid phase through, strong intermolecular hydrogen bond between hydrogen atom of one molecule and, oxygen atom of another molecule. The oxygen-hydrogen bond is polar because oxygen, is much more electronegative than hydrogen. The lowers members have low boiling, points. With the increase in molecular weight, the boiling points keep on increasing, gradually. For example, the boiling point of butyl alcohol is 118°C whereas the boiling, point of the isomeric diethyl ether is 36°C., (iii) Solubility: The general rule in solubility is “like dissolves like.” The hydroxyl, group generally makes the alcohol molecule polar and therefore more likely to be, soluble in water. Hydrogen bonding also has an effect on water solubility. The OH, groups of an alcohol can hydrogen bond with water, and so this portion of the alcohol is, hydrophilic. On the other hand, the alkyl chain in an alcohol is similar to hydrophobic, molecules like hydrocarbon that do not mix with water. Compounds like alcohols that, have hydrophilic and hydrophobic regions are called ambiphilic (or amphiphilic). The, water solubility of a given alcohol depends on whether the hydrophilic OH or the, hydrophobic, , alkyl, , chain, , dominates., , Alcohols, , with, , shorter, , carbon, , chains, , (CH3OH,CH3CH2OH, CH3CH2CH2OH) are usually more soluble than those with longer, carbon chains because the increasing size of the nonpolar chain disrupts the hydrogen, bonding network. Formation of hydrogen bonds with water will increase their, , UTTARAKHAND OPEN UNIVERSITY, , Page 13
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ORGANIC CHEMISTRY-II, , BCHCH-202, , solubility. That is why alcohols are much more soluble in water than their, corresponding alkanes, aromatic hydrocarbons, alkyl halides or aryl halides. Amongst, isomeric alcohols, the solubility increases with branching., (iv)The B.P. and M.P. will also increase with carbon chain length. The longer the, alcohols carbon chain, the better the chance that the alcohol will be a solid at room, temperature. Alcohols show higher boiling points than alkane and ethers of similar mass, due to hydrogen bonding. Since there is not any possibility of hydrogen bonding in, ether, the forces between the ether molecules are much weaker and can be much more, easily vaporized., , CH3CH2CH2CH2CH2CH2CH2CH2OH, CH3CH2OH, , Insoluble in water, , Soluble in water, O, , H, , O, , H, , H, , O, H, , H3 C, , H, , R, , O, , R, , R, , O, , H ..... O, , H ..... OH, , H, , H, , Comparison of boiling points among isomeric alcohols, , CH3, CH3CH2CH2CH2OH, 1_ butanol, , B.P., , 2_, , 118 0, , M.Wt =, , CH3, , C, , 74, , CH3, , CH CH2OH, , methyl 1 _ propanol, B.P., , 108, , M.Wt =, , 0, , C, , 74, , CH3, , C OH, , CH3, _, 2 methyl 2 _ propanol, B.P., , 83, , 0, , C, , M.Wt = 74, , (v) The viscosity of small alcohols is much higher than the viscosity of alkanes., (vi) Generally alcohols are lighter than water, i.e., less dense than water. Density of, alcohols increases with molecular mass., , UTTARAKHAND OPEN UNIVERSITY, , Page 14
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 1.7 CHEMICAL REACTIONS OF ALCOHOLS, Alcohols acts both as nucleophiles as well as electrophiles. The bond between OH is broken when alcohols react as nucleophiles and the bond between C-O is broken, when they react as electrophiles. The chemical properties of any given aliphatic alcohol, depend on the nature of the alkyl group and on the properties of the hydroxyl group., Based on the cleavage of O-H and C-OH bonds, the reactions of alcohols may be, divided into two groups:, (A) Reactions involving cleavage of O-H bond, 1. Acylation of alcohol: When alcohol reacts with acylhalide and anhydride, , substitution of hydrogen atom by acyl group is known as acylation of alcohols., ROH, , +, , CH3COCl, , ROH, , +, , (CH3CO)2O, , ROCOCH3, , +, , HCl, , ROCOCH3 + CH3COOH, , (B) Reaction involving fission of R—OH bond (cleavage of C—O bond): The, reactions involving R – OH bond with cleavage of C – O bond are as follow, , 1. Dehydration: (a) Intramolecular dehydration (forming alkene): Alcohols, undergo dehydration to form unsaturated hydrocarbon on treating with a protic acid, e.g., con. H2SO4or H3PO4, or catalysts such as anhydrous ZnCl2or Al2O3. In this, reaction the OH and an H groups removes from an adjacent carbons. Since water is, removed from the alcohol, this reaction is known as a dehydration reaction (or an, , elimination reaction). Secondary and tertiary alcohols are dehydrated under much, milder conditions. The conditions for dehydrating alcohols depend closely on the, structure of individual alcohols., For primary alcohols, the conditions required are conc. sulphuric acid and temperature, of 1700C., , UTTARAKHAND OPEN UNIVERSITY, , Page 15
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ORGANIC CHEMISTRY, CHEMISTRY-II, , BCHCH, BCHCH-202, , The main function of the acid is to transform the poor leaving group —OH, OH into the very, v, good leaving group —OH2. The order of the relative ease of dehydration of alcohols is:, 3 0 > 20 > 10, , Tertiary carbocations are most stable and therefore are easier to form than secondary, and primary carbocations; tertiary alcohols are the easiest to deh, dehydrate., The order of stability of the carbocations is:, CH3, CH3, , C, , CH3, CH3, , CH3, , C, H, , CH3, , H, , H, , C, , H C, , H, , H, , Dehydration of secondary and tertiary alcohols containing more than three carbon, atoms will give a mixture of alkenes, the major product can be determined from, Satzeff’s Rule:, , Satzeff’s Rule— When an alkene is produced in an elimination reaction, the major, , product is the one with the more highly substituted double bond i.e., the major product, is that contains the higher number of alkyl groups attached to the C=C bond. e.g., , Rearrangement of the alkyl, , groups of alcohols is very common in dehydration, particularly in the presence of strong, acids, which are conducive to carbocation formation. Typical examples showing both, methyl and hydrogen migration follow:, , Mechanism:, , UTTARAKHAND OPEN UNIVERSITY, , Page 17
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ORGANIC CHEMISTRY, CHEMISTRY-II, , BCHCH, BCHCH-202, , (b), Intermolecular dehydration, ydration (forming ether):, When the dehydration is carried out at a temperature of 1400C with an excess of alcohol, ether will be formed. This reaction removes a molecule of water from two alcohol, molecules, causing the two “R” groups to become attached to aann oxygen atom, forming, an ether functional group:, , 2, , CH3CH2OH, , Con.H, H2SO4, , CH3CH2, , O CH2CH3, , +, , H2O, , 2. Halogenation: Alcohols can be converted to alkyl halides using one of three, reactions:, , (a) Reaction with hydrogen halides: Respective alkyl halides are formed by reacting, with the appropriate hydrogen, hydrogen halide, HCl for chlorination, HBr for bromination, and, , HI for iodination. The reaction involves the initial protonation of the hydroxyl group of, the alcohol. This improves the leaving group ability of the hydroxyl group., , HCl, , R OH, , HBr, HI, , R Cl, , +, , H2O, , R, , Br, , +, , H2O, , R, , I, , +, , H2O, , Mechanism:, Step1: Protonation, tion of the alcohols: The alcohol acts as a weak base and accepts the, proton donated by the hydrogen halide., , UTTARAKHAND OPEN UNIVERSITY, , Page 18
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ORGANIC CHEMISTRY-II, +, , ROH, , H, , +, , R, , O, , BCHCH-202, +, , H, , H, , Step 2: Removal of a water molecule and formation of halide through SN2 mechanism/, SN1 mechanism as:, (i) For primary and secondary alcohols, it is a SN2 reaction., , R C H2, , X, , O, , +, , R-C H 2 -X, , H, , H, , (ii) For tertiary alcohols, it is a SN1 reaction., R, R3 C, , O, , +, , C, , H, , +, , R, , H, , R, , R, R, C, , X, , +, , R, , C, X, , R, , R, R, , (iii) Rate of the reaction for 10, 20 and 30 alcohols:, The order of rates of reaction:, 30 alcohol > 20 alcohol, , > 10 alcohol, , The rate can be shown by the turbidity in the aqueous layer since the chloroalkane, formed is immiscible with water., , (b) Reaction with thionyl chloride, SOCl2: Alcohols will react with thionyl chloride, to produce alkyl halides. The reaction involves a nucleophilic attack of the alcohol on a, SOCl2 molecule displacing one of the chlorides. Then the chloride will act as the, nucleophile in a second step and displace the oxygen from the carbinol carbon., , R OH, , +, , SOCl2, , R Cl, , +, , SO2, , +, , UTTARAKHAND OPEN UNIVERSITY, , HCl, , Page 19
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 3. Oxidation: Alcohols can be oxidized by various oxidizing agents to aldehyde,, ketones or carboxylic acids. Oxidation is the gain of oxygens and /or the loss of, hydrogens., , OH, , O, , [O], C, , C, oxidising agent, , H, , (a) 10 alcohol oxidizes readily, first to an aldehyde, then to a carboxylic acid. These, two oxidation steps make sense because the primary alcohol functional group has two, C-H bonds that can be broken. Primary or secondary alcohols can be oxidized to, produce compounds containing the carbonyl group (a carbon-oxygen double bond,, C=O). Strong oxidizing agents such as hot alkaline KMnO4 or CrO3 in H2SO4 will, oxidize primary alcohols right past the aldehyde to the salt of the carboxylic acid in, which the acid may be precipitated by acidification. The alcohol, aldehyde and acid, retain the same number of carbon atoms., , O, , [O], , R C, , RCH2OH, , H, , H2O, , +, , oxidising agent, O, , [O], CH3CH2OH, , CH3, , C, , H, , +, , H2O, , oxidising agent, , [O], CH2OH, , O, C, , H, , oxidising agent, , b. 20 alcohol has only one C-H bond that can be broken, so it can only oxidize once, to, a ketone, which cannot be oxidized any further:, , UTTARAKHAND OPEN UNIVERSITY, , Page 21
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ORGANIC CHEMISTRY-II, H, R, , C OH, , R, _2, , R', , C O, , H, R', , 30 alcohol, , Ketone, , OH, CH3, , BCHCH-202, , CH CH3, , O, , [O], CH3, , C, , OH, , [O], CH3, , O, CH3, , C, , OH, , +, , H2O, , O, , [O], , +, , H2O, , c. 30 alcohol has no C-H bonds that can be broken, so it is not oxidized, no matter how, strong the oxidizing agent because it would involve the breakage of the high energy, C—C bonds in the alcohol molecule., , CH3, CH3, , C OH, , [O], , No oxidation product, , CH3, In acidic solutions, 30 alcohols can he oxidized to give a mixture of ketone and acid,, both with fewer carbon atoms than the alcohol., CH3, CH3, , C OH, , O, [O], , CH3, , C CH3, , +, , CH3COOH, , CH2CH3, , Characterization of the oxidation products of alcohols is a means of distinguishing, between primary, secondary and tertiary alcohols., , UTTARAKHAND OPEN UNIVERSITY, , Page 22
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ORGANIC CHEMISTRY-II, HO CH2, , CH2 OH, , H2SO4, , +, , HO CH2, , BCHCH-202, CH2, , CH2, , O, , CH2 OH, , O, CH2, , +, , 2, , H2O, , CH2, , Uses of ethylene glycol:1. It is used as antifreeze substance which prevents the freezing of water in car, radiators in cold countries., 2. Due it has a high viscosity, so it is used in the hydrolic break , printing ink ball, pen, inks, organic solvents ., 3. Used in the manufacture of Dacron, dioxane etc., 4. As a solvent and as a preservatives., 5. As a cooling agent in aeroplanes., 6. As an explosives in the form of dinitrate., 7. Large amounts of ethylene glycol are converted to polymers ( such as polyethylene, glycol ) used in The manufacture of dacron fibers ,photographic films and cassette, tapes., , 1.12 TRIHYDRIC ALCOHOL, It is a triol. The introduction of third –OH group in diol molecule raises the b.p. about, 1000C, increase viscosity and make the alcohol more sweet. Viz; glycerol, CH2OH, CHOH, CH2OH, , It is desigbated as prop-1, 2, 3-triol in IUPAC nomenclature. It may be considered as, derivative of propane, obtained by replacement of three hydrogen atoms from different, , UTTARAKHAND OPEN UNIVERSITY, , Page 28
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ORGANIC CHEMISTRY-II, , BCHCH-202, , carbon atoms by three hydroxyl group. In industry, it’s known as glycerine. It occurs as, glycosides in almost all animal and vegetable oils and fats., , 1.13 METHODS OF PREPARATION, Glycerol can be synthesized by following different methods:, 1. From fats and oil: On hydrolysis of fats and oils, glycerol and higher fatty acids, are formed., , CH2OOCR, , CH2OH, , CHOOCR, , +, , 3 H2O, , CHOH, , CH2OOCR, , +, , 3 RCOOH, , CH2OH, , 2. By fermentation of sugars: Alcoholic fermentation of sugar in the presence of, sodium sulphite gives good yield of glycerol., CH2OH, , yeat, , C6H12O6, , CHOH, , Na2SO2, , 3., , +, , CH3CHO, , +, , CO2, , CH2OH, Synthesis (from propene): Today much of glycerol is obtained from propene., , CH3, , Cl2, , CH, , 600 0C, , CH2, , CH2Cl, CH, , dil NaOH, , CH2, , CH2OH, , CH2OH, HOCl, , CH, , CHCl, , dil NaOH, , CH2OH, , CH2, , CH2, , OH, , CH OH, CH2 OH, , Physical properties: Glycerol is a colourless, odourless, viscous and hygroscopic, liquid,, It, , is, , sweet, soluble, , in, in, , water, , taste, and, , and, ethyl, , alcohol, , non-oxic, but, , in, , insoluble, , nature., in, , ether., , It has high boiling point, i.e., 290°C. The high viscosity and high boiling point of, glycerol are due to association through hydrogen bonding purified in the lab by reduced, pressure distillation or vacuum distillation., , 1.14 CHEMICAL REACTIONS, Glycerol molecule contains two 10 – OH groups and one 20 – OH group. Thus, it shows, characteristics of both primary and secondary alcohols., , UTTARAKHAND OPEN UNIVERSITY, , Page 29
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Uses: Glycerol is used: Glycerol is used as a sweetening agent in confectionery,, , beverages and medicines being non-toxic in nature. It is used as antifreeze in, automobile radiators, in the preparation of good quality of soap, hand lotions, shaving, creams, tooth pastes and cosmetics and as a lubricant in watches and preservative., , 1.15 SUMMARY, In this unit we have learnt that: Alcohols are compounds in which a hydrogen of alkane, has been replaced by an –OH group and are classified as, , monohydric, dihydric,, , trihydric or polyhydric on the basis of –OH group present. The monohydric alcohols, can be classified into 1o, 2o and 3o alcohols. In IUPAC name alcohols are designated as, alkannol by replacing ‘e’ with –ol from the corresponding alkane. This unit also, describes the methods of preparation of alcohols by using different methods like;, hydrolysis of halogenoalkanes,hydration of alkene, reduction of aldehydes and ketones, using Grignard reagents(RMgX), LiAlH4, NaBH4,by fermentation of carbohydrates etc., The amphoteric nature of alcohols has also been described in this unit. As an acid, it, ionizes to form an alkoxide ion (RO-) and hydrogen ion, H + in the presence of a base,, while in, , presence of an acid, the alcohol may function as a base and can accept a, , proton. This unit, , makes the readers aware about methods of preparation, physical, , properties and chemical reactions along with applications of dihydric alcohol glycol and, trihydric alcohol glycerol., , 1.16 TERMINAL QUESTION, Q. 1. Explain why Alcohols are acidic in nature., Q. 2. Write the mechanism of dehydration of ethyl alcohol with conc. H2SO4., Q. 3.Why boiling point of alcohols is higher than that of alkanes of corresponding, molecular weight., Q. 4., , Explain why polarity of primary alcohol is maximum?Q.5.Write the major, , product(s), CH3, HO, H, , CH2CH3, , of, , the, , following, , reaction., , SOCl2, pyridine, , UTTARAKHAND OPEN UNIVERSITY, , Page 34
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ORGANIC CHEMISTRY-II, CH2OH, , CH2OH, , BCHCH-202, , PBr3, , CrO3, H2SO4, , OH, , PBr3, , Q.6. Write short note on:1. Satuzaff’s rule, 2. Glyptal, 3. Amphoteric nature of alcohols, 4. Synthesis of glycerol, 5. Applicatoions of glycol and glycerol, 6. Classification of monohydric alcohols, 7. Oxidation of glycol and glycerol, Q.8. Tick the appropriate option (MCQs), 1. Ethanol containing some methanol is called, A. Absolute sprit, , B. Rectified sprit, , C. Power alcohol, , D. Methylated sprit, , 2. Glycerol is a:, A. Primary alcohol, , B. Monohydric alcohol, , C. Secondary alcohol, , D. Trihydric alcohol, , 3. Which of the following can work as a dehydrating agent for alcohols?, A.H2SO4, , B.Al2O3, , UTTARAKHAND OPEN UNIVERSITY, , Page 35
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ORGANIC CHEMISTRY-II, C.H3PO4, , BCHCH-202, D. All., , 4. Primary and secondary alcohols on action of red hot copper give, A. Aldehydes and ketons respectively, , B.Ketones and aldehydes respectively, , C. Only aldehydes, , D.Only ketones, , 5. Which one has highest boiling point?, A. Butan-2-ol, , B.Ethane, , C.Butane, , D.Pentane, , 6. Which of the following has maximum hydrogen bonding?, A. Ethyl amine, , B.Ammonia, , C. Ethyl alcohol, , D.Diethyl ether, , 7. What is the product of the following reaction?, O, , H2, Pt, A.Cyclohexanol, , B.Cyclohexane, , C. Cyclohexene, , D. 1,2-cyclohexanediol, , 8. What is the product of the following reaction?, O, , (i) L iA lH 4, ?, (ii) H 2 O, , O, , OH, A., , B., , OH, C., , D., , UTTARAKHAND OPEN UNIVERSITY, , Page 36
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ORGANIC CHEMISTRY-II, , BCHCH-202, , A. cis-3-methylcyclohexanol, , B. cis-5-methylcyclohexanol, , C. trans-3-methylcyclohexanol, , D. trans-5-methylcyclohexanol, , 13. Identify the tertiary alcohol., , OH, B., , A., OH, , OH, OH, , OH, D., , C., , OH, 14. What is the hybridization of the oxygen atom in alcohols?, A. sp, , B. sp2, , C. sp3, , D. sp3d, , 15. The compound found in Whisky, Brandy & Bear:, A. CH3OH, , B. CH3CH2OH, , C. CH3CH2CH2OH, , D. CH3CH2CH2CH2OH, , 16. Which of these five-carbon alcohols would you expect to be most water soluble?, , OH, A., , C., , OH, , OH, , B., , C, , D., , OH, , 17. Which is the major product of the following reaction?, , UTTARAKHAND OPEN UNIVERSITY, , Page 38
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ORGANIC CHEMISTRY-II, , BCHCH-202, , A. Nitroderivative of glycerol, , B. Nitro derivative of glycol, , C. Acetyl derivative of glycerol, , D. Acetyl derivative of glycol, , 1.17 ANSWERS(MCQs):, 2.D, , 2.D, , 3.D, , 4.A, , 5.A, , 6.C, , 7.C, , 8.C, , 9.C, , 10.A, , 11.D, , 12.C, , 13.D, , 14.C, , 15.B, , 16.B, , 17.B, , 18.A, , 19B, , 20.B, , 1.18 REFERENCES, 1. Jerry march, Advanced Organic Chemistry, 4th edition, Wiley India, 2010., 2. P.S. Kalsi, Organic Reactions and their Mechanisms, 2nd edition, New age, International Publishers. 2017, 3. S.M. Mukherji and S.P. Singh, Reaction Mechanism in Organic Chemistry. Trinity, Press, 2016, 4. Goutam Brahmachari, Organic name Reactions, Narosa publishing house, New, Delhi. Revised version: 2012., 5. I.L. Finar, Organic Chemistry, Vol. II. 5th edition, ELBS & Longman group Ltd.,, 1974., 6. Organic chemistry, R.T.Morrision and R.N.Boyd, 6th edition, Prentice Hall Private, Ltd. 1997., 8. Advanced Organic Chemistry, F.A. Carey and R.J. Sundberg, Plenum. 5th Edition,, 2007, 9. B.S Bahal and Arun Bahal Advanced Organic Chemistry,1993,, Company Ltd. Ram Nagar, new Delhi, , UTTARAKHAND OPEN UNIVERSITY, , S. Chand &, , Page 40
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT -2 PHENOLS, CONTENTS:, , 2.1 Objectives, 2.2 Introduction, 2.3 Nomenclature, 2.4 Methods of preparation of phenols, 2.5 Commercial preparation of phenols, 2.6 Physical properties of phenols, 2.7 Acidic character of phenols, 2.8 Chenical reactions of phenols, 2.9 Substituted phenols, 2.10 Summary, 2.11 Terminal questions, 2.12 Answers (MCQs), 2.13 References, , OBJECTIVES, The objectives of this unit are to study the structure and bonding of phenol. To, study physical and chemical properties of phenols, their acidic characters. Besides these, objectives this unit will make aware the students about general methods of preparation of, phenols, comparative acidic characters with alcohols, various chemical reactions,, characteristic electrophilic substitution reactions and some name reactions involving, phenols., , UTTARAKHAND OPEN UNIVERSITY, , Page 41
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2.2 INTRODUCTION, Phenols are compounds in which the -OH group is directly attached to an, aromatic carbon like benzene ring. Although they share the same functional group with, alcohols, where the –OH group is attached to an aliphatic carbon, the chemistry of, phenols is very different from that of alcohols. The simplest phenol is hydroxybenzene, also called phenol with formula C6H5OH. Simple phenol is an antiseptic. A phenolic, compound hexachlorophene is a constituent of several mouthwashes, deodorant soaps, and medicinal skin cleansers., Cl, , OH, , Cl, Cl Cl, , Cl, Phenol, (hydroxy benzene), , Cl, OH, , OH, , hexachlorophene, , The –OH group consists of an O atom bonded to a sp2-hybridised aromatic C atom and, a H atom via σ bonds as follow. Both the C-O and the O-H bonds are polar due to the, high electronegativity of the O atom. Conjugation exists between an unshared electron, pair on the oxygen and the aromatic ring., This results in, compared to simple alcohols: - A shorter carbon-oxygen bond distance,, a more basic hydroxyl oxygen, a more acidic hydroxyl proton (-OH), , sp2, hybridized carbon, with one vacant p orbital, , O H, , vacant p orbitals, , OH, , C6H5OH, , Structure of phenol, , UTTARAKHAND OPEN UNIVERSITY, , Page 42
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ORGANIC CHEMISTRY-II, , BCHCH-202, , The electronic structure of phenol can be represented as resonance hybrid of the, following canonical forms., +, , .. H, O:, , :O, , H, , +, , :O, , H, , +, , :O, , .._, , H, , H, O, , _.., _.., IV, , III, , II, , I, , It must be noted that the aromatic compounds in which -OH group is not directly, attached to benzene ring are not phenols but are called aromatic alcohols. These may be, regarded as aryl derivatives of aliphatic alcohols., CH3, CH2OH, , CH3, , CH2CH2OH, , OH, , Benzyl alcohol, , 2-Phenylethanol, , 2-Phenylpropanol, , 2.3 NOMENCLATURES, Functional group suffix = -common - phenol, systematic - benzenol, Functional group prefix = hydroxy, The hydroxyl derivatives of toluene have been given the name CRESOLS. If a phenolic, moiety is included in a molecule which is named by IUPAC system, the –OH group is, specified as a substituent according to the order of precedence. In such a case a, substituent (COOH or –CHO) is assigned number-1. The systematic and common names, of some phenols have been illustred as follow., M O H O H Y D R IC P H E N O L S :, OH, , OH, , OH, , OH, CH3, , CH3, CH3, phenol, , 2-, , m eth y lp h en o l, , 3-, , m eth y lp h en o l, , UTTARAKHAND OPEN UNIVERSITY, , 4-, , m eth y lp h en o l, , Page 43
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ORGANIC CHEMISTRY-II, , BCHCH-202, , The cumene obtained from petroium as above is oxidised at 1300C in presence of metal, catalyst, which gives phenol as the ultimate product by envolving the intermediate, compounds in sequence as follow., CH3, H 3C, , CH3, , CH, , H 3C, O2, 130, , 0, , OH, , C O OH, , O, H+, , CH2, , +, , C CH3, , C cat., phenol, , hydroperoxide, , cumene, , acetone, , 2.6 PHYSICAL PROPERTIES OF PHENOLS, Phenol has higher boiling point than the arenes or haloarenes or ethers of same, molecular weight. It is due to the formation of intermolecular hydrogen bond.Pure, phenol is a white crystalline solid, smelling of disinfectant. It has to be handled with, great care because it causes immediate white blistering to the skin. The crystals are often, rather wet and discolored. Phenols are sparingly soluble in water but readily soluble in, organic solvents such as alcohol and ether. The boiling points of phenols increase with, increase in the number of carbon atoms (increase in van der Waals forces). The -OH, group in alcohols and phenols is involved in intermolecular hydrogen bonding which is, responsible for the high boiling point that is lacking in ethers and hydro carbons., H, , O, , H, , O, , H, , O, , H, , O, , H, , O, , H, , O, , 2.7 ACIDIC CHARACTER OF PHENOLS, Unlike alcohols (which also contain an -OH group) phenol is a strong acid. Phenols turn, blue litmus red and react with metals liberating hydrogen. Phenols behave as acids, because of the presence of more polar O-H group in them. They ionise in aqueous, solutions and give H+ ions to a base. However they do not react with carbonates or, bicarbonates., , UTTARAKHAND OPEN UNIVERSITY, , Page 48
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ORGANIC CHEMISTRY-II, , BCHCH-202, , The greater acidity of phenols can be attributed to the resonance stablisation of the, phenoxide ion formed after losing hydrogen ion. The delocalisation of the negative, charge over the benzene ring stabilises the phenoxide ion. No such stabilisation is, possible, in case of alkoxide ions. Phenol is a very weak acid than carboxylic acid and, the position of equilibrium lies well to the left., .., :OH, , .., :O, +, , H2O, , H3O, , +, , phenol, , phenoxide ion, , Phenols as well as phenoxide ion both are resonance stabilised. The negative charge on, the oxygen atom is delocalised around the ring. The benzene ring helps to stabilise a, negative charge on the phenoxide ion, C6H5O–, and this makes phenol appreciably acidic, (unlike ethanol, which is neutral, a solution of phenol in water has a pH of about 5). The, more stable the ion is, the more likely it is to form. Phenol reacts with aq. sodium, hydroxide solution to give a colourless solution containing sodium phenoxide., .., OH, .., , +, , NaOH, , .., O, .., , ONa, , phenol, , sod. phenoxide, , +, , Na+, , phenoxide ion, , The various contributing structures of phenol and phenoxide ion are given below:, +, , .. H, O:, , :O, , H, , +, , :O, , H, , +, , :O, , .._, , H, , H, , O, , _.., _.., , I, Phenol, .., O:, , II, , III, , IV, , V, , :O :, , :O :, , :O :, , O, , .._, , _.., _.., , I, Phenoxide ion, , II, , III, , UTTARAKHAND OPEN UNIVERSITY, , IV, , V, , Page 49
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Comparative acidic character of alcohols and phenols, The ionisation of an alcohol and a phenol takes place as shown in equation:, R OH, ionization of alcohol, OH, , RO, , +, , H, , alkoxide, .., :O, +, , H, , ionization of phenol phenoxide, , In alkoxide ion, the negative charge is localised on oxygen while in phenoxide ion, the, charge is delocalised. The delocalisation of negative charge (structures I-V) makes, phenoxide ion more stable and favours the ionisation of phenol. The hydroxyl group, in, phenol is directly attached to the sp2 hybridised carbon of benzene ring which acts as an, electron withdrawing group. Due to this, the charge distribution in phenol molecule, as, depicted in its resonance structures, causes the oxygen of -OH group to be positive. A, compound in which hydroxyl group directly attached to an aromatic ring is more acidic, than the one in which hydroxyl group is attached to an alkyl group. Acids react with the, more reactive metals to give hydrogen gas. Alcohols and phenols react with active, metals like Na, K, Al etc to liberate hydrogen gas. The reactions of phenol with metals as, well as NaOH indicate it is relatively more acidic than alcohols and also water. The sp2, carbon of phenol attached to ‘O’ being more electronegative than sp3 carbon of alcohols,, it decreases the electron density on oxygen. Because of this oxygen develops still more, electron seeking character and releases proton by taking the shared pair of electrons with, it., , Effect of substituents on acidity of phenol: In substituted phenols, the presence of, electron withdrawing groups such as nitro group enhances the acidic strength of phenol., This effect is more pronounced when such a group is present at ortho and para positions., It is due to the effective delocalisation of negative charge in phenoxide ion.On the other, hand, electron releasing groups, such as alkyl groups, in general, do not favour the, , UTTARAKHAND OPEN UNIVERSITY, , Page 50
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ORGANIC CHEMISTRY-II, , BCHCH-202, , formation of phenoxide ion resulting in decrease in acid strength. Cresols, for example,, are less acidic than phenol., , OH, NO2, , OH, , OH, , NO2, , CH3, , NO2, , NO2, picric acid/TNP, , OH, , OH, , CH3, , NO2, less acidic, , more acidic, , Electron releasing groups like alkyl groups increase the electron density on oxygen and, decrease the polarity of O-H bond. This decreases the acidic strength. Hence, alkylphenols have greater pKa values as compared to phenol itself., On the other hand, electron withdrawing substituents increase the acidity and phenols, having these substituents (–Cl, –NO2, etc.) have lower pKa values than phenol. In fact,, 2,4,6-trinitrophenol / picric acid (TNP) is more acidic than many carboxylic acids., , 2.8 CHEMICAL REACTIONS OF PHENOLS, Alcohols and phenols both contain –OH group attached with carbon but in case of, phenols the carbon atom is member of phenyl ring as also shown above in resonating, structures in phenols the C-O bond acquires double bond character because of, delocalization of electrons from oxygen to phenyl ring, which results the C-O stronger, than O-H σ bond. The increased electron density in the phenyl ring activates it and gives, electrophilic substitution reaction., , Resists cleavage, .., O, , Resists cleavage, .., R O, .. H, , H, Easily cleaved, , Phenol, Resonance hybrid, , Alcohol, , UTTARAKHAND OPEN UNIVERSITY, , Page 51
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ORGANIC CHEMISTRY-II, , BCHCH-202, , In alcohols no resonance is possible and the non bonded electron pairs remain localized, on the oxygen atom. The C-O linkage thus retains its σ-bond character and is weak as, compared to that in phenol., Phenols thus undergo two types of reactions:, A. Reaction involving the –OH group, B. Reaction involving aromatic ring, A. Reactions involving –OH group:, 1. Aidic character: Phenols are acidic compared to alcohols as they furnish proton to, form phenoxide ion which is stabilized by resonance.Acidity of phenol is less than, carboxylic acids., , .., :O, , OH, , +, , ionization of phenol, , .., O:, , :O :, , H, , phenoxide, , :O :, , :O :, , .._, , O, _.., , _.., III, , II, , I, Phenoxide ion, , IV, , V, , Phenols when react with aq. NAOH or KOH (bot with Na2CO3) to form soluble sodium, salt known as phenoxides., , OH, , ONa, +, , NaOH, , 1, - - H2, 2, , UTTARAKHAND OPEN UNIVERSITY, , O, +, , Na+, , Page 52
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ORGANIC CHEMISTRY-II, , BCHCH-202, , B. Reactions involving aromatic ring: The aromatic ring in phenols generally undergo, electrophilic substitution reaction in which the hydroxyl group is a powerful activating, group and hence phenols readily undergo electrophilic substitution reactions. Phenol is, more reactive than benzene towards electrophilic reagents because there is an interaction, between the lone pairs on the oxygen atom in —OH or —O and the ring; which increase, the availability of electrons in the aromatic ring. Also, it directs the incoming group to, ortho and para positions in the ring as these positions become electron rich due to the, resonance effect caused by -OH group. In this reaction, an electrophile (electron loving, species) attacks the benzene ring and replaces one of its hydrogen atoms. Since the ortho, and para positions of the phenol are electron rich, the substitution takes place at these, positions., , O, O, , H, , H, , O, , E+, , H, , Ortho, , Ortho, , Meta, , Meta, Para, , Electophile attack at ortho and para positions, Common electrophilic aromatic substitution reactions taking place in phenol are as, follow:, , 1.Halogenation (Bromination): The -OH group in phenol can donate electrons back to, the delocalised π-system, helping to stabilise the intermediates of electrophilic, substitution and so making phenol much more reactive than benzene. It will react, immediately with bromine water, decolorising it and forming a white precipitate of, 2,4,6-tribromophenol. If bromine water is added to a solution of phenol in water, the, bromine water is decolourised and a white precipitate is formed. The usual halogenation, of benzene takes place in the presence of a Lewis acid, such as FeBr3, which polarises, the halogen molecule. The faster reaction in water is due to the presence of phenoxide, ions., , UTTARAKHAND OPEN UNIVERSITY, , Page 55
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ORGANIC CHEMISTRY-II, , BCHCH-202, , In case of phenol, the polarisation of bromine molecule takes place even in the absence, of Lewis acid., It is due to the highly activating effect of -OH group attached to the benzene, ring.Chlorine, in the absence of solvent, gives, , 2 and 4-chlorophenol. Bromine, in, , a nonpolar solvent (e.g. CS2 or CCl4) gives 2, 4-bromophenol., , OH, , OH, Br, +, , Br, , 3 Br, 2, , +, , 3, , HBr, , Br, phenol, , 2, 4, 6 - tribromophenol, , Bromination can be limited to monobromination to give mainly 4-bromophenol using, low temprature and less polar solvent such as carbon disulphide. The other product, formed in minor quantity is 2-bromophenol., , OH, , OH, , OH, Br, , CS2, +, , +, , Br2, , Br, , phenol, , 2. Nitration of Phenol: Phenol can be nitrated with dilute nitric acid. Monosubstituted, compound is obtained with dilute nitric acid at room temperature. Phenol reacts with, dilute nitric acid at room temperature to give a mixture of 2-nitrophenol and 4nitrophenol., , OH, dil.HNO3, phenol, , OH, , OH, NO2, +, , NO3, , UTTARAKHAND OPEN UNIVERSITY, , Page 56
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ORGANIC CHEMISTRY, CHEMISTRY-II, , BCHCH, BCHCH-202, , 4. Kolbe's reaction: On reaction sodium salt of phenol with carbon dioxide gas, ortho, hydroxy benzoic, enzoic acid is formed as the main product. The temperature is 400 K and a, pressure of 4-7, 7 atm is required. Sodium salicylates formed which an acidification yields, salicylic acid (ortho hydroxy benzoic acid)., OH, , OH, , ONa, +, , O, , CO2, , NaOH, , O, ONa, , sod. salicilate, , OH, CO, OOH, , salicylic acid, , 5. Fries Rearrangement: The Fries Rearrangement, rrangement enables the preparation of acyl, phenols. The reaction is catalyzed by Bronsted or Lewis acids such as HF, AlCl3, BF3,, TiCl4 or SnCl4. The acids are used in excess of the stoichiometric amount, especially the, Lewis acids, since they form complexes, complexes with both the starting materials and products., The reaction is ortho, para-selective, selective so that, for example, the site of acylation can be, regulated by the choice of temperature., O, , O, Lewis acid, , OH, , HO, +, , R, , R, O, , R, O, , Mechanism, , UTTARAKHAND OPEN UNIVERSITY, , Page 58
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Properties: White solid M.P. 1100C Turns gray in air, soluble in water, forms 2,4,6tribromoresorcinol when treated with bromine water. It couplesdiazonium salts to form, azo dye and condense with phthalic anhydride to produce fluorescence which show, intense green fluorescence when alkalized, , OH, , OH HO, , HO, , H, , H, , HO, , H2SO4, heat, , O, , OH, , O, , O, , O, O, O, , fluorescein, , Uses: Used as antiseptic in ointments , for the manufacture of dyes like azo dyes,, fluorescein, eosin etc, for preparing drugs used for curing hookworm and urinary, disorders etc., , Trihydric phenols:, Pyrogallol: obtained by heating gallic acid, OH, , OH, OH, +, , HOOC, , H2O, , 210 0, , OH, , C, , OH, , +, , H2CO3, , OH, , Properties: White crystalline solid, M.P. 1330C, soluble in water, alkaline solution turns, to brown, most powerful reducing agent., , Uses: Excellent photographer developer, for preparing ointments and antiseptic for skin,, as hair dyes, for absorbing oxygen in gas analysis, , Phloroglucinol: prepared by fusing resorcinol with NaOH in air, , UTTARAKHAND OPEN UNIVERSITY, , Page 66
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ORGANIC CHEMISTRY-II, OH, , BCHCH-202, OH, , +, , _1 O NaOH, 2 2, fuse, , OH, , HO, , OH, , Properties: White crystalline solid, M.P. 2180C, soluble in water alkaline solution, readly darken on exposure to air due to oxidation., , Uses: Used for detecting carbohydrates, producing a red coloration with in presence of, H2SO4., , 2.10 SUMMARY, In this unit we emphasis has been given to the introduction properties structure, physical, properties, chemical properties of phenols. This unit also describes the difference, between phenols and alcohols. Acidic character of phenols in comparison to alcohols and, carboxylic acids has been described. In chemical reactions both types of reactions, due to, –OH group and due to aromatic ring which are basically electrophilic in nature have, been described in detail. The important name reactions involving phenols havs been, described in this unit. Besides simple phenol, substituted phenols like cresols, pyrogallol,, catechol, thymol, carvacrol, resorcinol, flurogocinol etc have been described with their, properties and industrial application., , 2.11 TERMINAL QUESTION, Q.1 Tick the correct option (MCQs):, i. Structure of gallic acid is:, OH, , OH, , A., , B., HO, , COOH, , HO, , OH, , CH, , 3, , OH, OH, , C., , D., HO, , OH, , HOOC, , UTTARAKHAND OPEN UNIVERSITY, , OH, , Page 67
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ORGANIC CHEMISTRY-II, , BCHCH-202, , ii. Vanillin is obtained by using:, A. Reimer-Teiman Reaction, , B. Hoffman bromide Reaction, , C. Houben-Hosches Reaction, , D. Gatterman Reaction, , iii. Which is most acidic? :, OH, , OH, , A., , B., NO2, , OH, , OH, C., , D., , iv. Thymol, , Cl, , can be obtained naturally from:, , A. Thymus, , B. Acasia, , C. Rose, , D. None of them, , v. Commercially phenols can be obtained from:, A. Coal- tar, , B. Benzene, , C. Gasoline, , D. Wood, , vi. Phenol when treated with ZnO gives., A. Cyclohaxenol, , B. Benzene, , C. Cyclohexanone, , D. hydroquinone, , vii. Phenol undergoes ionization to become more stable by reacting with, A. negative ions, , B. positive ions, , B. both A and B, , D. neutral atoms, , UTTARAKHAND OPEN UNIVERSITY, , Page 68
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ORGANIC CHEMISTRY-II, , BCHCH-202, , viii. Condensation of phenol with HCHO to produce Bakelite is an example of:, A. Aldol condensation, C. Beckmann reaction, , B. Lederer-Manasse reaction, D. Knoevengal reaction, , ix. Which of the following groups will increase the acidity of phenol?, A.NO2, , B. CN, , C. halogens, , D. all, , x. Upon reflexing phenol with (CH3COO)2Hg we get., OH, , OH, O, , HgCOCH3, , A., , B., HgH, HgOH, , OH, Hg, , C., , OCOCH3, , D., , Q.2. Write the Mechanism of following name reactions, 1. Kolbe reaction, 2. Fries rearrangement, 3. Reimer Tiemann, 4. Reimer –Teiman reaction, Q.3. Arrange the following in order of increasing acidic strength. Giving reason:, p- Nitro phenol, m-Nitro phenol, o-Nitro phenol., Q.4. Explain why phenols do not undergo substitution of OH group like alcohol., Q.5 Explain why phenols are more acidic than alcohols., Q.6. How will you convert phenol to:-, , UTTARAKHAND OPEN UNIVERSITY, , Page 69
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 1. Salysilic acid, 2. Phenolphthalein, 3. Picric acid, 4. Ethoxy benzene, 5. Azo dye, 6. Catechol, , 2.12 ANSWERS (MCQs), 1-D, , 2- A, , 3- B, , 4- A, , 5- A, , 6- B, , 7- A, , 8- B, , 9- D, , 10- D, , 2.13 REFERENCES, 1., , Jerry march, Advanced Organic Chemistry, 4th edition, Wiley India, 2010., , 2., , P.S. Kalsi, Organic Reactions and their Mechanisms, New Age International, Private Limited; Publishing year: 2017., , 3., , Goutam Brahmachari, Organic name reactions, Narosa publishing house, New, Delhi (Revised version: 2012., , 4., , R.T.Morrison and R.N.Boyd Organic Chemistry, 6th edition, Prentice Hall Private, Limited, 1997., , 5., , Advanced Organic Chemistry by F.A.Carey and R.J.Sundberg, Plenum Pub. 5th, Edition, 2007, , 6., , S.M. Mukherji and S.P. Singh, Reaction Mechanism in Organic Chemistry, Trinity Press 2016., , 7., , B.S. Bahal, A. Bahal. Advanced organic chemistry. S. Chand & Company Ltd., Ram Nagar, New Delhi 1993, , UTTARAKHAND OPEN UNIVERSITY, , Page 70
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT -3 ETHERS AND EPOXIDES, CONTENTS:, 3.1 Objectives, 3.2 Introduction, 3.3 Nomencleature of ethers, 3.4 Methods of preparation, 3.5 Physical properties, 3.6 Chemical properties, 3.7 Summary, 3.8 Terminal questions, 3.9 Answers (MCQs), 3.10, , References, , 3.1 OBJECTIVES, The objectives of this unit are to make aware the students about ethers, to state the, IUPAC name of ethers, to name ethers either as alkoxyalkanes or as dialkyl ethers,to, name epoxides as oxiranes or as epoxyalkanes, to state the means to prepare ethers from, 1o alcohols, to draw the mechanism for the preparation of an ether from the reaction of, an alkene and an alcohol in the presence of an acid catalyst, to draw the mechanism for, the preparation of an ether from the reaction of a 1o alkyl halide and an unhindered, alkoxide,to draw the mechanism and discuss about the major product of the reaction of, an ether with excess HX, to draw the mechanism and give the major product of the, reaction of a vicinal halohydrin with hydroxide, including stereochemistry, to draw the, mechanism and give the major product of the reaction of an epoxide with a strong, nucleophile and to draw the mechanism and give the major product of the reaction of an, epoxide with either ROH/H+, HX, or H2O/H2SO4, , 3.2 INTRODUCTION, Ethers are compounds that containing single oxygen atom bonded to two alkyl groups,, two aryl groups or one aryl and one alkyl group. The general formula, of ethers is, CnH2n+2O. They are isomeric with the aliphatic monohydric alcohols with the general, , UTTARAKHAND OPEN UNIVERSITY, , Page 71
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ORGANIC CHEMISTRY-II, , BCHCH-202, , formula CnH2n+1OH. Thus, ethers can be represented as R -O –R', where R and R' may, be alkyl or aryl groups. When the two substituent groups (R and R'are identical, then, the ether is called a simple or symmetrical ether, otherwise if these two groups are, different, then the ether is known as a mixed or unsymmetrical ether. Diethyl ether,, C2H5OC2H5,, , is, , symmetrical, , ether, , whereas, , C2H5OCH3and, , C2H5OC6H5 are, , unsymmetrical ethers. The symmetrical diethyl ether is commonly also referred simply, as ether because of its wide use as a solvent for reactions and extraction of organic, compounds. It was also used as an anaesthetic for over hundred years. Ethers are, distinguished from other organic compounds because they lack a continuous chain of, carbons., , H, , .., O, .., , H, , R, , .., O, .., , R, , Ethers are thought of as alkyl analogues of water., Substitution of the hydroxyl hydrogens of alcohols by hydrocarbon groups gives, compounds known as ethers. These compounds may be classified further as open-chain,, cyclic, saturated, unsaturated, and aromatic, and so on.The oxygen atom of the ether can, also be part of a ring, in which case the ether is known as cyclic ether or also called, epoxide. Epoxides are formed when an oxygen atom is linked to carbon atoms of a, carbon chain forming a three membered ring. Epoxides are heterocyclic compounds, containing oxygen atom as a hetero atom. Epoxides have considerable ring strain., Epoxides are special kinds of ethers. These compounds are special because they have a, three member ring that contains an oxygen atom. They are far more reactive than, typical ethers. Tetrahydrofuran is one such cyclic ether which is used as a solvent., Ethers are commonly used as solvents for organic reactions., , UTTARAKHAND OPEN UNIVERSITY, , Page 72
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Cyclic ethers generally termed as epoxides in IUPAC system. Epoxide contains a 3membered ring between oxygen and two carbons ethers., , O, , O, H3C, , propylene oxide, , epxyethane, 1,2, , ethylene oxide, , epoxypropane, , 3.4 METHODS OF PREPARATION, There are different methods for the synthesis of ethers some of which are being, described as follow:, , 1. By Dehydration of alcohols: (a) The formation of reaction product, alkene or ether, depends on the reaction conditions. This method involves heating of excess of primary, alcohol with concentrated sulphuric acid and the temperature has to be maintained, around 4130 K to get symmetrical ether., , If alcohol is not used in excess or the, , temperature is higher, the alcohol will preferably undergo dehydration to yield alkene., ROH, , H 2SO 4, , R, , heat, , O, , H 2 SO 4, , CH 3 CH 2OH, , H 2 SO 4, 160 o, , +, , H 2O, , CH 3CH 2, , 140 oC, , CH 3 CH 2OH, , R, , CH 2, , O, , CH 2, , CH 2 CH 3, , +, , H 2O, , C, , Mechanism:, [i] CH 3 CH 2, , [ii], , .., OH, .., , CH 3 CH 2, , +, , .., OH, .., , H+, , +, , CH 3 CH 2, , CH 3CH 2, , +, O, .. H 2, , +, O, .. H 2, , CH 3 CH 2, , .., O + CH 2CH 3, , +, , H 2O, , H, [iii] CH 3CH 2, , .., O + CH 2 CH 3, , CH 3CH 2, , O, , CH 2 CH 3, , +, , H+, , H, , UTTARAKHAND OPEN UNIVERSITY, , Page 75
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ORGANIC CHEMISTRY, CHEMISTRY-II, , BCHCH, BCHCH-202, , c) Solubility: Ethers are slightly polar, and can hydrogen-bond, bond to water, although very, weakly, through the oxygen atom. Because ethers have no O, O-H, H bonds, they cannot, , participate in hydrogen bonding to the same extent that alcohols do. Nevertheless, the, oxygen in the ether can form a hydrog, hydrogen, en bond to the hydrogen in water. The presence, , of only single site on the ether for a limited kind of hydrogen bonding interaction means, that ethers generally have significantly smaller solubilities in water than do alcohols., Still they have higher solubil, solubilities, ities than any hydrocarbon. These are extremely volatile, and highly flammable (easily oxidized in air)., , Ethers containing upto three carbon atoms are soluble in water, due to their hydrogen, bond formation with water molecules., , The solubility decreases with increase in the number of carbon atoms. The relative, increase in the hydrocarbon portion of the molecule decreases the tendency of H, H-bond, formation. Ethers are appreciably soluble in organic solvents like al, alcohol,, cohol, benzene,, acetone etc., Water solubility order: alcohols > ethers > alkanes, , 3.6 CHEMICAL PROPERTIES:, Ethers have geometry similar to water and alcohols. The oxygen atom is sp3 hybridised., Since the carbon-oxygen, oxygen bond is polar and the molecule has a bent structure, there is a, , net dipole moment and the ether molecule is polar is nature. Ethers, thus, act as polar, solvents. Ethers are quite stable compounds. These are not easily attacked by alkalies;, dilute mineral acids, active metals, reducing agents or oxidising agents under ordinary, conditions., , 1. Reaction with acids: Being Lewis bases, ethers form complexes with Lewis acids, such as BF3, AlCl3, FeCl3, etc. These complexes are called etherates., , CH3CH2, :O :, CH2CH3, , CH3CH2, +, , BF3, , :O, , BF3, , CH2CH3, boron trifluoride etherate (complex), , UTTARAKHAND OPEN UNIVERSITY, , Page 80
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Similarly, diethyl ether reacts with Grignard reagent forming Grignard reagent etherate., CH2CH3, CH3CH2, :O :, , 2, , R, , CH3CH2, +, , O, , :O, , RMgX, , CH2CH3, , CH3CH2, , Mg, , CH2CH3, , X, , Grignard reagent eterate, Due to the formation of the etherate, Grignard reagents dissolve in ether. That is why, Grignard reagents are usually prepared in ethers. However, they cannot be prepared in, benzene, because benzene has no lone pair of electrons and therefore, cannot form, complexes with them., , 2. Action of hydroiodic acid: Following reactions takes place when ethers are treated, with haloacids., (a) With cold HI, C2H5OC2H5 + HI —————→ C2H5I + C2H5OH, Diethyl ether, , Ethyl iodide, , Ethyl alcohol, , (b) With hot HI, R – O – R' + 2HI ——————→ RI + R'I + H2O, , O, , CH 2 CH, , 3, , H, , I, , H, O, +, , CH 2 CH, , OH, , 3, , :I, , -, , phenol, CH 3 CH 2 -I, , Phenyl ethers are slightly different, and cleave to give alkyl halides and phenols. The, reaction stops at the phenol stage since the sp2 carbon of the C-O bond does not allow, the required SN1 or SN2 reactions to generate the second molecule of aryl halide., , 3. Reaction wtih HBr: Since the oxygen atom of ethers contains lone pairs of electrons,, they can accept a proton from the acids. Thus, ethers are basic in nature. Ethers are, stable to bases, but acidic conditions leads to the protonation of the ether oxygen, which, then can undergo substitution reactions., , UTTARAKHAND OPEN UNIVERSITY, , Page 81
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Al2O3, C2H5OC2H5 ———————→ 2CH = CH2 + H2O, 300o, , 8. Acid and base catalyzed ring opening: Unlike straight chain ethers, epoxides are very, reactive and are useful intermediates because of their chemical versatility. Epoxides, react to release their considerable strain energy. The acidic hydrolysis of epoxides gives, , H, O, , H, H O H, +, , H, , -H+, +, O H, , H, , H, , H, OH, H, OH, , H2O:, trans-cyclopentane-1,2-diol, , anti diols. Proton transfer from the acid catalyst generates the conjugate acid of the, epoxide, which is attacked by nucleophiles such as water. The result is antihydroxylation of the double bond. This hydration of an epoxide does not change the, oxidation state of any atoms or groups., Epoxides ring can also be opened by alcohols with acidic catalysis to generate alkoxy, alcohols with anti stereochemistry., , CH, , H, OH, H, OH, , 3 CO 3 H, , +, , H , H 2O, , The reaction of hydroxide (or alkoxide) with a symmetric epoxide generates anti diols, (or alkoxy alcohols) identical to those produced under acidic conditions., , H, O, H, HO:, , H, OH, OH, , H 2O, , H, OH, H, OH, , -, , 9. Orientation of ring opening: Unlike most ether, oxacyclopropanes react readily with, nucleophilic reagents. These reactions are no different from the nucleophilic, , UTTARAKHAND OPEN UNIVERSITY, , Page 83
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ORGANIC CHEMISTRY, CHEMISTRY-II, , BCHCH, BCHCH-202, , displacements, except that the leaving group, which is the oxygen of the oxide ring,, remains a part off the original molecule. The stereochemistry is consistent with an SN2, mechanism because inversion of configuration at the site of attack occurs. Thus, cyclopentene oxide yields products with the trans configuration:, , Acidic conditions, also can be used for the cleavage of oxacyclopropane rings. An oxonium ion is formed, first, which subsequently is attacked by the nucleophile in an SN2 displacement or forms, a carbocation in an SN1 reaction. Evidence for the SN2 mechanism, which produces, inversion, comes not, ot only from the stereochemistry but also from the fact that the rate is, , dependent on the concentration of the nucleophile. An example is ring opening with, hydrogen bromide:, , The same kind of mechanism can operate in the formation of 1,2-diols, 1,2 diols by acid-catalyzed, ac, ring-opening, opening with water as the nucleophile., , UTTARAKHAND OPEN UNIVERSITY, , Page 84
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ORGANIC CHEMISTRY-II, , H, , BCHCH-202, , H, , H Br, , H, OH, H, Br, , O+ H, , O, H, , H, , Br: -, , H-Br, Br, H, H, Br, , m ixture of, cis and trans, , Epoxides react with H-X to produce halohydrins, which react further with H-X to, generate 1, 2-dihalides., Unsymmetrical epoxides give products with different regiochemistry with basic, opening compared to acidic opening., CH3 OH, , CH3CH2OH, H+, , H3C, , H, H, , CH3CH2O, , O, , CH3 OCH2CH3, H, OH H, , H3 C, CH3, , H3C, , CH3CH2ONa, CH3CH2OH, , Under basic conditions, the alkoxide simply attacks the least sterically hindered epoxide, carbon in an SN2 displacement., , H, , 3, , C, CH, , H, , 3, , C, , O, , CH, 2, , 3, , CH, , 2, , CH, , OH, , 3, , OCH, , 3C, , 2, , CH, , 3, , H, O-, , H, , CH, , 3, , OH, , CH, H, , 3, , 3, , OCH, , C, , 2, , CH, , 3, , H, HO, , H, , Under acidic conditions, the alcohol seems to attack the more hindered carbon, but it is, more complicated. The protonated epoxide has several resonance structures., , UTTARAKHAND OPEN UNIVERSITY, , Page 85
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 3.7 SUMMARY, In this unit we learnet that. Ethers possess the structure: R − O − R’ and are compounds, having the general formula CnH2n+2O. Ethers are isomeric with the aliphatic monohydric, alcohols with the general formula CnH2n+1OH. We learnet that epoxides are the three, membered cyclic ethers.This unit also made us aware that the symmetrical or simple, ethers have R and R’ being identical while unsymmetrical or mixed ethers have, different R and R’ groups. We learnet that ethers are characterized by the C-O-C bond, and can be classified into linear and cyclic compounds. This unit described that in, comparision to alcohols, ethers are fairly unreactive except to very strong acids such as, HI or HBr. This low reactivity makes them useful as solvents, e.g. diethyl ether,, (C2H5)2O and tetrahydrofuran (THF), C4H8O. The more reactivity of epoxides over, simple ethers due to some ring strain and capability to react with nucleophiles resulting, in ring opening reaction has also been described in this unit. It has been described in, this unit that under acidic conditions, epoxides open by SN1 way with the nucleophile, attacking the more substituted end. The general modoe of synthesis of ethers and cyclic, ethers have been described in this unit besides their important reactions., , 3.8 TERMINAL QUESTIONS, Q.1 Tick the correct option (MCQs), i. IUPAC name of the following compound is, , CH3, , CH O CH3, CH3, , A. 1-methoxy-1-methylethane, , B. 2-methoxy-2-methylethane, , C. 2-methoxypropane, , D. isopropylmethyl ether, , ii. Ethers can exhibit isomerism, A. Metamesism, , B. Functional isomerism, , C. Both A and B, , D.Geometrical, , UTTARAKHAND OPEN UNIVERSITY, , Page 87
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (ii) Ethoxybenzene, (iii) 2-Methoxy-2-methylpropane, (iv) 1-Methoxyethane, Q.5. Discuss polarity of ethers and compare it with the polar characters of alcohols., Q.6. Why Grignard reagent is prepared in ether discuss with reaction and reason., Q.7. Write a note on: Williamson’s synthesis., Q.8. How is diethyl ether prepared in laboratory? How does it react wit (i) PCl5 (ii) O2, (iii) cold concentrated H2SO4 (iv) Con. HI, Q.9. Discuss different properties and uses of ether, Q.10. Give general methods of preparation and properties of epoxides., , 3.9 ANSWERS (MCQs), i-C, , ii- C, , iii-B, , iv –A, , v- B, , vi – A, , vii- B, , viii.- C, , ix.- D, , x.- B, , xi – B, , xii- C, , xiii –B, , xiv- C, , xv- D, , 3.10 REFERENCES, 1. Jerry March, Advanced Organic Chemistry, Fourth edition Wiley India edition. 4th,, 2010., 2. P.S. Kalsi, Organic reactions and their Mechanisms, New age international, Publishers, 2017., 3. S.M. Mukherji and S.P. Singh, Reaction Mechanism in Organic Chemistry Trinity, Press, 2017, 4. Goutam Brahmachari, Organic name Reactions, Narosa publishing house, New, Delhi, Revised version: 2012., 5. I.L. Finar, Organic Chemistry, Vol. II, 5th edition, ELBS & Longman group Ltd.,, 1974., 6. R.T.Morrision and R.N.Boyd, Organic Chemistry 6th edition, Prentice Hall Private, Ltd,. 1997., 7. Advanced Organic Chemistry, F.A. Carey and R.J. Sundberg, Plenum. 5th Edition,, 2007, 8. B.S Bahal, Arun Bahal, Advanced organic chemistry,1993, S Chand & Company Ltd., New Delhi., , UTTARAKHAND OPEN UNIVERSITY, , Page 90
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT 4: ALDEHYDES, CONTENTS:, 4.1 Objectives, 4.2 Introduction, 4.3 Structure and nomenclature of the carbonyl group, 4.4 Preparation of aldehydes, 4.5 Physical properties of aldehydes., 4.5.1 Relative reactivity of carbonyl compounds, 4.6 Chemical properties of aldehydes, 4.6.1 Addition reactions, 4.6.2 Addition reactions followed by elimination, 4.6.3 Reduction reactions of aldehydes, 4.6.4 Oxidation reactions of aldehydes, 4.6.5, , Other reactions:, , 4.7. Summary, 4.8. Self assessment, 4.8.1 Fill in the blanks, 4.8.3, , True/false, , 4.8.3 Short answer questions, 4.8.4 Questions related to important reactions:, , 4.1 OBJECTIVES, Objectives of this unit are to Study about:- Carbonyl Functional groups; molecular, orbital structure of functional group, reactivity of carbonyl group,n ucleophilicity vs., basicity, nucleophilicity of carbonyl group, types of reactions carbonyl group undergoes,, mechanism of name reactions, effect of conjugation on carbonyl group reactivity., , 4.2 INTRODUCTION, An aldehyde alkanals are an important class of an organic compounds containing a, functional group with the structure −CHO, consisting of a carbonyl center (a carbon, , UTTARAKHAND OPEN UNIVERSITY, , Page 91
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ORGANIC CHEMISTRY-II, , BCHCH-202, , double-bonded to oxygen) with the carbon atom also bonded to hydrogen and to an, alkyl/aryal group(s). The group—without alkyl/aryl moeity, also known as the formyl, group. Aldehydes are common in organic chemistry. Industrially aldehydes are produced, in lagre scale as starting material for synthesis of other important chemicals.viz HCHO is, produced more than 1.4 ,million tons/uear for the preparation ofresin .Traces of many, aldehydes are found in essential oils (terpenoids) and often contribute to their favorable, odors, e.g. cinnamaldehyde, cilantro, and vanillin. Possibly because of the high reactivity, of the formyl group, aldehydes are not common in several of the natural building blocks:, amino acids, nucleic acids, lipids. Most sugars, however, are derivatives of aldehydes., These aldoses exist as hemiacetals, a sort of masked form of the parent aldehyde. For, example, in aqueous solution only a tiny fraction of glucose exists as the aldehyde., , 4.3 STRUCTURE AND NOMENCLATURE OF THE, CARBONYL GROUP, R, Oxygen, , H, , p _ orbitals overlap, to form C _ O pi bond, loan pair in sp2 orbital, , R, sp2 carbon, trigonal planar, , C, , O, , H, , trigonal planar sp2 oxygen, loan pair in sp2orbital, , sigma _ bond between sp2 hybrid orbital of carbon and oxygen, , Carbonyl compounds have planar structure. It has a sp2 hybridized carbon atom and an, sp2 hybridized oxygen atom. The carbon uses two sp2 hybridized orbitals to form σbonds to the substituents. Two lone pairs of electrons are acomodated in sp2 hybridized, orbital of oxygen., , Nomenclature: - Common name for aldehydes are obtained from the names of the, corresponding carboxyllic acids., , UTTARAKHAND OPEN UNIVERSITY, , Page 92
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ORGANIC CHEMISTRY-II, , BCHCH-202, , O, , O, , H C OH, formic acid, O, , H C H, acetaldehyde, O, H3 C, , H3C C OH, acetic acid, , C H, , formaldehyde, O, , O, , CH3CH2 C OH, CH3CH2 C H, propionaldehyde, propionic acid, IUPAC names for aldehydes are obtained by replacing the ending –e of the, corresponding alkane with –al-. Aldehyde functional group is always terminal in chain., When other substituents are present, the carbonyl carbon is assigned number 1., , O, , O, , O, , H C H, , H3 C, , methanal, , CH3CH2, , C H, , ethanal, , C H, , propanal, O, C H, , Br, CH3, , O, , CH C H, , 2 _ bromopropanal, , benzaldehyde, , The electronegativity of carbon and oxygen is 2.5 and 3.5 respectively., Bond energy of C = O bond is 720 kjmol-1, Bond length of C = O bond is 1.21 A0., Carbonyl group C = O double bond is shorter then C – O single bond and stronger. C =, O bond is polarized and carbon atom has some degree of positive charge and this charge, attracts negatively charged nucleophiles and supports nucleophillic addition reaction., , NuNu, C, O, sp2, , C O, , electrophile, , C O ele., addition product, , Nucleophillic addition reactions of Aldehydes may be catalysed by acids or bases., , UTTARAKHAND OPEN UNIVERSITY, , Page 93
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ORGANIC CHEMISTRY-II, , BCHCH-202, , presence of HgSO4 as catalyst is converted into acetaldehyde., , 7. Alkaline hydrolysis of gem dihalides: - The germinal dihalides (two halogens atoms, are attached to the terminal carbon atom) gives Aldelyde, , OH, , Cl, H3C, , C, , H2O, , Cl, , NaOH, , H, , H3C, , C OH, , +, , 2 NaCl, , H, unstable, , O, H3C, , C, , H, , +, , H2O, , 8. Rosenmund’s Reduction: - This is one of the most common method for the synthesis, of aldehydes. In this method reduction of an acid chloride with hydrogen in boiling, xylene using a poisoned palladium catalyst supported on BaSO4 is used., , O, , [H], , R C Cl, , Pd/BaSO4, , O, CH3, , C Cl, , [H], Pd/BaSO4, , O, R C H, O, CH3, , C H, , Here BaSO4 prevents further reduction of aldehyde to alcohol as it acts as a poison to, Pd catalyst. So small amount of quinoline and sulphur is added to deactivate catalyst, partially. Lithium tri-t.butoxy aluminum hydride (LTBA) can also be used as catalyst., , 9. Oxo process: - It is an industrially important method to produce aldehydes. Here, alkene is treated with carbon monoxide (CO) and hydrogen in the presence of cobalt, carbonyl catalysts at high temperature and pressure., HCO(Co)4, R CH CH2 + H2, , heat, , UTTARAKHAND OPEN UNIVERSITY, , R CH CH2, , CHO, , H, , Page 97
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ORGANIC CHEMISTRY-II, 4.5, , BCHCH-202, , PHYSICAL PROPERTIES OF ALDEHYDES, , 1. In aldehyde the first member HCHO is gaseous at room temperature. Acetaldehyde is, liquid in nature with b.p. 200C. Lower aldehydes are colourless liquids.Benzaldehyde, is liquid with characteristic smell of bitter almonds., 2. Lower members of aldehydes possess unpleasant smell., 3. Carbonyl group compounds are polar in nature due to dipole - dipole interactions of, partial negative charge of carbonyl oxygen of one molecule and partial positive, charge on the carbonyl carbon of another molecule. So boiling points of aldehydes, and ketones are higher than those of alkanes which have comparable molecular, weights. However these dipole -dipole interactions are weaker than hydrogen, bonding interactions, hence aldehydes and ketones due to lack of intermolecular, hydrogen bonding have low boiling points as compared to alcohols of comparable, molecular weights., , O, , Mol. wt., b.p., , CH3CH3, , H C H, , ethane, , methanal, formaldehyde, 30, , 30, - 89, , 0, , C, , - 210, , C, , CH3OH, methanol, 32, 64.5, , 0, , C, , 4. As aldehydes and ketones can form hydrogen bonds with water so lower, aldehydes and ketones are soluble in water., , However solubility decreases as the hydrocarbon part of molecule increases. The lower, aldehydes and ketones are soluble in organic solvents such as benzene, ether and CCl4., Carbonyl compound also form hydrates with water i.e. corresponding germinal diols., , UTTARAKHAND OPEN UNIVERSITY, , Page 103
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 4.5.1 RELATIVE REACTIVITY OF CARBONYL COMPOUNDS, The carbony group of aldehydes is reactive because of electromeric effect. However the, electron withdrawing substituents make carbonyl group more electrophilic, as, withdrawing groups generates extra positive charge at carbonyl carbon and electron, donating alkyl groups reduce positive charge at carbonyl carbon. Increased positive, charge at carbonyl carbon destabilize carbonyl compounds and favours attack of, nucleophile at electron deficient carbonyl carbon which is followed by the addition of, electrophile on negatively charged oxygen., , R, , O, Cl2C, , O, , O, , H, , H, H, H3C, Nucleophile attacks C = O bond prior to, , O, , O, H, , R, , H, , electrophile because the produced anion is more stable than the cation resulting due to, electrophile attack., The reactivity of nucleophillic addition is favoured by, i. Electron withdrawing substituent at carbonyl carbon., ii. Small size of substituent group to avoid sterive hinderance for attacking reagent., During nucleophilic addition reaction carbonyl carbon transforms from SP2 hybrid state, to sp3 hybridized state and bond angle reduces from 1200 approx. to 109.50 approx. So, transition stage bears steric strain and this steric strain increases with increasing bulk of, groups which are already present on carbonyl carbon., Aromatic carbonyl compounds are less reactive than the corresponding aliphatic, carbonyl compounds. Here partial positive charge present on carbonyl carbon is, delocalized over benzene ring by resonance., , UTTARAKHAND OPEN UNIVERSITY, , Page 104
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ORGANIC CHEMISTRY-II, , BCHCH-202, , So electrophillic nature of carbonyl carbon which is desired for nucleophillic addition, reaction is neutralized and nuclecophillic addition reaction slows down. The acids and, bases act as catalyst for a number of carbonyl addition reactions. Here acids catalysts, make carbonyl group more electrophillic by protonating carbonyl groups lone pair and, base catalysts make nucleophile more nucleophillic by deprotonating nucleophile., , 4.5, , CHEMICAL PROPERTIES OF ALDEHYDES, , The slightly positive carbon atom in the carbonyl group can be attacked by, nucleophiles. A nucleophile is a negatively charged ion (for example, a cyanide ion,, CN-), or a slightly negatively charged part of a molecule. Some of the important, reactions of adlehydes are being given below, , 4.6.1 ADDITION REACTIONS, During the reaction, the carbon-oxygen double bond gets broken. The net effect of all, this is that the carbonyl group undergoes addition reactions., (1), , Addition of Sodium Bisulphite – Aldehydes add on sodium hydrogen sulphite to, form bisulphite compounds., , R, , R, C = +Na HSO3, H, , H, , R, , OH, C, , or, SO3Na, , OH, C, , H, , Na, SO3, , Thus the formed bisuphite compounds are hydroxysulphonic acid salts where sulphur, atom is directly attached to the carbon atom. When bisulphate compounds are heated, with dilute acid or Na2CO3 solution then carbonyl compound is regenerated., , (2) Addition of hydrogen cyanide(HCN) - All Aldehydes add HCN in the presence of, base catalyst to form cyanohydrins., , UTTARAKHAND OPEN UNIVERSITY, , Page 105
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Hemiacetals are unstable. Here acid or base catalyse not only formation of hemiacetals, but also decomposition them into aldehyde., , When catalytic acid is added to acetaldelyde-methanol mixture rate of reaction, increases and two equivalents of alcohols are added to aldehyde to form new class of, compound called acetal., , UTTARAKHAND OPEN UNIVERSITY, , Page 108
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (7) Addition of mercaptans: Aldehydes condense with thioalcohols (mercaptans) in, the presence of HCl to form mercaptals., , 4.6.2 ADDITION REACTIONS FOLLOWED BY ELIMINATION, The addition reactions of aldehydes often followed by the loss of a water molecule. This, gives a reaction known as addition-elimination or condensation.The important reactions, in continuation to addition reactions as above (4.6.1) given by aldehydes are:, (8) Addition of ammonia Derivaties – Aldehydes combines with various compounds, of type Y — NH2 (Y = NH2, OH, C6H5NH etc) to form carbon nitrogen double, bonded compounds and a water molecule is eliminated., , (a) Hydroxylamine (NH2OH) form oximes with carbonyl compounds, , UTTARAKHAND OPEN UNIVERSITY, , Page 109
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (13) Reduction to hydrocarbon: Carbonyl group of compound is reduced to, methylene group by using zinc amalgam and hydrochloric acid.This reaction is called, , Clemmensen reduction.In this reaction carbonyl group is reduced to –CH2- group., Ketones are more effective than aldehydes in this reduction. The mercury alloyed with, the Zn does not participate in the reaction; it serves only to provide aclean active metal, surface. Some times alcohols may be used as the solvent in Clemmensen reduction, , UTTARAKHAND OPEN UNIVERSITY, , Page 114
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ORGANIC CHEMISTRY-II, , BCHCH-202, , H, R, , C, , H, , H, , R, , Zn Cl, , C, , H, , Cl, , – Zn Cl2, , R, , C, , H, , H, , Zn Cl Cl, , H, H, R, , C, , H, , H, , R, , Zn/Hg, con.HCl, , O, H, , CH3CHO, , Zn/Hg, con.HCl, , R, , H, C, , H, , H, , CH3CH2OH, , (14) Wolff-Kishner reduction: Hydrazones are hearted with Sodium ethoxide at 1800C,, Nitrogen is eliminated and carbonyl group is converted to methylene group i.e., hydrocarbon., O, R, , C, , OH, H + NH2 NH 2, , NaOH, , R, , C, , NH – NH2, , H, , UTTARAKHAND OPEN UNIVERSITY, , Page 115
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Benzaldehyde gives positive test with Tollen’s reagent but not with Fehling’s and, Benedict’s solution because of + Resonance effect of Benzene ring which makes C-H, bond stronger and weak oxidizing agents like Fehling and Benedict solutions could not, oxidize aromatic aldehydes., , 4.6.5 OTHER REACTIONS, The carbonyl groups are polar and this polarity increases acidity of hydrogens of αcarbon. These α- hydrogens may lead to form etholate ions. There enolatic ions are, good nucleophile and can attack on electrophiles like protons. The pKa value of, aldehyde is lower than that of ethane or acetylene but it is comparable to those of, alcohols. So α halogens of aldehydes are removable by strong bases., , alpha hydrogen, , H O, H C C H, , O, , O, , C C H, , C C H, , B, , +, , H, alpha carbon, Enolate ion is ambident anion. Here partial negative charge is located on both α carbon, and oxygen i.e. two different sites of one molecule are having –ve charges. So this, nucleophile can attack eleclrophiles at either of two sites., If electrophile like alkyl group attacks at carbon then it is called alkylation or C-, , alkylation, or if it attacks at oxygen it is O-alkylation, O alkylation is uncommon and, oxygen site is common for protonation. Protonation leads to unsaturated alcohol called, alkenol or enol which are unstable and rapidly isomerizes back to carbonyl, compound.Some of the reactions under this had in continuation are being given follow:, , UTTARAKHAND OPEN UNIVERSITY, , Page 117, , BH
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Mechanism : Attack of OH(–) group on the carbonyl group followed by hydride, transfer.The sequential mechanism is as follow both forinter and intramolecular, Cannizzaro reaction, Na+, , NaOH, , +, , OH, O, , O, H C, , H, , +, , H C, , OH, , O, , O, H, , +, , H C, , H, , hydride shift, , H C H, , OH, , H, +, , O, , O, +, , H C ONa, , Na, , +, , H C O, , O, +, , O, , H C H, , CH3OH, , +, , H C OH, , H, OH, H C O, +, , OH, , NaOH, , H C O, H C O, , H C O, , O H, C, , O, , H C, , O, , hydride shift, intramolecular, , glyxol ( ethanedial), , H, , ONa, , OH, C O, H C OH, H, hydroxy acetic acid, , H3 + O, , O, , C O, , C O, +, , Na, H C OH, , +, , H C OH, , H, , H, , In mixed Cannizzaro reaction it is the formaldehyde that is oxidized to formate ion and, other aldehyde viz; benzaldehyde is reduced to alcohol because CHO group of HCHO, is the most electrophilic among all the substituted aldehydes and require the least, activation energy to react with nucleophile reagent like -OH ion., , 18. Reformatsky reaction: Carbonyl compounds on treatment with α- bromoester in, the presence of zinc, followed by acid hydrolysis yields β hydroxyl ester., , UTTARAKHAND OPEN UNIVERSITY, , Page 119
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ORGANIC CHEMISTRY-II, , BCHCH-202, O, R CH =CH C O CH 2 CH 3, alpha, beta unsaturated ester, , OH, , O, , R CH CH 2, , C, , CH 3 O H /H O H /H +, , OCH 2 CH 3, , O, R, , CH, , CH =C, , O CH 2 CH 3, , Examples of Reformatsky reaction:, OH, CH 3 CH 2 CH O, , +, , BrCH 2 CO O CH 2 C H 3, , CH 3 O, CH 3 CH O, , Br, , +, , C, , C, , O CH 2 CH 3, , i Zn/C/H 6 /heat, CH 3 CH 2 CH CH 2 CO O CH 2 CH 3, , ii N H 4 Cl/H O H, , O H CH 3O, , i Zn/ether/heat, , CH 3 CH C, , ii N H 4 Cl/H O H, , CH 3, , C, , O CH 2 CH 3, , CH 3, OH, , O, CH, , C, , OCH 2CH 3, , CH 3, , O, , CH 3 O, +, , H, , Br, , CH, , C, , OCH 2CH 3, , i Zn/C/H 6 /heat, ii HOH/H +, O, C, , C, , OCH 2 CH 3, , CH 3, , O, CH 3, , C, , N, , +, , Br, , CH 2, , C, , OCH 2 CH 3, , O, , O, , i Zn/C/H 6/heat, , CH 3, , ii HOH/H +, , C, , CH 2, , C, , OH, CH 3, , CH 2, , CH, , OCH 2 CH 3, , O, CH 2, , CH 3, , C, , N, CH 3, , O, CH 3CH 2CHO, , +, , Br, , CH 2, , C, , N, , CH 3, , i Zn/ether/C 6 H 6/heat, , CH 3, , ii HOH/NH 4 Cl, , HOH/OH/heat, O, CH 3, , CH 2, , CH, , CH, , C, , CH 3, N, CH 3, , UTTARAKHAND OPEN UNIVERSITY, , Page 121
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ORGANIC CHEMISTRY-II, , BCHCH-202, , OH, , OH, +, , HCHO, , H+, , N H, , +, , CH2, , N, , R, N, CH2, , OH, +, , HCHO, , +, , R, OH, , H+, , R2NH, , R, CH2, +, , HCHO, , +, , N, , N, , R, , H+, , R2NH, , N, , H, , H, 22. Knoevenagel reaction:It is a modified aldol condensation. In is simply a, nucleophilic addition of active hydrogen to the carbonyl group which finally undero, dehydration with the formation of α, β- unsaturated product.This reaction is catalysed, by amines generally piperidine/buffer system containing an amine and acid. A base is, required to generate carbanion while acid is for activation carbonyl group., Active hudrogens, H, O, R, , i, R, , ii, , X, , H, C, , X, , X, , R, , R, , X, , Base, , X = electron withdrawing group, XCH2X may be, O, , O, , O, diethyl malonate, , O, O, , O, , O, :, O, , ethyl acetoacetate (EAA), , UTTARAKHAND OPEN UNIVERSITY, , O, , HO, malonic acid, , O, OH, , N, , C, , OH etc;, cynoacetic acid, , Page 127
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ORGANIC CHEMISTRY-II, 4.7, , BCHCH-202, , SUMMARY, , Aldehydes are compounds having general formula CnH2nO and contain Oxo (Carbonyl), group >C=O. Here functional group –CHO occurs at the end of a chain. Primary, alcohols are oxidized to aldehydes only by Collins reagent (CrO3.2C5H5N) and Corey’s, reagent (CrO3.C5H5N, PCC). Aldehydes undergo nucleophillic addition reactions due to, polarity of carbonyl group. Reactivity of aldehydes towards nucleophillic addition, reactions decreases as steric hindrance and +I effect of attached alkyl group increases., Aldehydes are easily oxidized, so they work as powerful reducing agents (reduce, Fehling solution and Tollen’s reagent). Aldehydes give a series of condensation, reactions and alpha hydrogen substitution reactions as per their structural, constitution.Aldehydes can be used as starting materials for the synthesis of other, synthetically important compounds., , 4.8 SELF ASSESSMENT, , 4.8.1 FILL IN THE BLANKS :, (1) The carbon of carbonyl carbon is ___________ hybridised., (a) sp3, , (b) sp2, , (c) sp, , (d) sp3d, , Ans. :- (b), (2), , Boiling points of primary alcohols are __________ than the boiling points of, corresponding aldehydes., (a) higher, , (b) lower, , Ans :- (a), (3), , Aldehydes are prepared by the oxidation of _____________, (a) Primary alcohol (b) Secondary alcohol, , (c) Tertiary alcohol, , Ans :- (a), , UTTARAKHAND OPEN UNIVERSITY, , Page 132
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ORGANIC CHEMISTRY-II, (4), , BCHCH-202, , Melting points of aldehydes tend to __________ with increasing molecular weight., (a) decrease, , (b) increase, , (c) remain unchanged, , Ans :- (b), (5), , Aldehydes have ________ boiling points compared with those of alcohols., (a) low, , (b) high, , Ans. :- (a) low, (6), , Catalytic hydrogenation readily converts aldehydes to __________ alcohols., (a) Primary, , (b) Secondary, , (c) Tertiary, , Ans. :- (a), (7), , Aldehydes having α-hydrogen atoms usually do not undergo ________ reaction, under its reaction condition., (a) Cannizaro, , (b) Aldol, , (c) Haloform, , Ans. :- (a), (8), , Appearance of silver mirror in Tollen’s test indicates the presence of, (a) Alcohol, , (b) Aldehyde (c) Alkene, , (d) alkane, , Ans. :- (b), (9), , Acetaldehyde on treatment with Fehling solution gives a precipitate of (a) Cu, , (b) Cu2O, , (c) CuO, , (d) CuCl2, , Ans : - (b), (10) Acetaldehyde on boiling with chlorine gas gives –, (a) CH3, , C, O, , Cl, , (b) C Cl3, , C, , H, , (c) CH3 CH Cl2, , (d) CHCl3, , O, , Ans. :- (b), , UTTARAKHAND OPEN UNIVERSITY, , Page 133
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 4.8.2 TRUE/FALSE, 1., , Both carbon and oxygen of ………group is sp2 hybridised., , 2., , IUPAC names of aldehydes are obtained by replacing the ending –e of the, corresponding alkane with –al., , 3., , Controlled oxidation of secondary alcohols using an acidified solution of K2Cr2O7, produces aldehydes., , 4., , Hydration of acetylene yields acetaldehyde., , 5., , Density of aldehydes is less than water., , 6., , Lower aldehydes are insoluble in water., , 7., , As hydrocarbon part of aldehyde “compound increases solubility also increases., , 8., , Carbon atom next to carbonyl group is called α-carbon., , 9., , Wolf kishner reduction of aldehydes involves use of basic solution of Hydrazine as, reducing agent., , 10. Aldehydes react with PCl5 to form gem – dihalides., , Ans. :- 1. T, 2. T, 3. F, 4. T, 5. T, 6. F, 7. F, 8. T, 9. T, 10. T, , 4.8.3 SHORT ANSWER QUESTIONS, 1. Writing the structures arrange the following compounds in increasing order of their, reactivity in nucleophillic addition reaction., (a) Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Ans :- p tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde, 2. What is the structure of carbonyl group? How does it react with (i) HCN (ii) NaHSO3, 3. What happens when formaldehyde is treated with NaOH ?, 4. Explain the reaction mechanism when acetaldehyde is treated with NaOH ?, , UTTARAKHAND OPEN UNIVERSITY, , Page 134
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 3. F.A. Carey and R.J. Sundberg, Advanced Organic Chemistry, Plenum. 5th edition,, 2007, 4. Jagdamba Singh and L.D.S.Yadav, Organic Chemistry vol. I, 8th edition-2013 Pragati, Prakashan Pub., 5. S.M. Mukherji and S.P. Singh, Reaction Mechanism in Organic Chemistry, Trinity, Press, 2016., 6. B.S. Bahal, A. Bahal. Advanced Organic Chemistry. S. Chand & Company Ltd. Ram, Nagar, New Delhi 1993., , UTTARAKHAND OPEN UNIVERSITY, , Page 137
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT -5 KETONS, CONTENTS:, 5.1 Objectives, 5.2 Introduction, [, , 5.3 Nomenclature, 5.4 Synthesis of ketones, 5.5 Preparative methods of aromatic ketones, 5.6 Physical properties, 5.7 Chemical properties, 5.7.1 Addition reactions, 5.7.2 Addition reactions followed by elimination, 5.7.3 Reduction reaction, 5.7.4 Oxidation reaction, 5.7.5 Other reactions, 5.7.6 Some reactions of aromatic ketones, 5.8 Summary, 5.9 Terminal Question, 5.10 References, , 5.1 OJECTIVES, The objectives of this unit are to study about functional group carbony, Molecular, orbital structure of functional group, reactivity of carbonyl group, nucleophilicity of, carbonyl group.To study types of reactions carbonyl group undergo, mechanism of, name reactions, effect of conjugation on carbonyl group reactivity.Although we already, have discussed above factors in aldehydes unit. Now we will discuss the changes, because of replacement of group H by an alkyl group., , UTTARAKHAND OPEN UNIVERSITY, , Page 138
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 5.2 INTRODUCTION:, In chemistry, a ketones (alkanone) are an organic compound with the structure RC (=O), R’, where R and R' can be a variety of carbon-containing substituents. Structurally the, ketone carbon is often described as "sp2 hybridized", a description that includes both, their electronic and molecular structure. Ketones are trigonal planar around the ketonic, carbon, with C−C−O and C−C−C bond angles of approximately 120°, , sp3 hybrid R group, 2, , R, , R, , sp carbonyl carbon, , O, , C O, , sp, , 2, , oxygen, , R', R, sp3 hybrid R group, Basic skeletal structure of carbonyl group in ketone is same (Planer) as in aldehydes., , 5.3 NOMENCLATURE, Common names of ketones are named on the basis of the alkyl group attached to the, carbonyl group. In IUPAC nomenclature ketones are designated by suffix – one. Prefix, is the name of hydrocarbon (Alkanones). Here longest hydrocarbon chain containing, carbonyl carbon is selected and named it by substituting ‘e’ of Alkane with ‘one’. While, numbering the chain lowest number is given to carbonyl carbon. Other substituents are, numbered named and placed as prefixes in alphabetic order. If there are two carbonyl, groups in a molecule, it is named as Alkanedione., , UTTARAKHAND OPEN UNIVERSITY, , Page 139
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Here exchange reaction takes place, , Step-II, R1, Al, , O, CH3, , C, , H, , CH3, R2, , R2, H, , C, O, , C, , O, , R1, , CH3 + Al, , O, , C, , 3, , CH3, , 3, , New complex is formed., , Step-III, , Similarly two more moles of acetone will react with above (one mole) formed complex, and give two more moles of ketone product., O, R2, 3 CH3, , C, , CH3 + Al, , O, , C, R1, H, , 3 R1, 3, , UTTARAKHAND OPEN UNIVERSITY, , C, O, , R2 + 3, , CH3, , H, C, , H3C, , O, , Al, 3, , Page 142
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ORGANIC CHEMISTRY-II, , BCHCH-202, , This reaction is useful as for oxidation of polyfunctional compounds as this reaction, conditions are mild. For e.g. in unsaturated alcohols as it (reagent) does not affect, double bond., Primary alcohols can also be oxidized by [(CH3) 3 CO] 3 Al if in acetone is replaced by, p benzoquinone as it is better hydrogen acceptor than acetone., , 3. By heating calcium salt of any monocarboxylic acid other than formic acid, ketones, are obtained., , 4. When vapours of any monocarboxylic acid except formic acid are passed over, Manganous oxide at 3000C then ketone is obtained., , Mixture of monocarboxylic acids yield mixed ketones, , Besides this R′COR′ and R2 COR2 are also obtained., , 5. From Alkenes: Ketones can be prepared from alkenes as follow., (a) Ozonolysis: - Alkenes of following types when treated with ozone, yield ozonides, and this on subsequent treatment with H2O and zinc dust yield ketones, , UTTARAKHAND OPEN UNIVERSITY, , Page 143
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (10) Organo Cadmium compounds on reaction with acid chloride form ketones., O, R2 Cd + 2R1 COCl, , 2R, , C, , R1 + Cd Cl2, , Reaction of cadmium chloride with Grignard reagent gives Organo Cadmium, compounds., 2 R – Mg – X + Cd Cl2, , R2 Cd + 2 Mg X Cl, , Here R is primary alkyl group or aryl group., , 5.6 PHYSIICAL PROPERTIES, 1. Lower ketones are colourless liquids., 2. Lower ketones possess pleasant, sweet odours., 3.Density of ketones is less than water., 4. As discussed in aldehyde unit ketones have higher boiling points than corresponding, alkanes but lower boiling points compared with those of alcohols of comparable, molecular weights., CH3, CH3 — CH — CH3, , mol. wt., , O, , OH, , CH3 — C — CH3, , CH3 — CH — CH3, , 58, , boiling Point–120C, isobutane, , 58, , 60, , 560C, , 82.50C, , acetone, , isopropyl alcohol, , 5. Lower ketones are soluble in water as they form hydrogen bonding with water. As, alkyl chain of molecule increases, solubility in water decreases.., R, , δ–, , C, R, , δ+, , δ+, , O ..... H, O, , R, , δ–, , H ...... O, , C, R, , In infrared spectrum strong C = O Stretching band is observed in 1700 – 1740 cm–1, region., , UTTARAKHAND OPEN UNIVERSITY, , Page 149
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Relative Reactivity: As discussed in detail in aldehyde unit it is to be noted that, relative reactivity of ketones is less than aldehydes towards nucleophillic addition, reaction. Here electron releasing alkyl group reduce positive charge of carbonyl carbon, and thereby decrease reactivity of carbonyl group. Moreover as compare to H atom, alkyl group increases steric hindrance for attacking reagent (nucleophile) to reach at, carbonyl carbon. Secondly after attack sp2 hybridised carbonyl carbon becomes sp3, hybridised in resultant adduct. Here bond angles are reduced from appr.120° to around, 109º. This adducts also gets steric strain due to increase of bulky groups. This strain is, higher in ketones as compared to aldehydes., O, , O, CH3, , O, H, , CH3, , O, H, , H, NO2, , Acetophenone is ketone while other three are aldehyde. So, acetophenone is least, reactive. p-toulaldehyde has electron donating methyl group at para position of benzene, ring whereas p-nitrobenzaldehyde has an electron withdrawing nitro group at the para, position and we know that reactivity of carbonyl group is inversely proportional to, electron density at carbonyl carbon so p-toulaldehyde is less reactive than benzaldehyde, while p-nitrobenzaldehyde is more reactive than benzaldehyde.α-hydrogen of ketones, are acidic and removable by strong bases., , 5.7 CHEMICAL PROPERTIES, Ketones are reactive organic compounds and undergo many reactions like aldehydes., , 5.7.1 ADDITION REACTIONS:, Like aldehydes the reactive carbony group of ketones gives addition reactions., , (1) Addition of sodium bisulphate (NaHSO3) :- Ketones add on sodium hydrogen, sulphite and form adducts called bisulphite addition compounds which are water soluble, salts., , UTTARAKHAND OPEN UNIVERSITY, , Page 150
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ORGANIC CHEMISTRY-II, R, R, , BCHCH-202, , R, C= O + Na HSO3, , R, , OH, , C, , SO3 Na, , R, , OH, , or, , C, , SO3, , R, , Na, , Thus formed adduct when treated with acid, base gives corresponding carbonyl, compound., OH, , O, HCl / H2O, , R—C—R, , R — C — R + Na Cl + H2O + SO2, , SO3 Na, O, Na2CO3 / H2O, , R — C — R + Na2SO3 + NaHCO3, , Mechanism: - In this reaction Na2SO3 acts as nucleophile through sulphur and attacks, at carbonyl carbon which is followed by protonation of carbonyl anionic oxygen by, bisulphite ion., Na HSO3, , Na, , + H–O–S–O, O, , HOH + H – O – S – O, , H3 O + O – S – O, , O, , O, , O, , O, , O, , R — C — R', R—C—S—O, O—S—O, , R', , O, , O, , O, , O, , R—C—S—O, R', , OH O, + HSO3, , O, , UTTARAKHAND OPEN UNIVERSITY, , R—C—S—O, R', , + SO3, , O, , Page 151
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 5.7.5 OTHER REACTIONS:, Earlier it has been discussed the acidity of α- hydrogens in carbonyl compounds which, leads to different types of reactions in ketones eg. halogenation, condensation etc.In, continuity some of the reactions of ketones are being discussed as follow, , (16) Haloform Reaction: - Methyl ketones react rapidly with halogens (Cl2, Br2, I2) in, the presence of alkali to form mono, di and tri haloderivatives., , R, O, , +, , X2, , OH, , O, R C OH, , +, , R, ketone, , CHX3, haloform, , O, , CH3, O, , +, , H, , O, , I2, , OH, , H3C, , C OH, , CH3, , CHI3, iodoform, +, , Mechanism, , OH +, , H—C—C—R, H, , O, , O, , CH2 — C — R, X–X, , CH2 = C — R +, H2O, , X — CH2 — C — R, O, , It involves abstraction of hydrogen by alkali and then resonance stabilization of, conjugate base.Then carbanion displaces a halide from a halogen molecule.Introduction, of halogen to methyl ketone enhances electronegativity of remaining α- hydrogens and, they again undergo above process repeatedly forming trichalogenated ketones., , UTTARAKHAND OPEN UNIVERSITY, , Page 164
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ORGANIC CHEMISTRY-II, X, , BCHCH-202, X, , O, , OH + H — C — C — R, , X O, , O, , H—C—C—R, , H — C = C — R + H2O, X—X, , H, X, , O, , H—C—C—R, X, , X, OH, , +, , O, , X, , O, , H—C—C—R, , X—C—C—R, , X, , X–X, , O, , X—C—C—R, , X, , X, , The trihalogenated ketones are unstable to base., X, , O, , X—C—C—R, , X, +, , OH, , X, , O, R—C—O +, , O, , X—C—C—R, OH, , X, , X, , X, , X—C—H, , O, , X—C, , X, , +, , X, , C—R, OH, , (17) Reformatsky Reaction: - Like aldehydes ketones also react with, , bromoester in, , the presence of Zinc which subsequently on acid hydrolysis result in, , -hydroxy, , ester., O, , OH, 1.Zn, Ether, , CH3 — C — CH3 + Br CH2 COO C2H5, , 2. H2O/H+, , CH3 — C — CH2 — C — OC2H5, CH3, , Acetone, , O, , Ethyl 3-hydroxy-3-methyl butanoate, , β- hydroxyl ester dehydrate to give unsaturated ester., , UTTARAKHAND OPEN UNIVERSITY, , Page 165
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ORGANIC CHEMISTRY-II, O, , O, , CHO, , CHO, Br, , Br, , ,, , ,, , BCHCH-202, , ,, , Ans – hydration increases with increasing H-bonding., O, , O, , CHO, , Br, , CHO, Br, , 3., O, Pt, 1 eq H2, Raney Ni, H2, , NaBH4, CH3 OH, , (A), (B), (C), , Identify (A), (B) and (C), Ans –, O, (A) is, , OH, (B) is, , OH, (C) is, , 4., , Compound A, having the empirical formula C7H8 is chlorinated in sunlight to give, , a product which is hydrolysed to produce B. B after oxidation reacts with acetic, anhydride in the Perkin reaction to produce an acid C which has an equivalent weight of, 148. Give the name and structure of A, B and C., Ans –, , UTTARAKHAND OPEN UNIVERSITY, , Page 178
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ORGANIC CHEMISTRY-II, CH3, , BCHCH-202, , CH2Cl, Cl2, H2, , Toluene, , CH2OH, H2O / OH, , Benzyl chloride, , [O], , Benzyl alcohol, , CH = CHCOOH, , CHO, Perkin, reaction, Benzaldehyde, , Cinnamic acid, , 5.10 REFERENCES, 1. I.L Finar Organic Chemistry. Vol. 2., 5th edition, ELBS & Longman group Ltd.,, 1974., 2. R.T.Morrison and R.N.Boyd Organic Chemistry, 6th edition, Prentice Hall Private, Ltd, 1997., 3. Organic Chemistry by Clayden,Greeves,Warren and Wothers 2nd edition 2012,, Oxford University Press, 4., , Jagdamba Singh and L.D.S.Yadav, Organic Chemistry vol. I, 8th edition-2013, Pragati Prakashan Pub., , 5., , F.A.Carey and R.J.Sundberg, Advanced Organic Chemistry, Plenum Pub. 5th, Edition, 2007, , 6., , S.M. Mukherji and S.P. Singh, Reaction Mechanism in Organic Chemistry Trinity, Press, 2016., , 7. B.S. Bahal, A. Bahal. Advanced Organic Chemistry. S. Chand & Company Ltd., Ram Nagar, New Delhi 1993, , UTTARAKHAND OPEN UNIVERSITY, , Page 179
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT -6 CARBOXYLIC ACIDS, CONTENTS:, 6.1, , Objectives, , 6.2, , Introduction, , 6.3, , Nomenclature of carboxylic acids, , 6.4, , Structure and bonding, , 6.5, , Physical properties, , 6.6, , Acidity of carboxylic acids and effect of substituents on acid strength, , 6.7, , Preparation of carboxylic acids, , 6.8, , Reactions of carboxylic acids, , 6.9, , Mechanism of decarboxylation, , 6.10 Methods of formation and chemical reactions of halo-acids, 6.10.1 Preparation of halo acids, 6.10.2 Chemical reactions of halo-acids, 6.11 Hydroxy acids: malic, tartaric and citric acids, 6.11.1 Physical properties of hydroxyl acids, 6.11.2 Preparation and chemical properties of hydroxy acids, 6.12 Summary, 6.13 Terminal Question, 6.14 Answers(MCQ), 6.15, , References, , 6.1 OBJECTIVES, The aim of this unit is to make you aware about carboxylic acids their common names, and IUPAC naming system. To explain the structure of carboxylic acids, describe the, acid strength of carboxylic acids, describe boiling points and solubility of carboxylic, acids in water,synthesis of, , carboxylic acids,d escribe the physical and chemical, , properties of carboxylic acids To discuss the methods for the conversion of carboxylic, acids into acid chlorides, esters and amides.To study the reduction of carboxylic acid, and understand about the mechanism of decarboxylation.To study how halo acids are, , UTTARAKHAND OPEN UNIVERSITY, , Page 180
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ORGANIC CHEMISTRY-II, , BCHCH-202, , synthesized from carboxylic acids? To describe the preparation, properties and uses of, hydroxyl acids: malic, tartaric and citric acids., , 6.2 INTRODUCTION, Carboxylic acids are aliphatic or aromatic compounds which contain at least one, carboxyl group (-COOH) in the molecule. The word “carboxyl” is derived from the, names of two functional groups i.e. carbonyl and hydroxyl. Carboxylic acids are, classified as mono, di, tri, or polycarboxylic acids according to the number of carboxyl, groups present in the molecule. For example, the one –COOH group containing, hydrocarbons such as formic acid, acetic acid, propionic acid, lactic acid, malic acid,, benzoic acid etc. are called monocarboxylic acids whereas the two –COOH groups, containing compounds such as oxalic acid, succinic acid, adipic acid, fumeric acid,, malic acid, tartaric acid phthalic acid etc. are called dicarboxylic acids similarly like, citric acid contains three -COOH group and termed as tri-carboxylic acid. The long, chain monocarboxylic acids are also known as fatty acids such as stearic acid, palmitic, acid, oleic acid etc. The general chemical formula of aliphatic carboxylic acids is, CnH2n+1COOH., , 6.3 NOMENCLATURE OF CARBOXYLIC ACIDS, In IUPAC system, carboxylic acids are named by replacing the suffix “–e” of the, corresponding alkane with “-oic acid”. It is not necessary to indicate the position of the, -COOH group because this group will be at the end of the parent chain and its carbon is, assigned as C-1. The common names and IUPAC names for some straight chain, saturated carboxylic acids are given in Table-6.1., , Table 6.1–Common names and IUPAC names of some straight chain saturated, carboxylic acids, Carboxylic acids, , Common name, , IUPAC name, , HCOOH, , formic acid, , methanoic acid, , CH3COOH, , acetic acid, , ethanoic acid, , UTTARAKHAND OPEN UNIVERSITY, , Page 181
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6.4 STRUCTURES AND BONDING, The carboxylic group (-COOH) in a carboxylic acid is constituted by a carbonyl group, (C=O) and a hydroxyl group (-OH). The carboxyl carbon atom is double bonded with, one oxygen atom and single bonded with another oxygen atom in a carboxylic group as, shown in figure:, , O, , carbonyl group, OH, , hydroxyl group, , The carboxylic acids can be represents by R-COOH or R-CO2H. The carboxylic carbon, in a carboxylic acid is bonded with three functional groups, therefore the carboxylic, carbon is sp2 hybridized and hence the carboxylic group has a planer structure with, bond angles of approximately 120º. In a carboxylic group, the C=O bond length is, shorter than the bond length between C-O. One half filled un-hybridized p-orbital of the, carbon and the un-hybridized p-orbital of the oxygen atom undergo sideways overlap., This results in the formation of the delocalized p-electron cloud. This is confirmed by, the C-O single bond length in formic acid being shorter than the C-O bond length in, ethanol. The oxygen is more electronegative than either carbon or hydrogen therefore, the C-O and O-H bonds are polar., , The carboxyl group has the following resonating structures:, , UTTARAKHAND OPEN UNIVERSITY, , Page 185
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ORGANIC CHEMISTRY-II, , BCHCH-202, , The third resonance structure (III) has all atoms with their full quota of electrons and, thus is more stable and more important contribution to the resonance hybrid than the, second structure (II) in which the positively charged carbon atom has only six electrons, in its valence shell. Thus in two important resonance structures [I] and [III] the carboxyl, carbon is electrically neutral. The carboxyl group is also polar due to resonance, structures [II] and [III]., , 6.5 PHYSICAL PROPERTIES, 1. Physical state, Lower members (C1-C3) are colorless liquids having pungent smell. C4-C9 members are, colorless oily liquids having an odor like goat butter. Higher members (C10 onwards), are colorless, odorless waxy solids., , 2. Hydrogen bonding, The intermolecular hydrogen bonding occurs in carboxylic acids. The two molecules of, carboxylic acids are associated by hydrogen bonding into dimers (pairs of molecules) in, liquid state or gaseous state. The boiling points and solubility of carboxylic acids are, associated with hydrogen bonding., , 3. Boiling point, , UTTARAKHAND OPEN UNIVERSITY, , Page 186
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Carboxylic acids have higher boiling points than the organic compounds like, alcohols,, ethers, aldehydes, or ketones of similar molecular weight. For example, acetic acid has, higher boiling point (118°C) than the 1-propanol (97°C) although the two have similar, molecular weights (60.1). Similarly, the butanoic acid and 1-pentanol have similar, molecular weights (MW 88.1), but the boiling point of butanoic acid (163 ºC) is more, than that of 1-pentanol (137 ºC). Because the two molecules of a carboxylic acid form, two hydrogen bonds with each other while two alcohol molecules can only form one, hydrogen bond. The boiling points of carboxylic acids increase with increase in, molecular weight., , 4. Solubility, The C1-C4 members are more soluble in water. This is due to the ability of the –COOH, group to form hydrogen bonds with water molecules. Due to strong H……. bonding,, carboxylic acids are more soluble in water than alcohols, ethers, aldehydes, or ketones, of comparable molecular weight. The solubility of a carboxylic acid in water decreases, as the molecular weight of carboxylic acids increases. This is due to, a carboxylic acid, consists two different polarities: a polar hydrophilic carbonyl group and a non polar, hydrophobic hydrocarbon chain. The hydrophilic carbonyl group increases water, solubility whereas hydrophobic hydrocarbon chain decreases water solubility., Therefore, C5 members are partly soluble and the higher carbon chain members are, insoluble in water, but readily soluble in ethanol, ethers and benzene., , 6.6 ACIDITY OF CARBOXYLIC ACIDS AND EFFECT OF, SUBSTITUENTS ON ACID STRENTH, A carboxylic acid can ionize in water into carboxylate ion and hydronium ion as:, R-COOH + H2O ⇌ RCOO- + H3O+, The, , equilibrium, , constant, , K, , for, K=, , given, , equation, , can, , be, , expressed, , as:, , [RCOOି ][Hଷ Oା ], [RCOOH][Hଶ O], , UTTARAKHAND OPEN UNIVERSITY, , Page 187
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ORGANIC CHEMISTRY-II, , BCHCH-202, , The carboxylate anion is also stabilized by resonance like carboxylic acid. The, stabilization of the anion is much greater than that of the neutral carboxyl group. In the, carboxylate anion the C-O bonds are of equal length and the two contributing structures, have equal weight in the hybrid., , 2. Effect of substituent’s on acidity of carboxylic acids:Substituent affects on the acidity of carboxylic acids by affecting the stability of, carboxylate anion. A substituent that stabilizes the carboxylate anion promoted the, dissociation and results in a stronger acid. Substituents on the α-carbon atom are most, effective in order to increase in acid strength., , Electron withdrawing groups such as -NO2, -CN etc. enhance the acid strength of a, carboxylic acid due to increase the stability of carboxylate anions through the, delocalization of negative charge by inductive or resonance effects. However the, electron releasing groups such as alkyl groups reduce the acidic strength of carboxylic, acids., For example, p-nitrobenzoic acid (pKa 3.41) is stronger acid than p-toluic acid (pKa, , 4.36) because the p-nitrobenzoic acid has an electron withdrawing –NO2 substituent, while the p-toluic acid has an electron releasing –CH3 substituent. The –NO2 group has, a larger effect in ortho and para positions than in meta position., , UTTARAKHAND OPEN UNIVERSITY, , Page 190
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6.7 PREPARATION OF CARBOXYLIC ACIDS, The carboxylic acids can be synthesized by various methods as follow:-, , 1. By the oxidation of primary alcohols and aldehydes, Carboxylic acids can be prepared by the oxidation of primary alcohols and aldehydes, with acidic KMnO4, or acidic K2Cr2O7., , For example:, , 2. From Koch reaction, Koch reaction is an organic reaction used to convert olefins into tertiary carboxylic, acids. In this reaction alkenes are treated with carbon monoxide and hydrogen in, presence of strong mineral acids like phosphoric acid or hydrogen fluoride to form the, tertiary carboxylic acids., , 3. By the oxidation of alkyl benzenes, Aromatic carboxylic acids may be formed by the oxidation of alkyl benzene with, K2Cr2O7, or acidic or alkaline KMnO4., , UTTARAKHAND OPEN UNIVERSITY, , Page 192
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ORGANIC CHEMISTRY-II, , BCHCH-202, , When toluene is heated with KMnO4, it is oxidized to benzoic acid., , Similarly, the isopropyl benzene is oxidized into benzoic acid with alkaline KMnO4., , Terephthalic acid can be obtained by the oxidation of p-xylene with acidic K2Cr2O7., , 4. By the hydrolysis of cyanides or nitriles, Alkyl halides react with sodium cyanide in SN2 displacement to form a nitrile which on, hydrolysis converted into carboxylic acid. The cyano group contains a hydrogen bond, which under acid hydrolysis converted into carboxylic group., , UTTARAKHAND OPEN UNIVERSITY, , Page 193
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Carboxylic acids can be prepared by the hydrolysis of esters either in acidic or alkaline, medium. For example, the acetic acid is formed by the hydrolysis of ethyl acetate in, acidic conditions., , 7. By the hydrolysis of acid derivatives viz. acyl chloride, acid anhydride, esters, and amides, The acid derivatives on hydrolysis with acid or alkali form corresponding carboxylic, acids., , (i) By the hydrolysis of acyl halides, Acid chlorides are hydrolyzed with water to parent carboxylic acids., , COCl, , COOH, +, , H2O, , +, , HCl, , (ii) By the hydrolysis of acid anhydride, Acid anhydrides are hydrolyzed with water to acids., O, , O, , O, -, , R, , C, , O, , C, , O, , Acid anhydrides, , R, , 1.H2O/OH, 2. H+, , UTTARAKHAND OPEN UNIVERSITY, , 2R, , C, , OH, , Carboxylic acid, , Page 195
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (iii) By the hydrolysis of esters, Esters are hydrolyzed to carboxylic acids in presence of an acid., , (iv) By the hydrolysis of amide, Acid amides are not easily hydrolyzed with water, but hydrolyzed easily on heating, with dilute acids or alkalies., , 6.8 REACTIONS OF CARBOXYLIC ACIDS, The carboxylic acids are reactive organiccompounds because of –OH and –CO group, and undergo many reactions some of ther are as follow., , (1) α-Halogenation of aliphatic acids: Carboxylic acids undergo halogenation with, chlorine or bromine in the presence of small amount of red phosphorus form α-halo or, , β-haloacids. The reaction is known as Hell Volhard Zelinsky reaction. In this reaction a, carboxylic acids containing an α-hydrogen atom is replaced by a chlorine or bromine, atom to form an α-halo carboxylic acid. The general reaction is as:, , UTTARAKHAND OPEN UNIVERSITY, , Page 196
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (Where, X= Cl, Br), Bromination of acetic acid is a good example of this reaction., , Mechanism: The stepwise mechanism is as follow of HVZ reaction, Step 1: Phosphorus reacts with bromine to form phosphorus tribromide, and in the first, step this converts the carboxylic acid into an acyl bromide., , Step 2: The acyl bromide then tautomerizes to the enol form which subsequently, attacks the halogen molecule to form a α-halo acyl halide. Water hydrolysis yields the, final α-halo carboxylic acid product., O, R CH, , C, , Br, , - H+, , O, , OH, R CH, , C, , R CH, , Br, , C, , H, Br, , H, acyl halide, Br, O, , O, R CH, , C OH, , H2O, , Br, alpha bromo carboxylic acid, , UTTARAKHAND OPEN UNIVERSITY, , Br, , R CH, , C, , Br, , Br, , Page 197
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Higher carboxylic acids are also reduced to alcohols by hydrogen in presence of copper, chromium oxide. This reaction is used to prepare detergents such as sodium lauryl, sulphate from lauryl alcohol., , Carboxylic acids cannot be reduced by H2/Ni, or Na/C2H5OH, or NaBH4, or catalytic, hydrogenation., , b. Reduction by HI: Carboxylic acids can be reduced to either primary alcohols or, alkanes depend upon the reducing agent involve in reaction, , (ii) Decarboxylation reaction: When an anhydrous sodium salt of a fatty acid is heated, with sodalime (NaOH + CaO) or Cu/ quinoline, it loses carbon dioxide to form an, alkane. This reaction is known as decarboxylation reaction. The general reaction is as:, RCOONa, , NaOH + CaO, Heat, , R, , H, , + CO2, , Simple copper salts such as copper chromate, copper hydroxide or copper carbonate can, also be used in decarboxylation of aliphatic and aromatic acids., , Aromatic carboxylic acids also react with sodalime to give benzene., , (iii) Hunsdiecker reaction: Silver salt of fatty acids on heating with a halogen (Cl or, Br) undergo decarboxylate halogenations give alkyl or aryl halides. The general, reaction is as:, , UTTARAKHAND OPEN UNIVERSITY, , Page 199
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (iii) Formation of esters: Carboxylic acids react with alcohols to form esters in, presence of concentrated H2SO4. This reaction involves the replacement of -OH group, by –OR group of alcohol or phenol and also known as Fischer-speier esterification. For, example, ethanoic acid reacts with ethanol to form ethylethanoate., , Esters can also be prepared by the action of the ethereal solution of diazomethane on, carboxylic acid., , Esters can also be prepared by the reaction of silver salt of acids on alkyl halides., , (iv) Formation of amides, Carboxylic acids react with ammonia to form ammonium salts which on heating lose, water molecule to form amides., , ., , UTTARAKHAND OPEN UNIVERSITY, , Page 203
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Hydrogen bonding, H, O, , O, , O, , C, , C, , C, , R, , CH2, , O, , -Keto acid, , R, , O, , +, CH3, , C, O, , Ketone, , Note: Simple copper salts such as copper hydroxide and copper carbonate can also be, used in decarboxylation of aliphatic and aromatic acids. For example:, , 6.10 METHODS OF FORMATION AND CHEMICAL, REACTIONS OF HALO ACIDS, Hydroxy acids, halo acids, amino acids and nitro acids are the derivatives of monocarboxylic acids and known as substituted carboxylic acids., , 6.10.1 PREPARATION OF HALO ACIDS:, 1. Hell Volhard Zelinski reaction: Aliphatic carboxylic acids on reaction with, bromine in the presence of phosphorous produce α- halo acids. This reaction is known, as Hell Volhard Zelinski reaction., , 2. By hydroxy acids: α-halo acids can be obtained by the treatment of α- hydroxy acids, with HCl or HBr., , UTTARAKHAND OPEN UNIVERSITY, , Page 205
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6.10.2 CHEMICAL REACTIONS OF HALO ACIDS:, Halo acids show the similar properties as carboxylic acids. Halo acids are also gives the, reactions of halogen group. The main reactions of halo acids are as follows:, , 1. Acidic strength: The halo acids are more acidic than carboxylic acids because, halogens are more electronegative than other atoms therefore a halogen atom withdraws, the electron pairs towards it and help to release the proton; since the halo acids are more, acidic than the normal acids., , H O, CH3, , C, , H O, , C O H, , CH3, , Cl, , C, , C O, , +, , H, , Cl, , 2. Reaction due to halogen atom, (i) Reaction with alkali; α-halo acids undergo alkaline hydrolysis form the α-hydroxy, acids., , CH3, , CH, , COOH, , + AgOH, , CH3, , Br, , CH, , COOH + AgBr, , OH, , 2-Bromopropanoic, acid, , Lactic acid, , While, β-halo acids on reaction with alkali form β-hydroxy acid and α, β-unsaturated, acid., , CH2ClCH2COOH, -Chloropropionic, acid, , NaOH, , CH2(OH)CH2COOH, -Hydroxy propionic, acid, , UTTARAKHAND OPEN UNIVERSITY, , H2O, , CH2, , CHCOOH, , Acrylic acid, , Page 207
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 1. From chlorohydrins: β-hydroxypropionic acid can be produced by the reaction of, ethylene chlorohydrins with potassium cyanide followed by hydrolysis., , 2. By the action of nitrous acid: β-hydroxypropionic acid is prepared by the action of, nitrous acid on β-aminopropionic acid in presence of sodium nitrite and hydrochloric, acid form lactic acid., , 3. By the oxidation of 1,3-dihydroxy compounds: β-Hydroxypropionic acid is, obtained by the reaction of 1,3-propyleneglycol with oxygen in presence of dilute nitric, acid., , 6.11.1 PHYSICAL PROPERTIES OF HYDROXY ACIDS:, 1. Physical state: Most of the hydroxy acids occur naturally and have several important, biological properties. They are colorless, crystalline solids or syrupy liquids. Hydroxy, acids are more acidic than normal carboxylic acids., , 2. Solubility: The hydroxyl derivatives are containing –OH and -COOH groups which, form hydrogen bond with water, therefore they are more soluble in water than the, corresponding carboxylic acids., , 3. Boiling points: The boiling or melting points of hydroxyl acids are also higher than, the corresponding carboxylic acids., , UTTARAKHAND OPEN UNIVERSITY, , Page 211
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6.11.2 PREPARATION AND CHEMICAL PROPERTIES OF, HYDROXY ACIDS:, The method of preparation, physical and chemical properties of some of the individual, hydroxyl acids alongwith their uses are being described as follow., , A. MALIC ACID, , Malic acid is an organic compound with the molecular formula C₄H₆O₅. It is also, known as hydroxyl butanedioic acid. It is a dicarboxylic acid that is made by all living, organisms, contributes to the pleasantly sour taste of fruits, and is used as a food, additive. Malic acid is a colorless crystalline solid, soluble in water and alcohol but, sparingly soluble in ether, it melts at 130 ºC. Malic acid contains one asymmetric, carbon, hence it exists in two optically active (two stereoisomeric forms: L- and Denantiomers) and one inactive form, though only the L-isomer exists naturally., , Preparation of malic acid: Malic acid can be prepared by the following methods:, 1. By the action of nitrous acid on α-amino succinic acid (aspartic acid)., Malic acid can be obtained by the reaction of nitrous acid on Aspartic acid., , UTTARAKHAND OPEN UNIVERSITY, , Page 212
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. By the partial reduction of tartaric acid: Malic acid can be prepared by the, reduction of tartaric acid with HI., , 3. From bromosuccinic acid: When bromosuccinic acid is treated with moist silver, oxide, malic acid is obtained., , Chemical properties of malic acid: Malic acid posses following chemical properties., 1. Action of heat: Malic acid undergoes dehydration on heating to form maleic, anhydride., , 2. Oxidation with KMnO4: On oxidation with KMnO4 malic acid forms oxalacetic, acid, which exits in keto-enol tautomerism., , UTTARAKHAND OPEN UNIVERSITY, , Page 213
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 3. Oxidation with H2CrO4: On oxidation with chromic acid, malic acid converts into, malonic acid., , 4. Reduction: Malic acid reduces with HI to form succinic acid., , Uses: Malic acid is used:, 1., , In the preparation of several esters and salts., , 2., , As a substitute of citric acid in drinks., , 3., , In the preparation of medicine of sure throat., , B. TARTARIC ACID, , Tartaric acid, HOOC(CHOH)2COOH, is a dicarboxylic acid, found in many plants, particularly tamarinds and grapes. Tartaric acid is also known as α,α′-dihydroxy, succinic acid (IUPAC name : 2,3-dihydroxybutanedioic acid). It is a colorless, crystalline solid, soluble in water and alcohol, and melt at 170 ºC. It has an acidic taste., Tartaric acid has two identical asymmetric carbon atoms and exists in four, stereoisomeric forms dextro, laevo, meso and racemic:, , UTTARAKHAND OPEN UNIVERSITY, , Page 214
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 1. Dextrorotatory tartaric acid (d-tartaric acid) is found naturally in grapes berries,, plums and several other fruits., 2. Levorotatory tartaric acid (l-tartaric acid) is obtained chiefly by resolution of racemic, tartaric acid., 3. Racemic tartaric acid (an equal mixture of d- and l-tartaric acid) is prepared, commercially by the molybdenum- or tungsten-catalyzed oxidation of maleic, anhydride with hydrogen peroxide., , Preparation of tartaric acid: Tartaric acid can be prepared by the following general, methods:, , 1. From glyoxal: On treatment with hydrogen cyanide, glyoxal produces glyoxal, cynohydrin which on hydrolysis gives tartaric acid., , 2. From Kiliani-Fisher synthesis: Kiliani- Fisher synthesis is one of the methods to, increase no of carbons in copounds. Tartaric acid can also be formed from, glyceraldehydes., , 3. From α, α'-dibromosuccnic acid : Both (±) and meso tartaric acids are prepared by, boiling α, α'-dibromosuccnic acid with moist silver oxide., , UTTARAKHAND OPEN UNIVERSITY, , Page 215
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 4. By the oxidation of fumeric acid: Tartatic acid can be prepared by the oxidation of, fumeric acid with alkaline KMnO4., , Chemical properties of tartaric acid: The chemical properties of tartaric acids are as, under., , 1. Oxidation: With mild oxidizing agents tartaric acid yields tartonic acid while with, strong oxidizing agents, tartaric acid forms oxalic acid., , However, on oxidation with Fenton’s reagent (alkaline H2O2 + FeSO4), tartaric acid is, oxidized into dihydroxy maleic acid., , 2. Reduction: Tartaric acid with HI is reduced into malic acid and then to succinic acid., , With HBr, the tartaric acid is reduced to bromosuccinic acid., , UTTARAKHAND OPEN UNIVERSITY, , Page 216
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 3. Salt formation: Tartaric acid forms two series of salts with the reactions of alkali., , 4. Action of heat: When tartaric acid is heated at 150ºC, it decomposes into tartaric, anhydride., , On strong heating, it decomposes into pyruvic acid with the evolution of CO2., , Uses: Tartaric acid is used:, 1., , In the preparation of baking powder and effervescent beverages., , 2., , In mirror silvering in the form of sodium potassium tartrate., , 3., , As mordant in dying and calico printing., , C. CITRIC ACID, , UTTARAKHAND OPEN UNIVERSITY, , Page 217
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ORGANIC CHEMISTRY-II, , BCHCH-202, , On heating with fuming sulphuric acid at 150 ºC, citric acid gives acetone dicarboxylic, acid., , 3. Reaction with acetic anhydride: Citric acid produces monoacetyl derivatives., , 4. Reduction: In presence of hydrogen iodide citric acid reduced to tricarballylic acid., , Uses: Citric acid is used:, 1., , As flavor compound in the preparation of synthetic fruit drinks., , 2., , As laxative in form of magnesium citrate., , 3., , As solvent in polymer synthesis., , 4., , As an iron supplement in the form of ferric ammonium citrate., , 5., , As mordant in printing and dying., , UTTARAKHAND OPEN UNIVERSITY, , Page 221
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6.12 SUMMARY, The unit containing organic compounds carboxylic acids with –OH and –COOH group, together can be summarized as: The carboxylic acids are known as mono, di, tri, or, polycarboxylic acids according to number of carboxyl groups present in the molecule., Long chain monocarboxylic acids are also known as fatty acids such as stearic acid,, palmitic acid, oleic acid etc. The carboxylic acids can be represented by–RCOOH or –, RCO2H. In IUPAC system, monocarboxylic acids are named by replacing the suffix “–, , e” of the corresponding alkane with “-oic acid”, dicarboxylic acids named by add the, suffix –dioic acid to the name of the parent alkane containing both carboxylic groups., Aromatic carboxylic acids are named by adding the suffix "-carboxylic acid" to the, name of a parent hydride. The carboxylic carbon in a carboxylic acid is bonded with, three functional groups, therefore the carboxylic carbon is sp2 hybridized and hence the, carboxylic group has a planer structure with bond angles of approximately 120օ.The, carboxylic acids are associated by hydrogen bonding into dimers (pairs of molecules) in, liquid state or gaseous state. Carboxylic acids have higher boiling points than other, hydrocarbons such as alcohols, ethers, aldehydes, or ketones of comparable molecular, weight. The C1-C4 members are more soluble in water. This is due to the ability of the –, COOH group to form hydrogen bonds with water molecules. The C5 members are, partly soluble, and the higher carbon chain members (C10 onwards) are insoluble in, water, but readily soluble in ethanol, ethers and benzene.The carboxylic acids are weak, acids, their acidic strength decreases with increase in molecular weight. Electron, withdrawing groups enhance the acid strength due to increase the stability of, carboxylate anions through the delocalization of negative charge by inductive or, resonance effects. However the electron releasing groups reduce the acidity of, carboxylic acids. The carboxylic acids (pKa 4-5) are stronger acids than alcohols, (pKa 16-18) because of delocalization of the negative charge of the carboxylate anion, through resonance and the electron withdrawing inductive effect of the carbonyl group., The carboxylic acids can be prepared, by various methods viz; by the oxidation of, primary alcohols and aldehydes with acidic KMnO4 or acidic K2Cr2O7. By alkenes on, treatment with carbon monoxide and steam in presence of phosphoric acid.By the, oxidation of alkyl benzene with K2Cr2O7 or acidic or alkaline KMnO4. By the reaction, of Grignard’s reagents on carbon dioxide. By the hydrolysis of esters and other, , UTTARAKHAND OPEN UNIVERSITY, , Page 222
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ORGANIC CHEMISTRY-II, , BCHCH-202, , functional derivatives either in acidic or alkaline medium. The carboxylic acids undergo, halogenations with chlorine or bromine, are reduced to alcohol with a suitable reducing, agent like lithium aluminium hydride (LiAlH4) can be decarboxylated, undergo Kolbe’s, electrolysis, release hydrogen gas while reacting with active metals such as K, Ca,, Mg.The carboxylic acids react with alkalis like sodium hydroxide to form salts and, water.This unit also describe functional derivatives like acyl chlorides, esters and, amides, anhydrides and their methods of preparation by various methods along with, physical and chemical reactions. Hydroxy acids like malic acid, tartaric acid and citric, acids are very important compounds. This unit also makes the readers aware about the, methods of preparations, properties and uses of these hydroxyl acids., , 6.13 TERMINAL QUESTIONS, Section-A, Q.1 Long answered questions: Answer the following questions, 1. What are carboxylic acids? Describe the structure and nomenclature of aliphatic, and aromatic carboxylic compounds., 2. What are carboxylic acids? Give the general methods of preparation of, carboxylic acids., 3. Describe the reduction and decarboxylation reactions of carboxylic acids., 4. What are halo acids? Give the general methods of preparation and chemical, properties of halo acids., 5. What are hydroxyl acids? Give the general methods of reparation and properties, of malic acid., 6. Describe the general methods of preparation, physical and chemical properties of, tartaric acid., 7. How is citric acid synthesized? Describe the important chemical properties of, citric acid., , UTTARAKHAND OPEN UNIVERSITY, , Page 223
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Section-B, Q.2 Short answered questions, 1. How can you synthesize carboxylic acids from cyanides?, 2. Write a short note on the acid strength of carboxylic acids., 3. Write the physical properties of carboxylic acids., 4. Why the monochloroacetic acid is stronger than acetic acid?, 5. Explain benzoic acid is more acidic than phenol., 6. Compare the acidic strength of acetic acid and halo acids., 7. Give the mechanism of Hell Volhard Zelinsky reaction., 8. How can you obtain halo acids from Hell Volhard Zelinsky reaction?, 9. Give the mechanism of decarboxylation., 10. How can you synthesize esters and amides from carboxylic acids?, 11. How can you prepare succinic acid from tartaric acid?, 12. Give the method of preparation of hydroxyl acids., 13. How can you convert tartaric acid into oxalic acid, and tartaric acid into malic acid?, , 14. How will you obtained?, a. Carboxylic acids from acyl chlorides, b. Carboxylic acids from aldehydes, c. Carboxylic acids from alkyl benzene, d. Carboxylic acids from nitriles, , 15. How can you convert?, a) Carboxylic acids into halo acids, b) Carboxylic acids into alcohols, c) Carboxylic acids into alkanes, d) Carboxylic acids into acid anhydrides, , UTTARAKHAND OPEN UNIVERSITY, , Page 224
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Section-C, Q.3 Multiple choice questions(MCQ), 1. Which functional group is present in a carboxylic acid?, (a) -COOH, , (b) –NH2, , (c) -RCOOR’, , (d) –OR’, , 2. Which one of the followings is a monocarboxylic acid?, (a) Oxalic acid, , (b) Succinic acid, , (c) Formic acid, , (d) Citric acid, , 3. What is the IUPAC name of HOOC (CHOH)2 COOH ?, (a) 2-Hydroxypropionic acid, , (b) 2, 3-Dihydroxybutanedioic acid, , (c) 2-Hydroxybutanedioic acid, , (d) Butanedioic acid, , 4. Carboxylic acids are more soluble in water than alcohols and ethers due to, (a) Their high molecular weight, , (b) Hydrogen bonding, , (c) More reactive carboxyl carbon, , (d) Their acidic charecter, , 5. Carboxylic acid and alcohols both are formed hydrogen bonding with water but why, carboxylic acids have higher boiling points than alcohols?, (a) Because acids are more reactive than alcohols., (b) Because carboxylic acids are weak acids., (c) Because alcohols are not ionized completely., (d) Because the two molecules of a carboxylic acid form two hydrogen bonds., 6. Which of the following is the strongest acid?, (a) CH2ClCOOH, , (b) CH2BrCOOH, , (c) CH2FCOOH, , (d) CH2ICOOH, , 7. The weakest acid among the following is, (a) Cl3CCOOH, , (b) Cl2CHCOOH, , (c) ClCH2COOH, , (d) CH3COOH, , 8. Primary alcohols are oxidized with acidic KMnO4 into, (a) Carboxylic acid, , (b) Amide, , (c) Acid anhydride, , (d) Alcohols, , UTTARAKHAND OPEN UNIVERSITY, , Page 225
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 19. On reduction with strong oxidizing agent tartaric acid forms, (a) Maleic acid, , (b) Succinic acid, , (c) Oxalic acid, , (d) Citric acid, , 20. Formation of α-chloropropionic acid to α-aminopropionic acid is an example of, (a) Electrophilic substitution, , (b) Ammonolysis, , (c) Friedel Craft acylation, , (d) Nucleophilic substitution, , 21. What is the reagent for the following reaction?, , (a) LiAlH4, , (b) KMnO4, , (c) NaOH, , (d) HI, , 22. A primary alcohol can be oxidized to which of the following?, (a) An aldehyde, , (b) A ketone, , (c) A carboxylic acid, , (d) A hemiacetal, , 23. α- bromination of carboxylic acid by a mixture of Br2 and PBr3 is called, (a) Michael reaction, , (b) Hell-Volhard Zelinskii reaction, , (c) Friedel Craft acylation, , (d) Claisen- condensation reaction, , 24. Which of the following acids is used in making baking powder?, (a) Oxalic acid, , (b) Citric acid, , (c) Tartaric acid, , (d) Lactic acid, , 25. Acid present in lemon is, (a) Oxalic acid, , (b) Citric acid, , (c) Tartaric acid, , (d) Lactic acid, , UTTARAKHAND OPEN UNIVERSITY, , Page 227
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6.14 ANSWERS (MCQ):, 1., , (a), , 2., , (c), , 3., , (b), , 4., , (b), , 5., , (d), , 6., , (c), , 7., , (d), , 8., , (a), , 9., , (c), , 10., , (b), , 11., , (c), , 12., , (a), , 13., , (d), , 14., , (b), , 15., , (c), , 16., , (d), , 17., , (a), , 18., , (b), , 19., , (c), , 20., , (d), , 21., , (a), , 22., , (c), , 23., , (b), , 24., , (c), , 25., , (b), , 6.10 REFERENCES, 1. B.S. Bahal, A. Bahal. Advanced Organic Chemistry. S. Chand & Company Ltd., Ram Nagar, New Delhi 1993, 2. I.L Finar, Organic Chemistry Vol. 2., 5th edition, ELBS & Longman group Ltd.,, 1974.., 3. R.T.Morrison and R.N.Boyd Organic Chemistry, 6th edition, Prentice Hall Private, Ltd. 1997., 4. Clayden,Greeves,Warren and Wothers Organic Chemistry 2nd edition 2012, Oxford, University Press, 5.Jagdamba Singh and L.D.S.Yadav, Organic Chemistry vol. I, 8th edition-2013, Pragati Prakashan Pub., 6. F.A.Carey and R.J.Sundberg Advanced Organic Chemistry, Plenum Pub. 5th, Edition, 2007, 7.S.M. Mukherji and S.P. Singh, Reaction Mechanism in Organic Chemistry, Trinity, Press,2016, 8. B.S. Bahal, A. Bahal. Advanced Organic Chemistry. S. Chand & Company Ltd., Ram Nagar, New Delhi 1993, , UTTARAKHAND OPEN UNIVERSITY, , Page 228
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT-7 FUNCTIONAL DERIVATIVES OF, MONOCARBOXYLIC ACIDS, CONTENTS:, 7.1 Objectives, 7.2 Introduction, 7.3 Structure and nomenclature of acid chlorides, esters, amides and acidhydrides, 7.4 Relative stability of acyl derivative, 7.5 Physical properties, 7.6 Preparation of carboxylic acid derivatives, 7.7 Chemical reactions of carboxylic acid derivatives, 7.8 Mechanism of esterification and hydrolysis (acidic and basic), 7.9 Summary, 7.10 Terminal Question, 7.11 Answers (MCQ), 7.12 References, , 7.1 OBJECTIVES, The objectives of this unit are to study carboxylic acid derivatives viz. acid halides, acid, anhydrides, esters and amides using IUPAC naming system. Describe the structure; acid, strength and reactivity of carboxylic acid derivatives.To synthesize carboxylic acid, derivatives: acyl halides, acid anhydrides, esters, and amides. Describe the physical, properties of carboxylic acid derivatives. To describe the chemical properties of, carboxylic acid derivatives. To describe the mechanism of estrification, and acidic and, alkaline hydrolysis., , 7.2 INTRODUCTION, The most important functional derivatives of carboxylic acids are acyl chlorides, (RCOCl), acid anhydrides ((RCO)2O), esters (RCOOR’ where R and R’ may be same, or different), and amides (RCONH2) which are obtained by the replacement of -OH part, of carboxyl group of acids by –Cl, -OCOR, -OR' or -NH2 groups respectively., , UTTARAKHAND OPEN UNIVERSITY, , Page 229
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 7.3 STRUCTURE AND NOMENCLATURE OF ACID, CHLORIDES, ACID ANHYDRIDES, ESTERS, AMIDES, AND ANHYDRIDES, A carboxylic group contains a carbonyl group (C=O) and a hydroxyl group (-OH), bonded to the carbonyl carbon. The structure of carboxylic group is:, , O, , sp, , 2, , C OH, The carboxylic carbon in a carboxylic acid is bonded with three functional groups,, therefore the carboxylic carbon is sp2 hybridized and hence the carboxylic group has a, planer structure with bond angles of approximately 120օ. Carboxylic acid derivatives, are the organic compounds that are synthesized from the carboxylic acids by the, replacement of –OH group of carboxyl group by –Cl, -OCOR (acyloxy group), -OR’, (alkoxy group) or –NH2 groups., , UTTARAKHAND OPEN UNIVERSITY, , Page 230
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Where, Z may be chlorine atom, acyloxy group, alkoxy group or amide group., The four important carboxylic acid derivatives are acid chlorides, acid anhydrides,, esters and amides. These acid derivatives are distinguished from each other by the, group attached to the carbonyl carbon atom., , Hence, the carboxylic acids and their derivatives contain a sp2 hybridized carbonyl, group which consists an O atom bonded to a C atom via a double bond in a planar, model with bond angles of approximately 120º. In carboxylic acids derivatives, the, hetero atom group (-Cl, N, or O) is connected to the carbonyl carbon via a σ bond. The, resonance interaction of the carbonyl group with the lone pair of the adjacent, heteroatom has important implications on the reactivity., , Polarity of carboxylic acid derivatives: Structurally, the carboxylic acid and their, derivatives differ by only the substituent Z attached to the carboxylic carbon as shown, in their structures. Carboxylic acid and their derivatives have a common group i.e., acyl, group (R-C=O). The chemical reactions of those organic compounds containing an acyl, group depend on the nature of bond (polar or nonpolar) between the carbonyl carbon of, acyl group and the substituent (Z) attached to it. The organic compounds containing an, acyl group are called acyl compounds. On the basis of polarity, acyl compounds can be, classified into two types: nonpolar carbonyl compounds and polar acyl compounds., , The carbonyl carbon of acyl group in carbonyl compounds is attached directly to a, hydrogen atom or any other carbon atom. The carbon-carbon bond and carbon–, hydrogen bonds are non polar because the electronegativities of the carbon and, , UTTARAKHAND OPEN UNIVERSITY, , Page 231
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ORGANIC CHEMISTRY-II, , BCHCH-202, , HCONH2, , formamide, , methanamide, , CH3CONH2, , acetamide, , ethanamide, , C2H5CONH2, , propionamide, , propanamide, , C3H7CONH2, , butyramide, , butanamide, , C4H9CONH2, , valeramide, , pentanamide, , 7.4 RELATIVE STABILITY OF ACYL DERIVATIVES, Acid derivatives can be listed in order of their reactivity towards nucleophilic acyl, substitution as:, , The magnitude of the δ+ charge on the carbonyl carbon depends on the electron, releasing or electron attracting power of the substituent. The substituent groups of acid, chlorides and anhydrides have an ability to withdraw electrons from the carbonyl, carbon, making these derivatives more reactive than carboxylic acids. On the other hand, in esters and amides, the substituent (Z group) release electrons onto the carbonyl, carbon which makes these derivatives less reactive. The reactivity of the carboxylic, acid derivatives can be explained in details as:, , A. Acyl chlorides: The electron withdrawing inductive effect of an acyl chloride is not, stabilized by electron pair donation; the electron withdrawing inductive effect of, chlorine makes it more electrophilic and more reactive towards nucleophilic acyl, substitution., , UTTARAKHAND OPEN UNIVERSITY, , Page 234
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ORGANIC CHEMISTRY-II, , BCHCH-202, , B. Acid anhydrides: In acid anhydrides, the carbonyl group is better stabilized by, electron donation than acyl chlorides. Here electron pair orbital (2p) of oxygen, overlap with the orbital of carbonyl group but the presence of two carbonyl groups, create competition for the same electron pair. Thus, the extent of stabilization in, resonance is decreased., , C. Esters: The carbonyl group of esters is stabilized more effectively by the electron, pair of oxygen than acid anhydride. Because, only one carbonyl group is present in, esters, this increases the stability of carbonyl group of ester and decreases the, reactivity towards nucleophilic substitution than acid anhydrides., , D. Amides: Acid amides are less reactive towards nucleophilic substitution. This is, due to the positive charge on acyl carbon atom, which is so necessary for, nucleophilic substitution. They are at least 10 times less reactive than acyl, chlorides., , 7.5 PHYSICAL PROPERTIES, A. Acyl chlorides: The lower members are colorless, volatile liquid having irritating, smell. Higher members are colorless liquids. The boiling points of acid derivatives are, lower than that of carboxylic acids due to the absence of intermolecular hydrogen, bonding. They also fume in moist air., , UTTARAKHAND OPEN UNIVERSITY, , Page 235
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ORGANIC CHEMISTRY-II, , BCHCH-202, , B. Acid anhydrides: Acid anhydrides are colorless liquids or solids with irritating, smell. They are soluble in organic solvents, although the lower members are readily, soluble in water. They have higher boiling points than parent acids due to their larger, size., , C. Esters of acids: Esters are colorless liquids or solids having fruity or flowery odor., Low molecular weight esters are soluble in water. The solubility of esters decreases, with increase the molecular weight. All esters are soluble in organic solvents like, benzene, ethers etc. Ester do not form hydrogen bonding, so they have lower melting, and boiling points than corresponding carboxylic acids. Boiling points of normal chain, esters are higher than those of branched chain isomers., , D. Acid amides: Expect formamide (HCONH2 which is a liquid), all amides are, colorless crystalline solids. The intermolecular hydrogen bonding is associated in, amides, so their melting points are much higher than parent carboxylic acids. Lower, members of amides homologous series are water soluble., , 7.6 PREPARATION OF CARBOXYLIC ACID DERIVATIVES, (A) ACYL CHLORIDE: Acid chlorides are also known as acyl chlorides have the, general formula R-COCl. They are obtained by the replacement of a –OH group by a Cl atom. They can be formed by heating carboxylic acids or their salts with, phosphorous trichloride (PCl3), phosphorus penta chloride (PCl5), or thionyl chloride, (SOCl2)., , 1. From acids: Acyl chlorides are prepared by heating carboxylic acids with, phosphorous trichloride (PCl3), phosphorus penta chloride (PCl5), or thionyl chloride, (SOCl2)., , UTTARAKHAND OPEN UNIVERSITY, , Page 236
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. From salts: Acyl chlorides are prepared by the treatment of sodium salts of, carboxylic acids with phosphorous trichloride (PCl3) or thionyl chloride (SOCl2)., , (B) ACID ANHYDRIDE: Acid anhydrides are formed by the dehydration of, carboxylic acids. They are obtained by the elimination of one water molecule from the, two molecules of monocarboxylic acids. Ethanoic anhydride is the most common acid, anhydride. They can be prepared by the following general methods:, , 1. Dehydration of anhydrous acids: Acid anhydride can be obtained by heating, anhydrous acids in presence of a dehydrating agent like P2O5., , UTTARAKHAND OPEN UNIVERSITY, , Page 237
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. By heating acid chlorides with anhydrous salts of acid: Acid anhydride can be, prepared by heating an acid chloride with anhydrous sodium salts of a carboxylic acid., , 3. By heating sodium salts of carboxylic acids with acetic anhydride: Anhydrides of, higher acids can be obtained by heating sodium salts of carboxylic acids with acetic, anhydride., , 4. By the reaction of excess amount of anhydrous sodium salts of acid with, phosphorus oxy-chloride or thionyl chloride: Acid anhydrides are synthesized by, treating sodium salt of carboxylic acid with POCl3 or SOCl2., , (C) ESTERS OF ACIDS: Esters are carboxylic acid derivatives which are formed by, the replacement of hydroxyl (-OH) part of –COOH group by an alkoxy group (-OR)., They are found naturally in several plants, fruits and flowers. Orange, banana, apple,, pineapple, mango etc. are the chief source of esters. Oils, fats and waxes are also, , UTTARAKHAND OPEN UNIVERSITY, , Page 238
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ORGANIC CHEMISTRY-II, , BCHCH-202, , composed by the esters of higher fatty acids like stearic acid, palmitic acid, oleic acid, and cerotic acid etc. Esters can be formed by the following general methods:, , 1. By direct esterification: When an alcohol interacts with an acid in presence of a, suitable acid catalyst, esters are formed by the elimination of a water molecule. This, process is known as esterification., , CH3COOH + C6H5OH, Acetic acid, , Phenol, , H+, , CH3COOC6H5 + H2O, Phenyl acetate, , 2. By the action of alcohols on acid chlorides or anhydrides: Esters are prepared by, the nucleophilic substitution of acid chlorides or acid anhydrides with alcohols., , 3. By heating silver salts of carboxylic acids with alkyl halides : Esters are prepared, by the reaction of silver salt of acids on alkyl halides., , UTTARAKHAND OPEN UNIVERSITY, , Page 239
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 4. By the action of diazomethane on carboxylic acids: Methyl esters are prepared by, the action of the ethereal solution of diazomethane on carboxylic acid., , COOH, , COOCH3, +, , CH2N2, , ether, +, , N2, , benzoic acid diazomethane, 5. From ethers and carbon monoxide: When ether interacts with carbon monoxide at, 125-180 ºC under 500 atmospheric pressure in presence of boron trifluoride catalyst, an, ester is formed., , O, CH3, , O CH2CH3, , +, , CO, , heat, , CH3, , C OCH2CH3, , (D) ACID AMIDES: Amides are regarded as carboxylic acid derivatives in which the, hydroxyl group (-OH) is replaced by an amino group (-NH2). For example, the most, common amides are methanamide (HCONH2) and ethanamide (CH3CONH2). They, have the general formula R-CONH2. The acid amides can be prepared by the following, general methods:, , 1. Action of ammonia on acyl chloride, acid anhydride or ester: Acid amides can be, prepared by the acylation of ammonia with acyl chlorides, acid anhydrides or esters., , UTTARAKHAND OPEN UNIVERSITY, , Page 240
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. By heating ammonium salts of fatty acids: The ammonium salts of carboxylic, acids on heating give amides., , 3. Partial hydrolysis of cyanides: The partial hydrolysis of cyanides with, concentrated hydrochloric acid, polyphosphoric acid or alkaline peroxide produces, amides., , 4. Reaction of an acid chloride with an amine: Acid chlorides are converted into, primary, secondary and tertiary amides by the reaction with ammonia, primary amines, and secondary amines respectively., , UTTARAKHAND OPEN UNIVERSITY, , Page 241
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ORGANIC CHEMISTRY-II, COCl, , BCHCH-202, CONH2, , +, , NH3, , +, , HCl, , benzoic acid, , 7.7 CHEMICAL REACTIONS OF CARBOXYLIC ACID, DERIVATIVES, (A) ACYL CHLORIDE: Acyl chlorides are most reactive derivatives of carboxylic, acids. They easily undergo nucleophilc acyl substitutions to form acid anhydrides,, esters and amides. The most common acyl chlorides are methanoyl chloride (CHOCl), and ethanoyl chloride (CH3COCl). The acyl chlorides give the following chemical, properties:, , 1. Basic character: Acyl chlorides are very much less basic because the chlorine atom, is not effective at stabilizing a positive charge., , 2. Reduction: Acid chlorides get reduced to aldehydes by the action of hydrogen in, presence of Pd/BaSO4., , 3. Hydrolysis: Acid chlorides are hydrolyzed with water to parent carboxylic acids., , UTTARAKHAND OPEN UNIVERSITY, , Page 242
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 14. Friedel Craft’s reaction: Acyl chlorides on reaction with aromatic hydrocarbons in, presence of Lewis acid (AlCl3) in Friedel Craft acylation form aromatic ketones., COCH3, , Anhydride, + CH3COCl, , + HCl, AlCl3, Acetophenone, , Uses: Acyl chlorides are used in the preparation of acetic anhydride, acetamide and, acetanilide, and as acetylating agents in many reactions. They are also used in the, detection and determination of –OH, -NH2, , NH and, , functional, , groups, , in, , a, , molecule., , (B) ACID ANHYDRIDES: Acid anhydrides are less reactive than acyl chlorides, towards nucleophilic substitution. The most common acid anhydride is acetic, anhydride. The important chemical reactions of acetic anhydride are:, , 1. Hydrolysis: Acid anhydrides are hydrolyzed with water to acids., , 2. Alcoholysis: Acid anhydrides react with ethyl alcohol to produce esters., , 3. Ammonolysis: Ammonia rapidly reacts with acetic anhydrides to give acetamide., , 4. Action with primary amines: Primary amines react with acid anhydride to form, amides., , 5. Reduction: On reduction with LiAlH4, or Na and alcohol, acetic anhydrides produce, alcohols., , UTTARAKHAND OPEN UNIVERSITY, , Page 246
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6. Friedel Craft acylation: Acitic anhydrides on treatment with benzene in presence of, anhydrous AlCl3 form aromatic ketones., , 7. Action with phosphorous pentachloride: Acetic anhydride reacts with phosphorous, pentachloride to form acetyl chloride and phosphorous oxy-trichloride., , 8. Action of chlorine: Acid anhydride reacts with chlorine to form acetyl chloride and, monochloroacetic acid., , 9. Action with dry hydrogen chloride: On reaction with dry hydrogen chloride, acetic, anhydride forms acetyl chloride and acetic acid., , Uses: Acid anhydrides are used in the preparation of amyl acetate, aspirin, dyes also, acetate rayon. They are also used as acetylating agent., , (C) Esters: Esters are less reactive than acyl chloride and acid anhydrides. Methyl, methanoate (HCOOCH3) and ethyl ethanoate (CH3COOC2H5) are the most common, esters. They can be converted into carboxylic acid by acid or base hydrolysis, into, amides with ammonia and can be reduced into alcohols with LiAlH4., , 1. Hydrolysis: Esters are hydrolyzed to carboxylic acids in presence of an acid whereas, in presence of an alkali they produce sodium salts of carboxylic acids., , Acid hydrolysis:, , UTTARAKHAND OPEN UNIVERSITY, , Page 247
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Alkaline hydrolysis:, , 2. Action of ammonia: Esters slowly react with ammonia to form amides and alcohols., This process is called ammonolysis., , Mechanism:, , 3. Reduction: On reduction with LiAlH4 or Na and alcohol, esters produce alcohols., , 4. Halogenation: Esters on reaction with chlorine or bromine in presence of red, phosphorous give the α-halogenated esters (Hell Volhard Zelinsky reaction)., , 5. Claisen condensation: One molecule of an ester combines with second molecule of, that ester in presence of sodium alkoxide to give an aldehyde or an ketone. This, reaction is known as Claisen condensation., , UTTARAKHAND OPEN UNIVERSITY, , Page 248
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Uses: Esters are used as solvent in perfumes, plasticizers, gums, resins, cellulose,, paints, varnishes, oils and fats. They are commercially used in making artificial flavors, and essence., , (D) ACID AMIDES: Amides are least reactive derivatives of carboxylic acids. They, are also converted into carboxylic acid by acid or alkaline hydrolysis. They can be, dehydrated into nitriles. The important chemical reactions of acid amides are:, , 1. Amphoteric character: Amides are weak acids as well as weak base. They are most, basic than other derivatives because nitrogen is an effective donor of electrons in, comparison to oxygen. They are neutral to litmus., , (a) Basic property: Acetamide behaves as a base and reacts with hydrochloric acid to, produce a salt (acetamide hydrochloride)., , CONH2, +, , CONH2.HCl, HCl, , benzamide, , benzamide hydrochloride, , (b) Acidic property: Acetamide as an acid reacts with sodium (Na) or mercury oxide, (HgO) to form corresponding salts., , 2. Hydrolysis: Acid amides are not easily hydrolyzed with water, but hydrolyzed easily, on heating with dilute acids or alkalies., , Acid hydrolysis, , UTTARAKHAND OPEN UNIVERSITY, , Page 250
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6. Hoffmann’s bromamide or Hoffmann’s degradation reaction: Amides on, reaction with bromine and alcoholic potassium hydroxide form primary amines. This, reaction is known as Hoffmann bromamide or Hoffmann degradation reaction., RCONH2 + Br2 + 4KOH, Amide, , RNH2 + K2CO3 + 2KBr + 2H2O, Amine, , Uses: Amides are used as a solvent for several organic and inorganic compounds,, wetting agent, plasticizer in cloths etc. They are also used in making explosives and, leather tanning., , 7.8 MECHANISM OF ESTRIFICATION AND HYDROLYSIS, (ACIDIC AND BASIC), (a) ESTERIFICATION: When a carboxylic acid is treated with an alcohol in presence, of an acid catalyst, an ester is formed along with water. This reaction is known as, , Fischer esterification., , Mechanism: The sequential mechanism ofesterification under acidic condition is as, under:, , UTTARAKHAND OPEN UNIVERSITY, , Page 253
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (b) HYDROLYSIS: Esters are not hydrolyzed easily with water, but hydrolyzed, rapidly in acidic or alkaline medium. Both acid hydrolysis and alkaline hydrolysis are, the examples of acyl nucleophilic substitution reactions., , i. Acid hydrolysis: When esters are boiled with water in presence of a strong acid like, sulphuric acid or hydrochloric acid then carboxylic acids and alcohols are produced., , ii. Alkaline hydrolysis: When esters are boiled with an aqueous solution of a strong base, like sodium hydroxide then sodium salts of carboxylic acids and alcohols are formed., This reaction is known as saponification reaction., , (i) Mechanism of acid hydrolysis: The esters are hydrolysed in following steps., Step 1: Protonation of the ester carbonyl makes it more electrophilic., Step 2: The ‘O’ atom of water acts as a nucleophile which attacks on the, electrophilic C in the C=O group, with the electrons moving towards the oxonium ion,, creating the tetrahedral intermediate., , UTTARAKHAND OPEN UNIVERSITY, , Page 254
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Step 3: Deprotonate the oxygen that came from the water molecule to neutralize the, charge., , Step 4: The –OR′ group converts into a good leaving group by protonation, and R′OH, is eliminated., , Step 5: Deprotonation of the oxonium ion reveals the carbonyl C=O group in the, carboxylic acid product and regenerates the acid catalyst., , (ii) Mechanism of alkaline hydrolysis: In alkaline medium esters are hydrolysed in, following sequential steps., , Step 1: The hydroxide nucleophile attacks at the electrophilic carbon of the ester C=O,, and breaks the π bond to create a tetrahedral intermediate., , Step 2: This intermediate collapses to reform the C=O bond results the loss of, alkoxide (RO-) group., , Step 3: A very rapid equilibrium coexist where the alkoxide ion (RO-) acts as a base for, deprotonating the carboxylic acid., , UTTARAKHAND OPEN UNIVERSITY, , Page 255
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ORGANIC CHEMISTRY-II, O, , O, OH +, , C, R, Ester, , BCHCH-202, , OR', , δ–, HO, , C, , O, δ–, OR', , HO, , C, , +, , OR', , R, , R, Transition state, , Fast, O, O, , C, , + R'OH, , R, , 7.9 SUMMARY, In continuation to unit 6 carboxylic acids, this unit make aware the readers about the, most important functional derivatives of carboxylic acids like acyl chlorides (RCOCl),, acid anhydrides ((RCO)2O), esters (RCOOR’ where R and R’ may be same or, different), and amides (RCONH2) which are obtained by the replacement of -OH part of, carboxyl group of acids by –Cl, -OCOR, -OR' or -NH2, groups respectively. This unit, describes the methos of preparation, physical and chemical properties of functional, derivatives of carboxylic acids, viz; a cyl chlorides can be prepared by by heating, carboxylic acids with phosphorous trichloride (PCl3), phosphorus penta chloride (PCl5),, or thionyl chloride (SOCl2),by the reaction of sodium salts of carboxylic acids with, phosphorous trichloride (PCl3) or thionyl chloride (SOCl2). Acid anhydride can be, obtained by the dehydration of carboxylic acids, by heating an acid chloride with a, carboxylate salt,by heating sodium salts of carboxylic acids with acetic anhydride,by, the reaction of excess amount of anhydrous ammonium salts of acid with phosphorus, oxy-chloride or thionyl chloride etc. Esters can be prepared by the interaction of an, alcohol with an acid in presence of a suitable acid catalyst, by the nucleophilic, substitution of acid chlorides or acid anhydrides with alcohols, by the reaction of silver, salt of acids on alkyl halides, by the action of the ethereal solution of diazomethane on, carboxylic acid, by the interaction of an ether with carbon monoxideetc. Similarly, amides are formed by the acylation of ammonia/amines with acyl chlorides, acid, anhydrides or esters,by heating the ammonium salts of carboxylic acids,by the partial, , UTTARAKHAND OPEN UNIVERSITY, , Page 256
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ORGANIC CHEMISTRY-II, , BCHCH-202, , hydrolysis of cyanides with concentrated hydrochloric acid, polyphosphoric acid or, alkaline peroxide.This unit also describes the chemical properties of carboxylic acids, derivatives, like hydrolysis, oxidation, reduction, reactions with hydrazine and its, derivatives, reactions with P2O5, PCl5, NH2OH, diazomethane,ammonia,amines, actin, of heat etc.The uses of function derivatives of carboxylic acids has also been included., , 7.10 TERMINAL QUESTIONS, Section-A, Q.1 Long answered questions, 1. Describe the general methods of preparation, physical and chemical properties of, acyl chlorides., 2. Give the preparation, physical and chemical properties of acid anhydrides., 3. How are acid esters prepared? Describe the important chemical properties of esters., 4. Describe the general methods of preparation, physical and chemical properties of, amides., 5. Describe the mechanism of the acid and alkaline hydrolysis of esters., , Section-B, Q.2 Short answered questions, 1. Explain the followings:, a) Acetyl chloride has lower boiling point than acetic acid., b) Acetyl chloride is more reactive than acetic anhydride., 2. Compare the reactivity of carboxylic acid derivatives towards nucleophilic, substitution., 3. How can you prepare acetyl chloride from carboxylic acids?, 4. How can you prepare esters from silver salts of carboxylic acids?, 5. How can you synthesize amides from cyanides?, 6. Give the mechanism of esterification., 7. How can you convert:, a) Acyl chlorides into esters, , UTTARAKHAND OPEN UNIVERSITY, , Page 257
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ORGANIC CHEMISTRY-II, , BCHCH-202, , b) Esters into amides, c) Amides into amines, d) Amides into carboxylic acids, 8. How will you obtained:, a) Amides from acetyl chloride, b) Tertiary alcohol from acetyl chloride, c) Alcohols from acetic anhydrides, d) Acyl chlorides from esters, , Section-C, Multiple choice questions (MCQ), 1., , 2., , Which functional group is present in a carboxylic acid?, (a) -COOH, , (b) –NO2, , (c) C-O-C, , (d) -SH, , Which one of the followings is an ester?, a) RCOCl, (c) RCOOH, , 3., , (d) RCONH2, , What is the IUPAC name of the given compound?, , (a) o-Benzenedioic anhydride, (c) Ethanoic anhydride, 4., , (b) RCOOR’, , (b) Butanedioic anhydride, (d) Phthalic anhydride, , The given structure is for, , (a) Succinic anhydride, , (b) Diethyl ether, , (c) Acetic anhydride, , (d) Acetone, , UTTARAKHAND OPEN UNIVERSITY, , Page 258
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ORGANIC CHEMISTRY-II, , 5., , BCHCH-202, , Acyl chloride can be obtained, (a) By direct estrification., (b) By the dehydration of acids., (c) From cynohydrin reaction., (d) From carboxylic acids., , 6., , Acyl chlorides are more reactive than other carboxylic acid derivatives, (a) Because their boiling points are higher., (b) Because they are heavier than water., (c) Because they have a pleasant odor., d) Due to electron withdrawing inductive effect of chlorine atom., , 7., , 8., , 9., , 10., , 11., , On reaction with NH3 acid chloride forms, (a) Carboxylic acid, , (b) Amide, , (c) Acid anhydride, , (d) Alcohols, , Esters undergo acid-hydrolysis form, (a) Carboxylic acids, , (b) Acyl chlorides, , (c) Thioethers, , (d) Alcohols, , With LiAlH4 amides reduced to, (a) Acids, , (b) Alcohols, , (c) Primary amines, , (d) None of these, , Anhydrides can be converted into esters with the reaction of, (a) Acids, , (b) Alcohols, , (c) Amines, , (d) Thionyl chloride, , Reduction of acetyl chloride with Pd/BaSO4 will produce, (a) Alcohols, (c) Acid, , 12., , (b) Ketones, (d) Acetaldehyde, , Amide reacts with nitrous acid (HNO2) to form, (a) Acids, , (b) Alcohols, , (c) Amines, , (d) Ketones, , 13. Esters can be prepared by the nucleophilic substitution of, (a) Thiols, , (b) Amides, , (c) Acid anhydrides, , (d) Acid chlorides, , UTTARAKHAND OPEN UNIVERSITY, , Page 259
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 14. Which of the following gives a ketone on reaction with benzene?, (a) Tertiary amine, , (b) Acetyl chloride, , (c) Alcohol, , (d) Esters, , 15. The major product (?) of the reaction is:, , (a) CH3COOC2H5Br, , (b) CH2CHBrCOOC2H5, , (c) CH2BrCOOC2H5, , (d) CH3BrCOOC2H5, , 16., , Esters on reduction with alkali produce, (a) Carboxylic acids, , (b) Primary amines, , (c) Sodium salts of carboxylic acids, , (d) Amides, , Which one of the followings derivatives is most reactive towards nucleophilic, , 17., , substitution, (a) Acyl chloride, , (b) Acid anhydride, , (c) Ester, , (d) Amide, , 18., , Acid amides can be obtained by the, (a) Estrification, , (b) Partial hydrolysis of cyanides, , (c) Reduction of Acetyl chloride, , (d) Hydrolysis of acyl chlorides, , 19., , On reduction with LiAlH4 acetic anhydride produces, (a) Acids, , (b) Amides, , (c) Alcohols, , (d) Ketones, , 20., , On reation with thionyl chloride (SOCl2), esters are converted into, (a) Acid anhydrides, , (b) Alcohols, , (c) Amines, , (d) Acid chlorides, , 7.11 ANSWERS (MCQ):, 26., , (a), , 27., , (b), , 28., , (a), , 29., , (c), , 30., , (d), , 31., , (d), , 32., , (b), , 33., , (a), , 34., , (c), , 35., , (b), , 36., , (d), , 37., , (b), , 38., , (d), , 39., , (b), , 40., , (c), , 41., , (c), , 42., , (a), , 43., , (b), , 44., , (c), , 45., , (d), , UTTARAKHAND OPEN UNIVERSITY, , Page 260
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 7.12 REFERENCES, 1., , Thomas N. and Sorrell Organic Chemistry, IInd edition 2006, Uiversity Sciences, Books, Sausalito, California, , 2., , B.S. Bahal, A. Bahal. Advanced organic chemistry. S. Chand & Company Ltd., Ram Nagar, New Delhi 1993, , 3., , I.L Finar Organic Chemistry, Vol. 2., 5th edition, ELBS & Longman group Ltd.,, 1974., , 4., , R.T.Morrison and R.N.Boyd Organic Chemistry, 6th edition, Prentice Hall, Private Limited, 1997., , 5., , Clayden,Greeves,Warren and Wothers, Organic Chemistry 2nd edition 2012,, Oxford University Press, , 6., , Jagdamba Singh and L.D.S.Yadav, Organic Chemistry vol. I, 8th edition-2013, Pragati Prakashan Pub., , 7., , F.A.Carey and R.J.Sundberg Advanced Organic Chemistry, Plenum Pub. 5th, Edition, 2007, , 8., , B.S. Bahal, A. Bahal. Advanced Organic Chemistry. S. Chand & Company Ltd., Ram Nagar, New Delhi 1993, , UTTARAKHAND OPEN UNIVERSITY, , Page 261
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT-8 ORGANIC COMPOUNDS CONTAINING, NITROGEN, CONTENTS:, 8.1 Objectives, 8.2 Introduction, 8.3 Structure of nitro-compounds, 8.4 Nomenclature of nitro compounds, 8.5 Nitroarenes, 8.6 Preparation of nitroarenes, 8.7 Physical properties of nitroalkanes, 8.8 Chemical reactions of nitroalkanes, 8.9 Mechanism of nucleophilic substitution in nitroarenes, 8.10 Reduction of nitroarenes in different conditions, 8.11 Picric acid (2, 4, 6- trinitrophenol), 8.12 Physical properties of picric acid, 8.13 Chemical properties of picric acid, 8.14 Summary, 8.15 Terminal questions, 8.16 Answers (MCQ), 8.17 References, , UTTARAKHAND OPEN UNIVERSITY, , Page 262
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 8.1 OBJECTIVES, The main objectives of this unit are: To make the students aware about the organic, compounds containing nitrogen particularly the aliphatic and aromatic nitro compounds,, chemical properties of nitroalkanes, mechanism of nucleophilic substitution in, nitroarenes.To explain the reduction of nitroarenes in different media and to describe the, preparation, chemical properties and uses of picric acid., , 8.2 INTRODUCTION, Nitro-compounds are those organic compounds which contain at least one nitro (-NO2), functional group in the molecule. These compounds are obtained by replacing one or, more hydrogen in the hydrocarbon with nitro (-NO2) group. Nitro-compounds may be, aliphatic or aromatic according to the nitro group attached to an alkyl or aryl group., The organic compounds where nitro group (-NO2) is directly attached to the carbon of, hydrocarbon chain are known as aliphatic nitro compounds e.g. nitromethane (CH3NO2),, nitroethane (C2H5NO2), 1-nitropropane (NO2CH2CH2CH3), whereas the compounds, where nitro group (-NO2) is directly attached to an aromatic ring are known as aromatic, nitro compounds or nitroarenes such as nitrobenzene (C6H5NO2), m-dinitrobenzene, 2nitroethylbenzene, p-nitrotoluene, o-nitroaniline, 2,4,6-trinitrophenol etc. The aliphatic, nitro compounds may be further classified into primary, secondary or tertiary nitro, compounds as the nitro group is attached to primary, secondary or tertiary carbon atom, respectively., , Nitro compounds are found naturally in plants and animals, and can be synthesized., These compounds are associated in many hormones, vitamins, and amino acids and, proteins. These compounds possess wide chemical reactivity and used in the synthesis of, several important products like drugs, agrochemicals, polymers (nylon), dyes and, , UTTARAKHAND OPEN UNIVERSITY, , Page 263
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ORGANIC CHEMISTRY-II, , BCHCH-202, , explosives. There are many functional groups, which contain one or more nitrogen atoms, includes nitro compounds, amines, cyanides, isocyanides, diazo compounds etc., , 8.3 STRUCTURE OF NITRO COMPOUNDS, The nitro group is an ambident group and is capable of getting attached to carbon chain, through nitrogen as well as through oxygen (-O-N = O) atom., , The compound in which the -NO2 group is linked to the alkyl or aryl group through, oxygen atom are called nitrites. Nitrites are isomeric with nitro compounds. These, compounds are also known as alkyl esters of nitrous acid The general formula of an alkyl, nitrile is as:, , O, CH3, , O, , N O, , N O, , The nitrogen is trigonal planar with a bond angles of 120°, there are two resonance forms, so implying that the two oxygen’s are equivalent., , O, N, O, , UTTARAKHAND OPEN UNIVERSITY, , O, CH3, , N, , O, , Page 264
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 8.6 PREPARATION OF NITROARENES, Nitroarenes can be prepared by the following general methods:, , 1. By the nitration of aromatics: The aromatic nitro compounds can be prepared by the, direct nitration of aromatics. The formation of nitroarene depends upon the temperature,, nature of the nitrated aromatic compound and nature of reagent used. For example,, nitrobenzene is prepared by the direct nitration of benzene using concentrated HNO3 and, H2SO4 at about 30-40ºC., , The nitrophenol is prepared by the nitration of phenol in presence of HNO3 and H2O at, 20ºC., , Nitrotoluene can be prepared by the nitration of toluene with concentrated HNO3 and, H2SO4 at about 20-30ºC., , UTTARAKHAND OPEN UNIVERSITY, , Page 268
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. By the oxidation of amino group to nitro group: p-dinitrobenzene can be prepared, by the oxidation of amino group into nitro group with per-acids such as persulphuric acid, (H2S2O8) and peroxy trifluoroacetic acod (CF3CO3H)., , 3. By the replacement of amino group by nitro group: The –NH2 group in aromatic, group can bereplaced by treating the compound with NaNO2/HBF4 as follow, , 8.7 PHYSICAL PROPERTIES OF NITROALKANES, The nitroalkanesposses following physical properties, 1. Most nitro compounds are yellow crystalline solids; few are pale yellow liquids (e.g., nitrobenzene) with strong characteristic odor, whereas nitro-alkanes are colorless, oily liquids with pleasant smell., 2. Nitro compounds are insoluble in water but soluble in organic solvents., 3. The density of nitro compounds is greater than 1, therefore they are heavier than, water., 4. Nitro compounds have high boiling points than their corresponding hydrocarbons, due to high polarity. Their melting and boiling points increase with the number of, nitro groups present. For example, the boiling point of nitrobenzene is 211ºC, whereas the boiling point of m-dinitrobenzene is 303ºC., , UTTARAKHAND OPEN UNIVERSITY, , Page 269
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 5. Aromatic nitro compounds are used as a solvent in many inorganic reactions., 6. Aromatic nitro compounds such as 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene, (TNB), Research and development explosive (RDX) are highly toxic and used as, explosives., , 8.8 CHEMICAL PROPERTIES OF NITROALKANES, , O, CH3, , N, , O, Nitroalkanes are nitro derivatives of alkanes obtained by the replacement of a hydrogen, atom by a nitro group. They are isomeric with alkyl nitriles. Nitroalkanes are named by, prefixing ‘nitro’ to the name of the parent hydrocarbon e.g., C2H5NO2 (nitroethane),, C3H7NO2 (nitropropane) etc., Nitroalkanes may be primary, secondary or tertiary according the nitro group attached to, a primary, secondary and tertiary carbon. They are colorless liquids having pleasant, odor. Nitromethane is sparingly soluble in water while higher nitroalkanes are insoluble, in water but soluble in organic solvents. They have high boiling points. They are highly, polar organic compounds., , 1. Acidic character: The nitroalkanes are containing α-hydrogen atoms exhibit acidic, character due to electron withdrawing nature of nitro group., , Nitroalkanes containing α-hydrogen react with a strong alkali to form salts., , UTTARAKHAND OPEN UNIVERSITY, , Page 270
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. Reduction: Nitro compounds can be reduced to primary amines under a variety of, conditions. Various reduction stages of the nitro group are given below: The final, product depends upon the pH of the reaction medium and nature of the reducing agent., , (i) Reduction in acidic medium: Nitroalkanes can be reduced to the corresponding, primary amines by a combination of active metals (Zn, Fe or Sn) and concentrated, hydrochloric acid (HCl)., , CH3CH2CH2NO2, , Fe/HCl, , CH3CH2CH2NH2, , (ii) Reduction in neutral medium: Reduction with zinc dust and ammonium chloride, solution in neutral medium, nitroalkanes are converted into corresponding Nalkyl hydroxyl amines., , Nitromethane on reduction with zinc dust and ammonium chloride solution in neutral, medium converted into N-methylhydroxy amine., , (iii) Catalytic reduction: The nitro group of an aliphatic and aromatic nitro compound, is easily reduced to corresponding primary amines with hydrogen using raney Ni, Pt or, Pd catalyst., , UTTARAKHAND OPEN UNIVERSITY, , Page 271
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ORGANIC CHEMISTRY-II, , BCHCH-202, , aromatic nitro compounds like nitrobenzene, m-dinitrobenzene etc., and tertiary nitro, compounds do not show tautomerism due to the absence of α-hydrogen atom on αcarbon atom., , 5. Halogenation: Primary and secondary nitroalkanes on treatment with halogen, (chlorine or bromine) in presence of alkali form halonitroalkanes. During this reaction,, all three hydrogen atoms of nitroalkanes are replaced by the halogen atoms., , 6. Reaction with aldehydes: Nitroalkanes having α-hydrogen can undergo nucleophilic, addition reaction with aldehydes similar to aldol type addition reaction., , UTTARAKHAND OPEN UNIVERSITY, , Page 273
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 7. Action with nitrous acid: Nitroalkanes on reaction with nitrous acid give different, products depending upon the type of nitro compound., Primary nitroalkanes on reaction with nitrous acid give nitrolic acids which dissolve in, alkalies to form a red solution., , Whereas, secondary nitroalkanes on reaction with nitrous acid give blue colored pseudonitroles which do not dissolve in alkali., , Tertiary nitroalkanes do not react with nitrous acid since they do not have α-hydrogen, atom., , Uses of nitro compounds: Nitroalkanes e.g. nitromethane, nitroethane etc. and, nitrobenzene are extensively used as solvent in industry., 1. Nitroarenes are important intermediates in the manufacture of polymers detergents,, dyes and pharmaceuticals., , UTTARAKHAND OPEN UNIVERSITY, , Page 274
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. Addition elimination mechanism of nitrochlorobenzene: The nitro substituted aryl, halides undergo reaction with nucleophiles such as ammonia and hydroxide, where the, chlorine is eliminated/substituted e.g. p-chloronitrobenzene reacts with sodium, methoxide at 85 ºC to form the p-nitroanisole., , The mechanism of the formation of p- nitroanisole from p-chloronitrobenzene is as, follows:, , UTTARAKHAND OPEN UNIVERSITY, , Page 276
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 8.10 REDUCTION OF NITROARENES IN DIFFERENT, CONDITIONS, The nitroarenes give different products while reduced in different reaction conditions, such as nature of reducing agents and the pH of the reaction medium as follow, , (i) Reduction of nitroarenes in acidic medium: Nitroarenes can be easily reduced to, corresponding primary aryl amines by tin metal and hydrochloric acid. For example, the, reduction of nitrobenzene with tin metal and hydrochloric acid gives aniline., , Mechanism:, , UTTARAKHAND OPEN UNIVERSITY, , Page 277
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 1. The reduction of nitrobenzene to aniline is an example of oxidation reduction reaction, in which the Sn0 is oxidized to stannic ion Sn4+ by the donation of four electrons to, substrate to form an intermediate., 2. This intermediate radical is then ion protonated, the protons are provided by the acid., 3. The oxygen atom from the nitro group is removed as water molecule. The scheme of, this reaction mechanism is as:, O, C6H5, , N, , +e, , Sn, , O, C6H5, , H+, , N, , O, , C6H5, , OH, N, + e, , O, , O, , H+, OH, C6H5, , O, , N, , C6H5, O, , C6H5, , C6H5, , +e, , N, , N, , H+, , O, H, , OH, N, + e, , C6H5, , C6H5, , NH3, , N, , OH, , NaOH, , H+, , C6H5, , C6H5, , N, , OH, , Sn, 3H+, , NH2, , (ii) Reduction of nitroarenes in neutral medium: With iron and steam a nitro, compound gets reduced to nitroso compounds., , The reduction of nitrobenzene with zinc metal and ammonium chloride or calcium, chloride gives only N-phenylhydroxylamine. The hydroxylamines are reducing agents, and can reduce Tollen’s reagent., , UTTARAKHAND OPEN UNIVERSITY, , Page 278
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ORGANIC CHEMISTRY-II, NO2, , BCHCH-202, NHOH, , + 2Zn + 4NH4Cl, Nitrobenzene, , + 2ZnCl2 + 4NH3 + H2O, Phenylhydroxylamine, , (iii) Reduction of nitroarenes in alkaline medium: Whilst acidic and neutral reduction, result in the formation of mono-nuclear compounds, reaction in alkaline medium yields a, variety of binuclear compounds due to the interaction of nitroso- and hydroxylamine, derivatives formed during the reduction. The reduction of nitrobenzene yields different, products depending upon the nature of reducing agent used. The scheme of alkaline, reduction is given below:, , (i) The product-I, azoxybenzene is formed by the reduction of nitrobenzene with alkaline, sodium arsenite (Na3AsO3/NaOH)., (ii) The product-II, azobenzene is formed, when nitrobenzene is reduced with zinc dust, and methanolic caustic soda solution, or by alkaline stannite., (iii) The product-III, hydrazobenzene is obtained by reduction of nitrobenzene with zinc, dust and aqueous sodium hydroxide (Zn/NaOH)., , UTTARAKHAND OPEN UNIVERSITY, , Page 279
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (iv) Electrolytic reduction: Electrolytic reduction of nitrobenzene in weakly acidic, medium gives aniline but in strongly acidic medium, it gives p-aminophenol obviously, through the acid catalyzed rearrangement of initially formed phenyl hydroxyl amine., NO2, , NH2, Electrolytic reduction, Weak acidic medium, , Nitrobenzene, , Aniline, , (v) Selective reduction: If two or more nitro groups are present in the benzene ring, it is, possible to reduce one of them without affecting the others. Such reductions are called, selective reductions. For example, reduction of m-dinitrobenzene with sodium or, ammonium sulphide gives m-nitroaniline. This reduction of nitro compounds with, sulphides and polysulphides is called Zinin reduction., , (vi) Catalytic reduction: Nitrobenzene is reduced to aniline with hydrogen using Pt or, Ni catalyst., , UTTARAKHAND OPEN UNIVERSITY, , Page 280
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ORGANIC CHEMISTRY, CHEMISTRY-II, , BCHCH, BCHCH-202, , 2. From chlorobenzene: Picric acid can be obtained by the reaction oof nitric acid, followed by hydrolysis and followed by nitration., , 3. From trinitro benzene: Picric acid can be prepared by the oxidation of symsym, trinitrobenzene with potassium ferricyanide., OH, O 2N, , O 2N, , NO, O2, , N 2, NO, , [O], K 3Fe(CN)6, NO 2, , NO 2, , Trinitrobenzenee, , Picric acid, , 8.12 PHYSICAL PROPERTIES OF PICRIC ACID, Picric acid is a yellow crystalline solid and one of the most acidic phenols. It is volatile,, flammable, highly toxic and bitter in taste. Its melting point is 122ºC. It is sparingly, soluble in water, but soluble in hot water, alcohols and ethers., ethers. It is explosive when dry, , and forms picrates when exposed with metals. Picric acid is especially hazardous, because it is volatile and slowly sublimes even at room temperature., , 8.13 CHEMICAL PROPERTIES OF PICRIC ACID:, 1. Picric acid is much stronger acidic, acid than phenol due to –NO2 functional group. Picric, acid reacts with NaHCO3 to liberate CO2., , UTTARAKHAND OPEN UNIVERSITY, , Page 282
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. Picric acid on reaction with phosphorus pentachloride forms picryl chloride., , 3. On reduction with sodium sulphide (Na2S) in presence of water, picric acid gives, picramic acid., , Uses: Picric acid is used in electric batteries, leather industry, dyes, pigments, inks,, paints, manufacture of colored glass, textile mordents, as a laboratory reagent, in, matches and explosives., , UTTARAKHAND OPEN UNIVERSITY, , Page 283
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 8.14 SUMMARY, This unit reveals the knowledge of organic compounds in which nitrogen is covalently, attachedwith carbon like alkyl or aryl groups. Emphasis has been given particularly to, aware the readers about organic compounds which contain at least one nitro functional, group in the molecule generally known as nitro-compounds. These compounds may be, aliphatic or aromatic according to the nitro group attached to alkyl or aryl group., Aromatic nitro compounds, also called nitroarenes, having –NO2 group on o, m or p, position of a benzene ring e.g. nitrobenzene, o-nitrotoluene, p-nitrotoluene, 4nitrophenol, 2,6- dinitrotoluene, 2,4,6-trinitrotoluene, 1,3,5-trinitrobenzene etc.These, compounds can be prepared by the direct nitration of aromatic compounds, by the, oxidation of amino group to nitro, by the replacement of amino group by nitro etc.The, aliphatic nitro compounds can be primary, secondary or tertiary types depending upon, the nature of carbon with which –NO2 group is attached.The primary and secondary, aliphatic nitro compounds α-hydrogen containing are acidic due to electron withdrawing, nature of nitro group. The nitro compounds are easily reduced with various reducing, agents in different mediums. The final product formed depends on the nature of reducing, agent and the pH of the medium.This unit also describes the individual nitro compound, picric acid (2, 4, 6-trinitrophenol) which can be obtained by the sulphonation of phenol, followed by the nitration, by the reaction of nitric acid followed by hydrolysis and, followed by nitration, by the oxidation of trinitrobenzene with potassium ferricyanide., The physical, chemical properties alongwith the uses of picric acid has also been, described in this unit., , 8.15 TERMINAL QUESTIONS, , Section-A, Long answered questions, 1.What are nitro compounds? Describe the nomenclature and general methods of, preparation of nitroarenes., 2. Describe the chemical properties of nitroalkanes., , UTTARAKHAND OPEN UNIVERSITY, , Page 284
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 3.How can you prepare nitroarenes from: (i) the nitration of aromatics (ii) from pnitrobenzene (iii) from p-nitroaniline?, 4. Describe the mechanism of, a) Nucleophilic aromatic substitution in nitroarenes., b) Reduction of nitrobenzene in acidic medium., 5. Describe the general methods of preparation, chemical properties and uses of picric, acid., , Section-B, Short answered questions, 1., , What are nitro compounds? Explain the structure of nitro compounds., , 2., , How can you distinguish between alkyl and aryl nitro compounds?, , 3., , Write a short note on nitroarenes., , 4., , Write the physical properties of nitro compounds., , 5., , Describe the reduction of nitrobenzene in acidic, neutral and alkaline medium., , 6., , Give the mechanism of nucleophilic substitution in nitroarenes., , 7., , Explain the followings:, , (a), , Acidic character of nitroalkanes, , (b), , Halogenation of nitroalkanes, , 8., , How can you convert?, , (a), , Primary nitroalkanes into carboxylic acids, , (b), , Secondary nitroalkanes into ketones, , (c), , Nitroalkane into primary amine, , (d), , Nitromethane to chloropicrin, , 9., , How will you obtained:, , (a), , Nitrobenzene from benzene, , (b), , p-Nitronitrosobenzene from p-dinitrobenzene, , (c), , Picric acid from chlorobenzene, , (d), , Picramide from picric acid, , UTTARAKHAND OPEN UNIVERSITY, , Page 285
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ORGANIC CHEMISTRY-II, 6., , BCHCH-202, , Nitroarenes can be obtained, (a) By heating haloalkanes with potassium sulphide., (b) By the oxidation of alcohols with KMnO4., (c) By heating alkyl halide with alcoholic AgNO2., d) By the nitration of benzene., , 7., , Nitroalkanes are more acidic than corresponding hydrocarbons, (a) Because their boiling points are higher., (b) Because they are heavier than water., (c) Because they have a pleasant odor., (d) Due to the electron withdrawing nature of nitro group., , 8., , 9., , 10., , The reduction nitroalkanes with Fe and concentrated HCl give, (a) Hydroazobenzene, , (b) Primary amines, , (c) Hydroxylamine, , (d) Azobenzene, , Secondary nitroalkanes undergo hydrolysis with boiling HCl give, (a) Ketones, , (b) Carboxylic acids, , (c) Thioethers, , (d) Alcohols, , Reduction in which the nitroalkanes are reduced to corresponding N-alkyl, hydroxyl amines with zinc dust and ammonium chloride solution is conducted in, , 11., , (a) Acidic medium, , (b) Alkaline medium, , (c) Neutral medium, , (d) None of these, , Nitrobenzene is converted into azobenzene by reduction with, (a) Alkaline sodium stannite, (b) Alkaline sodium arsenite, (c) Zinc and ammonium chloride, (d Zinc metal and aqueous sodium hydroxide, , 12., , Reduction of nitrobenzene with LiAlH4 will produce, (a) Azoxybenzene, (c) m-Dinitrobenzene, , 13., , 14., , (b) p-Aminophenol, (d) Aniline, , Nitroethane reacts with nitrous acid (HNO2) to form, (a) Nitrolic acid, , (b) Nitrous oxide, , (c) Hydroxylamine, , (d) Ethanamide, , Tertiary nitroalkanes cannot tautomerise because they, , UTTARAKHAND OPEN UNIVERSITY, , Page 287
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (a) Are stable, , (b) Are not stable, (d) Do not contain α-hydrogen, , (c) Are saturated hydrocarbons, 15., , 16., , Which of the following gives a ketone when boiled with concentrated HCl?, (a) Primary nitroalkanes, , (b) Secondary nitroalkanes, , (c) Tertiary nitroalkanes, , (d) All of the above, , The major product (X) of the reaction is:, , (b) HO, , NH NH, , (a), , hydrazobenzene, , NH2, , p _ aminophenol, O, , (c), , N N, , (d), , azobenzene, 17., , 18., , 19., , 20., , 21., , N N, azoxybenzene, , Nitromethane on reduction with Zn and NH4Cl gives:, (a) Methanamide, , (b) Ethylamine, , (c) N-Methylhydroxy amine, , (d) Methylamine, , Which compound is obtained at the end of the following reaction?, , (a) Acetic acid, , (b) Formaldehyde, , (c) Methanethiol, , (d) Methyl chloride, , Chloropicrin is formed by the halogenation of nitromethane with, (a) Bromine, , (b) Chlorobenzene, , (c) Chlorine, , (d) Toluene, , The reduction of nitrobenzene with zinc and sodium hydroxide gives, (a) Azobenzene, , (b) Azoxybenzene, , (c) Nitrosobenzene, , (d) Hydrazobenzene, , Picric acid can be obtained from, , UTTARAKHAND OPEN UNIVERSITY, , Page 288
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (a) Hydrolysis of picryl chloride, (b) Phenol by sulphonation followed by the nitration, (c) Nitration of benzoic acid, (d) Nitration of toluene, 22., , 23., , On reduction with NaHCO3, picric acid gives, (a) Picramide, , (b) m-Dinitrobenzene, , (c) Sodium picrate, , (d) Picramic acid, , The reduction of picric acid with sodium sulphide (Na2S) in presence of water, gives, (a) Picramic acid, , (b) Picramide, , (c) Sodium picrate, 24., , (d) Trichlorobenzene, , The reduction of nitrobenzene with Sn and HCl gives, (a) Azoxybenzene, , (b) Hydroazobenzene, (d) p-Aminophenol, , (c) Primary aryl amines, 25., , Primary nitroalkanes are upon hydrolysis with concentrated hydrochloric acid, gives, (a) Primary amines, , (b) Ketones, , (c) Alcohols, , (d) Carboxylic acids, , 8. 16 ANSWER (MCQs), 1., , (b), , 2., , (c), , 3., , (a), , 4., , (b), , 5., , (c), , 6., , (d), , 7., , (d), , 8., , (b), , 9., , (a), , 10., , (c), , 11., , (a), , 12., , (d), , 13., , (a), , 14., , (d), , 15., , (b), , 16., , (a), , 17., , (c), , 18., , (a), , 19., , (c), , 20., , (d), , 21., , (b), , 22., , (c), , 23., , (a), , 24., , (c), , 25., , (d), , 8. 17 REFERENCES, Douglas E. Rickert, Toxicity of Nitroaromatic Compounds, Chemical Industry, Institute of Toxicology Series, CRC Press, Washington, 1985., , UTTARAKHAND OPEN UNIVERSITY, , Page 289
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Tokiwa H, Ohnishi Y., Mutagenicity and carcinogenicity of nitroarenes and their, sources in the environment. Crit Rev Toxicol. 1986; 17(1): 23-60., , K. S. Tewari, N. K. Vishnoi and S. N. Mehrotra, A Text Book of Organic Chemistry,, 2nd Revised Edition, Vikas Publishing House Pvt Ltd, New Delhi, 2003., , National Toxicology Program (NTP) (NIH), Report on Carcinogens (12th Ed.),, DIANE Publishing, India, 2011., , Paul C. Howard, Stephen S. Hecht, Frederick A. Beland, Nitroarenes: Occurrence,, Metabolism, and Biological Impact, Volume 40 of Environmental Science Research,, Springer Science & Business Media, New York, 2012., , Mehta, Bhupinder, Mehta, Manju, Organic Chemistry, 2nd Edition, PHI Learning Pvt., Ltd., Delhi, 2015., , B.S Bahal, Arun Bahal, Advanced organic chemistry, 1993, S. Chand & Company, Ltd. New Delhi., , UTTARAKHAND OPEN UNIVERSITY, , Page 290
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT-9 AMINO COMPOUNDS, CONTENTS:, 9.1 Objectives, 9.2 Introduction, 9.3 Structure of amino caompounds, 9.4 IUPAC nomenclature of aliphatic amines, 9.5 IUPAC nomenclature of aromatic amines, 9.6 Physical properties of amines, 9.7 Stereochemistry of amines, 9.8 Separation of a mixture of primary, secondary and tertiary amines, 9.9 Structural features effecting basicity of amines, 9.10 Preparation of alkyl and aryl amines, 9.11 Reductive amination of aldehydic and ketonic compounds, 9.12 Important reactions of amines, 9.13 Summary, 9.14 Terminal questions, 9.15 Answers (MCQ), 9.16 References, , UTTARAKHAND OPEN UNIVERSITY, , Page 291
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.1 OBJECTIVES, In continuation to unit 8 (organic compounds containing nitrogen) the aim of this unit is, to describe amines as derivatives of ammonia having a pyramidal structure, classify, them as primary, secondary and tertiary amines,describe their common and IUPAC, names. To explain that how we can distinguish between primary, secondary and tertiary, amines? To describe some of the important methods of preparation of amines, to, explain their physical and chemical properties and to study the mechanism of the, reductive amination of aldehydes and ketonic compounds, Gabriel’s phthalimide, synthesis and Hofmann’s bromamide reaction etc., , 9.2 INTRODUCTION, Amines are aliphatic and aromatic derivatives of ammonia which are obtained by the, replacement of one, two or all three hydrogen atoms of ammonia by alkyl or aryl, groups. Amines are described as primary (1o), secondary (2o) or tertiary (3o) depending, on how many alkyl or aryl substituents are attached to the nitrogen atom. The tetra alkyl, derivatives of ammonium salts are known as quaternary ammonium salts e.g.,, tetramethyl ammonium chloride, (CH3)4N+Cl-., , R, , R, , N, H, Secondary amine, , R, N, R, Tertiary amine, , H, R, N, H, Primary amine, , R, , Primary amines: Primary amines are obtained by the replacement of one hydrogen, atom of ammonia by an alkyl or aryl group. For example: Methyl amine, ethyl amine,, phenyl amine etc., , CH3NH2, , CH3CH2NH2, , methylamine, , ethylamine, , UTTARAKHAND OPEN UNIVERSITY, , CH2NH2, benzylamine, , Page 292
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.3 STRUCTURE OF AMINO COMPOUNDS, Amines are ammonia derivatives; the shape of amine functional group is similar to its, parent molecule ammonia. The nitrogen in ammonia forms three σ bonds and also, carries one lone pair of electrons. The nitrogen in ammonia as well as aliphatic amines, is sp3 hybridized. Therefore the shape of ammonia is trigonal pyramidal which can be, represented as, , The amino compounds are obtained by replacing hydrogen atom by alkyl or aryl, groups, their shape can be represented as:, , The bond angle between H-N-H in ammonia is 107º, the bond angle in amine is, , assumed almost same as in ammonia., , 9.4 IUPAC NOMENCLATURE OF ALIPHATIC AMINES, Usually amines are named after the alkyl group attached to the nitrogen atom., In IUPAC nomenclature, the primary amines are named as aminoalkanes; secondary, amines are named as N-alkylaminoalkanes and tertiary as dialkylaminoalkanes., , Compound, , Common name, , IUPAC name, , CH3NH2, , methyl amine, , aminomethane, , CH3CH2NH2, , ethyl amine, , aminoethane, , CH3CH2CH2NH2, , propyl amine, , aminopropane, , Primary amines, , UTTARAKHAND OPEN UNIVERSITY, , Page 294
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ORGANIC CHEMISTRY-II, , BCHCH-202, , isopropyl amine, , 2-methylaminoethane, , CH3NHCH3, , dimethyl amine, , N-methylaminomethane, , CH3NHC2H5, , ethyl methyl amine, , n-methylaminoethane, , CH3NHC3H7, , methyl propyl amine, , N-methylaminopropane, , trimethyl amine, , N,N-dimethylaminomethane, , diethyl methyl amine, , N-ethyl-N-methyl, , Secondary amines, , Tertiary amines, , aminoethane, , 9.5: IUPAC NOMENCLATURE OF AROMATIC AMINES:, The simplest member of aromatic amines is aminobenzene (aniline). Amines containing, a –NH2 group, firstly identified the position of the amino group and count this position, as position-1 of the ring., , Then give numbers to all positions (as 2, 3, 4, 5, 6 etc.) in, , clockwise direction. They are named as o, m or p substituted. The next position to the, amino group is ortho (o), the third position to the amino group is meta (m) and the, vertically opposite position to the amino group is para (p)., , UTTARAKHAND OPEN UNIVERSITY, , Page 295
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ORGANIC CHEMISTRY-II, , BCHCH-202, , diphenyl amine, , N-phenyl amine, , 9.6 PHYSICAL PROPERTIES OF AMINES, 1. Physical state: Lower amines are combustible gases at room temperature, C3-C11, members of amines are volatile liquids, while the higher amines are solids. The lower, members of amines have fishi ammoniacal odour,, , 2. Hydrogen bonding: Amines are polar compounds and both primary and secondary, amines form intermolecular hydrogen bonds. The boiling points and solubility of, amines are associated with the intermolecular hydrogen bonding involved in these, molecules., , hydrogen bonding, δ+, H δ−, N, R, R, , R, δ+ δ− R, H N, , 3. Boling points: An N-H---N hydrogen bond is weaker than O-H---O hydrogen bond, because the electronegativity difference between nitrogen and hydrogen (0.9) is less, than between oxygen and hydrogen (1.4). Therefore amines have lower boiling points, than the corresponding alcohols. Tertiary amines cannot form hydrogen bond because, they have no hydrogen therefore the boiling point of tertiary amines will be even lower, than primary or secondary amines., , 4. Solubility of amines: Primary and secondary amines form hydrogen bonds with, water and are more soluble in water than hydrocarbons of comparable molecular, weight. Low molecular weight amines are completely soluble in water while higher, molecular weight amines are moderately soluble or insoluble in water., , UTTARAKHAND OPEN UNIVERSITY, , Page 297
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.7 STEREOCHEMISTRY OF AMINES, Amines are classified into primary, secondary and tertiary based on the number of, hydrogen atom (s) are replaced by the alkyl or aryl groups. Tertiary amines have three, different groups i.e. R1, R2, and R3 attached to the nitrogen atom, they are asymmetric, or chiral, and therefore they do not form superimposable mirror image. Tertiary amines, exist in two enantiomeric forms. This is due to the inability of unshared pair of, electrons present in fourth sp3 orbital of nitrogen to serves as a fourth group to keep, configuration., , In contrast, quaternary ammonium salts, in which the nitrogen atom is attached to four, different groups. In quaternary ammonium salts, the groups may also be chiral and able, to show enatiomerism as well as optical activity. This is because the nitrogen in these, salts is tetrahedral and all its sp3 orbitals are involved in the bond formation., Amines display different characteristic infrared absorption peaks based on the degree of, amines., a) Primary amines contain two N-H bonds which display two peaks around 3300 cm-1, The shape of IR peak is similar to the molar teeth, hence also known as “ molar, peak”, b) Secondary amines contain one N-H bond which displays a single peak around 3300, cm-1, c) Tertiary amines contain no N-H bonds and do not show up in infrared spectroscopy., , 9.8, , SEPARATION, , OF, , A, , MIXTURE, , OF, , PRIMARY,, , SECONDARY AND TERTIARY AMINES, There are two methods which are used to distinguished the primary, secondary and, tertiary amines i.e. Hinsberg,s method and Hofmann's method., , UTTARAKHAND OPEN UNIVERSITY, , Page 298
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. Hofmann's method: The mixture of three amines is treated with diethyl oxalate. The, primary amine forms a solid oxamide; a secondary amine gives a liquid oxamic ester, while tertiary amine does not react., , Now, the mixture containing primary, secondary and tertiary amines is subjected to, fractional distillation, when tertiary amine, which is highly volatile, distils over. The, remaining residue mixture containing solid oxamide and liquid oxamic ester are, separated by the simple filtration. Both solid oxamide and liquid oxamic ester are, separately treated with a strong alkali like KOH to recover and purified by the, distillation., , UTTARAKHAND OPEN UNIVERSITY, , Page 300
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.9 STRUCTURAL FEATURES EFFECTING BASICITY OF, AMINES, Amines, like ammonia are weak bases (Kb = 10-4 to 10-6). The basicity of amines is due, to the presence of unshared pair of electrons on nitrogen atom which can share with, other atoms. This unshared pair of electrons creates an electron density around the, nitrogen atom. The greater the electron density, the more basic is the amine. Electron, releasing groups (e.g., methyl, ethyl, and other alkyl groups) increase the basicity of, aromatic amines whereas electron withdrawing groups (e.g., halogen, nitro, carbonyl, groups) decrease the basicity of aromatic amines. Thus, the basicity of aliphatic amines, increases with increases alkyl substitutions as given below:, CH3, CH3, , N, , CH3, , NH, , CH3NH2, , NH3, , CH3, , CH3, , However, in aqueous solutions, the order of basicity changes., CH3, CH3NH2, , CH3, , NH, , CH3, , N, , NH3, , CH3, , CH3, The differences in the basicity order in the gas phase and aqueous solutions are the, , result of solvation effects. Amines in water solution exist as ammonium ions., , In water, the ammonium salts of primary and secondary amines undergo solvation, effects (due to hydrogen bonding) to a much greater degree than ammonium salts of, , UTTARAKHAND OPEN UNIVERSITY, , Page 301
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ORGANIC CHEMISTRY-II, , BCHCH-202, , tertiary amines. These solvation effects increase the electron density on the amine, nitrogen to a greater degree than the inductive effect of alkyl groups., Amines act as nucleophiles in most circumtances; the unshared pair of electrons on, nitrogen forms a new covalent bond with hydrogen and displaces hydroxide ion., , The equilibrium constant for this reaction is as follows:, , The base ionization constant Kb = Keq [H2O]. The value of Kb for methylamine is 4.37 x, 10-4 (pKb = 3.36)., , Amines are basic in nature (Lewis base) the basic strength in term of their pKb values, are being given in table 1. The smaller the pKb value stronger is the base., , Table -1: Basic strength of amines (pKb):, Compound, , Structure, , pKb, , ammonia, , NH3, , 4.74, , methylamine, , CH3NH2, , 3.36, , ethylamine, , CH3CH2NH2, , 3.34, , Primary amines, , UTTARAKHAND OPEN UNIVERSITY, , Page 302
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ORGANIC CHEMISTRY-II, pyridine, , piperidine, , BCHCH-202, ~8.7, , 2.7, , All aliphatic amines have about the same base strength, pKb 3.0 - 4.0 and are slightly, stronger bases than ammonia. The increase in basicity compared with ammonia can be, attributed to the greater stability of an alkyl ammonium ion, as for example, RCH2NH3+,, compared with the ammonium ion, NH4+. This greater stability arises from the electron, releasing effect of alkyl groups and the resulting partial delocalization of the positive, charge from nitrogen onto carbon in the alkyl ammonium ion., Aromatic amines are weaker bases than ammonia and aliphatic amine. The less basic, character of anilines can be explained on the following bases:, , 1. Delocalization of the unshared electron pair on nitrogen atom: The resonance, stabilization of the free base form of aromatic amines. For aniline and other aryl, amines, this resonance stabilization is a result of interaction of the unshared pair on, nitrogen with the π- system of the aromatic ring. Due to this interaction the electron pair, on nitrogen is less available for reaction with acid. No such resonance stabilization is, possible for alkyl amines and therefore the electron pair on the nitrogen of an alkyl, amine is more available for reaction with acid; alkyl amines are stronger bases than aryl, amines., , UTTARAKHAND OPEN UNIVERSITY, , Page 304
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 2. Substituent effect: The second factor contributing to the decreased basicity of, aromatic amines is the electron withdrawing effect of the sp2-hybridized carbons of the, aromatic ring compared with the sp3-hybridized carbons of aliphatic amines. The, unshared pair of electrons on nitrogen in an aromatic amine is pulled toward the ring, and, therefore, less available for protonation to form the conjugate acid of the amine., , Electron releasing groups (e.g., methyl, ethyl, and other alkyl groups) increase the, basicity of aromatic amines whereas electron withdrawing groups (e.g., halogen, nitro,, carbonyl groups) decrease the basicity of aromatic amines., The decrease in basicity on halogen substitution is due to the electron withdrawing, inductive effect of the electronegative halogen. The decrease in basicity on nitro, substitution is due to a combination of inductive and resonance effects, as can be seen, by comparing the base ionization constants of 3-nitroaniline (pKb 11.53) and 4nitroaniline (pKb 13.0). Note that the conjugate acid of 4-nitroaniline (pKa 1.0) is a, stronger acid than phosphorous acid (pKa 2.0). Heterocyclic aromatic amines are, weaker bases than aliphatic amines. When a nitrogen atom is incorporated directly into, an aromatic ring, its basicity depends on the bonding context. For example, In pyridine, ring, the nitrogen lone pair occupies an sp2 orbital which is not a part of the aromatic, sextet., , Proton transfer from water or other acid to pyridine does not involve the electrons of the, aromatic sextet. Pyridine is a weaker base than aliphatic amines because the unshared, pair of electrons of the pyridine nitrogen lies in sp2 hybrid orbital, whereas in aliphatic, amine, the unshared pair lies in sp3 orbital. Electrons in sp2 hybrid orbital (33% s, character) are held more tightly by the nucleus than electrons in sp3 hybrid orbital (25%, , UTTARAKHAND OPEN UNIVERSITY, , Page 305
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ORGANIC CHEMISTRY-II, , BCHCH-202, , s character). It is this effect that decreases the basicity of the electron pair on sp2, hybridized nitrogen compared with that on sp3 hybridized nitrogen., , There are two nitrogen atoms in imidazole, each with an unshared pair of electrons. One, shared pair lies in a 2p orbital and is an integral part of the (4n+2) pi electrons of the, aromatic system. The other unshared pair lies in an sp2 hybrid orbital and is not part of, the aromatic sextet. It is the pair of electrons not part of the pi system that functions as, the proton acceptor., In pyridine the unshared pair of electrons functioning as the proton acceptor and in, imidazole lies in sp2 hybrid orbital and has decreased basicity compared with an, unshared pair of electron in sp3 hybrid orbital. The positive charge on the imidazolium, ion is delocalized on both nitrogen atoms of the ring and, therefore, imidazole is a, stronger base than pyridine., , 9.10 PREPARATION OF ALKYL AND ARYL AMINES, The alkylation of ammonia, Gabriel’s phthalimide synthesis, Hofmann’s bromamide, synthesis, reduction of nitriles, reduction of oximes and acid amides, reduction of, nitroarenes, and reductive amination of aldehydes and ketones are methods commonly, used for preparing amines., , A. Methods for the preparation of all three types of amine along with quaternary, ammonium salts., , UTTARAKHAND OPEN UNIVERSITY, , Page 306
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 3. From carbonyl compounds: On heating with an acidic solution of ammonia or, amine, carbonyl compounds are converted into amines., , This reaction is called the reductive amination of aldehydes. Using this reductive, amination the 1° amine to 2° amines can be formed., , 4. By the reduction of amides: Amides yield primary amines on reduction by lithium, aluminum hydride, while N‐substituted and N, N‐disubstituted amides produce, secondary and tertiary amines, respectively., , B. Additional methods for the preparation of primary amines:, 1. By the reduction of nitroarenes: Aromatic amines are normally prepared by the, reduction of corresponding nitroarenes in presence of hydrogen and Raney nickel, tin, and hydrochloric acid, iron and hydrochloric acid, zinc and acetic acid, or ammonium, hydrogen sulphide., , UTTARAKHAND OPEN UNIVERSITY, , Page 308
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (i) Catalytic reduction: Nitro compounds are reduced to amines with hydrogen gas in, presence of powdered nickel., , (ii) Reduction with Sn/HCl, or Fe/HCl, or Zn/CH3COOH: Nitro compounds are also, reduced with metal and concentrated hydrochloric acid like Sn/HCl, Fe/HCl, or, Zn/CH3COOH into amines., , (iii) Partial reduction with NH4HS : By partial reduction, one of two nitro groups in a, dinitro compound is reduced into amino group by using ammonium hydrogen sulphide, as reducing agent., , 2. By the reduction of nitriles or cyanides: The carbon-nitrogen triple bond in a nitrile, or cyanide can be reduced by the reaction of hydrogen gas in presence of a metal, catalyst like nickel, palladium or lithium aluminium hydroxide., For example, methyl nitrile is reduced by hydrogen and nickel to ethyl amine., , UTTARAKHAND OPEN UNIVERSITY, , Page 309
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Phenyl methyl cyanide is reduced by hydrogen and nickel or by lithium aluminium, hydroxide to phenyl ethyl amine., , 3. By the action of ammonia on phenol: Mono aryl amines are prepared by the, reaction of ammonia on phenols in presence of zinc chloride at 300 ºC., , 4. By Schmidt reaction: Aromatic amines can be obtained by the treatment of aromatic, carboxylic acid in concentrated sulphuric acid with chloroform solution of hydrazoic, acid., , 5. By the reduction of oximes : Oximes yield primary amines on reduction by sodium, and ethanol or by lithium aluminium hydroxide (LiAlH4)., CH3CH, , NOH + 4[H], , Na, Alcohol, , Acetaldoxime, , UTTARAKHAND OPEN UNIVERSITY, , CH3CH2NH2 + H2O, Ethanamine, , Page 310
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 6. By the action of chloramine with Grignard’s reagent: The primary amines can be, obtained by the action of chloramines on Grignard’s reagent., For example, methyl amine is prepared by the action of chloramines on methyl, magnesium bromide., , 7. By the decarboxylation of amino acids: When an amino acid is heated with, Ba(OH)2, it loses CO2 to form a primary amine. For example:, , 8. By Hofmann’s bromamide synthesis: Hofmann bromination reaction is an organic, reaction used to convert a primary amide to a primary amine using bromine in an, aqueous or ethanolic solution of sodium hydroxide. This reaction is as:, , For example, acetamide reacts with bromine and potassium hydroxide to form methyl, amine., , UTTARAKHAND OPEN UNIVERSITY, , Page 311
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Similarly,, , Mechanism: The reaction mechanism involves several steps:, 1. The hypobromite ion OBr- anion is produced by the reaction of alkali with bromine., 2. The anion reacts with amide to give bromamide., 3. Base abstraction of the remaining amide proton gives a bromoamide anion., 4. The bromoamide anion rearranges as the R group attached to the carbonyl carbon, migrates to nitrogen at the same time the bromide ion leaves, giving an isocyanate, (step 4 and 5)., 5. The isocyanate adds water in a nucleophilic addition step to yield a carbamic, acid after that carbamic acid spontaneously loses CO2 to yield amine., , UTTARAKHAND OPEN UNIVERSITY, , Page 312
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9. By Gabriel’s phthalimide reaction: This method is used for the preparation of, primary amines. Phthalimide on reaction with ethanolic potassium hydroxide, gives potassium salt of phthalimide, which on heating with alkyl halide followed by, alkaline hydrolysis forms the corresponding primary amine., , UTTARAKHAND OPEN UNIVERSITY, , Page 313
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ORGANIC CHEMISTRY-II, , BCHCH-202, , C. Additional methods for the preparation of secondary amines, 1. By reduction of alkyl isocyanide or isocyanates: Isocyanide or isocyanates are, reduced to secondary amines with hydrogen gas in presence of Na/C2H5OH., , CH3NC, , +, , H2, , Na/C2H5OH, , CH3NHCH3, , 2. By reduction of N-substituted amides: Secondary amides can be reduced to amines, by a strong oxidizing agent like lithium aluminium hydroxide by the conversion of C=O, group to –CH2. Amides cannot be reduced by the less reactive NaBH4., , 3. By heating phenol with aniline: Secondary aromatic amines are prepared by heating, phenol with aniline in presence of anhydrous zinc chloride at 200 ºC., OH, , NH2, NH, ZnCl2, , +, , phenol, , 200 0C, , aniline, , diphenylamine, , D. Additional methods for the preparation of tertiary amines, 1. By reduction of N,N-disubstituted amides: N, N‐disubstituted amides yield tertiary, amines on reduction by lithium aluminum hydride., , UTTARAKHAND OPEN UNIVERSITY, , Page 315
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.11 REDUCTIVE AMINATION OF ALDEHYDIC AND, KETONIC COMPOUNDS, Aldehydes and ketones can be converted into primary, secondary and tertiary amines, using reductive amination in presence of ammonia or amine. The reaction is completed, in two steps. The first step is the nucleophiic addition of the carbonyl group to form an, imine. The second step is the reduction of the imine to an amine using a reducing, agent. A reducing agent employed commonly includes hydrogen and a catalyst such as, Ni, NaBH3CN (sodium cyanoborohydride), LiBH3CN (liyhium cyanoborohydride) etc., The general reductive reactions of aldehydes and ketones are as:, , Conversion of aldehyde or ketone into primary amine:, , For example, methyl ethyl ketone is reduced by ammonia in presence of nickel into 2amino butane., , Similarly, benzaldehyde is reduced with ammonia in presence of hydrogen and nickel, into benzylamine., , UTTARAKHAND OPEN UNIVERSITY, , Page 317
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Conversion of aldehyde or ketone into secondary amine:, , Conversion of aldehyde or ketone into tertiary amine:, , Mechanism:The sequential mechanism is as follow:, , UTTARAKHAND OPEN UNIVERSITY, , Page 318
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.12 IMPORTANT REACTIONS OF AMINES, As we know that amines are important class of organic compounds containing nitrogen, as one of the element in their composition. The amines are synthesized in pilot scale in, industries for many purposes i.e. as starting material for synthesis of other molecules,, synthesis of drug molecules, textile dyes, solvents etc. Both aliphatic and aromatic, amines undergo variety of chemical reactions. Though some has been described in, above, however some of the important reactions as being consolidately presented as, follow., , Reactions of aliphatic amines: Some of the important reactions of primary and, secondary amines like acylation,alkylation,formation of salts,sulphonation, reaction, with nitrous acid, reaction with carbondisulphide,reaction withGrignard reagent,, reaction with HOCl,oxidation reactions is being given as follow:, +, +, , HCl, CH3Br, , CH3CH2Cl, - HBr, , CH3CH2NHCH3, , CH3Br, , CH3CH2N(CH3)2, , OH, , CH3CH2NH2, , CH3Br, CH3CH2N+(CH3)2Br, , +, , CH3COCl, , CH3CH2NHCOCH3, N - ethylactamide, , UTTARAKHAND OPEN UNIVERSITY, , +, , HCl, , Page 319
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.13 SUMMARY, After studying this unit it can be summarized that this unit educate us about aliphatic, and aromatic derivatives of ammonia known as amines and are obtained by the, replacement of one, two or all three hydrogen atoms of ammonia by alkyl or aryl, groups. Classification of amines as primary, secondary and tertiary amines based on the, number of hydrogens replaced by alkyl or aryl groups.We learned about aromatic amino, compounds their types as aryl amines and arylalkyl amines. Aryl amines are those, compounds in which the –NH2 group is directly attached to the nucleus e.g., aniline, ptolidine etc. whereas in arylalkyl amines the –NH2 group is attached to a carbon atom of, the side chain e.g., benzylamine, β-phenylethylamine etc.We studied IUPAC, nomenclature of amines, physical and chemical properties of aliphatic and aromatic, amines in detail. As amines posses basic character, this unit also tells us about basic, characters pKb values indicating the basic strength and stereochemistry of amines.We, also studied various methods of preparation of primary, secondary and tertiary amines., The consolidated chemical reactions of aliphatic and aromatic reactions have also been, described in this unit., , 9.14 TERMINAL QUESTIONS, Section -A, Q.1 Long answered questions:, 5. What are amines? Describe the general methods of preparation of alkyl and aryl, amines., 6. Give the preparation, physical and chemical properties of acid anhydrides., 7. How can you prepared primary amines from: (i) Gabrial’s phthalimide reaction (ii), Wurtz reaction (iii) Hofmann’s bromamide method (iv) Curtius reaction., 8. Describe the general methods of preparation, physical and chemical properties of, amides., 9. Describe the mechanism of the acid and alkaline hydrolysis of esters., , UTTARAKHAND OPEN UNIVERSITY, , Page 325
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Section -B, Q.2 Sort answered questions, 10., , How can you distinguish between primary, secondary and tertiary amines?, , 11., , Why amines are basic in nature? Explain the role of substituents on the basicity, , of amines., 12., , Compare the reactivity of carboxylic acid derivatives towards nucleophilic, , substitution., 13., , How can you prepare secondary amines from isocynides?, , 14., , How can you prepare tertiary amines from tetra alkyl ammonium hydroxide?, , 15., , How can you synthesize primary and secondary amines by reductive amination, , of aldehydes?, 16., , Give the mechanism of reductive amination of aldehyde and ketones., , 17., , Explain the followings:, , (c), , Acetyl chloride has lower boiling point than acetic acid, , (d), , Acetyl chloride is more reactive than acetic anhydride, , 18., , How can you convert?, , (e), , Acyl chlorides into esters, , (f) Esters into amides, (g), , Amides into amines, , (h), , Amides into carboxylic acids, , 19., , How will you obtained:, , (e), , Primary amine from primary amide, , (f) Primary amine from phthalimide, (g), , Benzylamine from benzaldehyde, , (h), , Methylamine from methylisocyanate, , UTTARAKHAND OPEN UNIVERSITY, , Page 326
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Section –C, Q.3 Multiple choice questions (MCQs), 26., , 27., , 28., , 29., , 30., , Which functional group is present in a primary amine?, (a) -COOH, , (b) –NH2, , (c) C-O-C, , (d) -SH, , Which one of the followings is an amino compound?, a) CH3SH, , (b) CH3NHC2H5, , (c) CH3CH2NO2, , (d) CH3SCH3, , What is the IUPAC name of the given compound?, , (a) N, N-Dimethylaminomethane, , (b) N-ethyl-N-methyl aminoethane, , (c) Triethyl nitro, , (d) N- methylaminopropane, , The given structure is for, , (a) p-Toluidine, , (b) o-Toluidine, , (c) p-Methoxyaniline, , (d) p-Diaminobenzene, , All three amines can be obtained, (a) By Hofmann’s bromamide method., (b) By Curtius reaction., (c) By the decarboxylation of amines., (d) By reductive amination of aldehydes and ketones., , 31., , Amines are weak bases, (a) Because their boiling points are higher., (b) Because lower members are water soluble., , UTTARAKHAND OPEN UNIVERSITY, , Page 327
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ORGANIC CHEMISTRY-II, , BCHCH-202, , (c) Because they are volatile., (d) Due to the presence of unshared pair of electrons on nitrogen atom., 32., , 33., , 34., , The reduction of nitroalkane with Sn/HCl gives, (a) Tertiary amines, , (b) Primary amines, , (c) Secondary amines, , (d) All of these, , All three amines can be prepared by the reductive amination of, (a) Aldehydes and ketones, , (b) Carboxylic acids, , (c) Ethers and thioethers, , (d) Alcohols and thiols, , Aromatic amines are less basic than ammonia and aliphatic amines because, (a) They have (4n+2) π electrons., (b) They are more reactive., (c) The lone pair of electrons on nitrogen is partially shared with benzene ring., (d) Nitrogen does not have lone pair of electrons in aromatic amines., , 35., , Aromatic primary amines cannot be prepared by Gabriel’s phthalimide synthesis, because, (a) Aryl halides do not undergo nucleophilic substitution with anion formed by, phthalimide., (b) Aromatic amines are less basic than aliphatic amines., (c) Aryl halides are decomposed with phthalimide., (d) None of the above., , 36., , 37., , Reduction of nitrobenzene with Ni will produce, (a) Azoxybenzene, , (b) p-Aminophenol, , (c) m-Dinitrobenzene, , (d) Aniline, , Hofmann’s bromamide reaction is used to convert, (a) Primary amide to primary amines, (b) Alkyl halide to primary amine, (c) Aldehyde to primary amines, (d) Glycine to primary amines, , 38., , 39., , Tertiary amines cannot form hydrogen bonding because they, (a) Are stable, , (b) Are unstable, , (c) Are saturated hydrocarbons, , (d) Do not have hydrogen, , Which of the following gives a tertiary amine when treated with AgOH?, , UTTARAKHAND OPEN UNIVERSITY, , Page 328
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ORGANIC CHEMISTRY-II, , 40., , BCHCH-202, , (a) N-Methyl acetamide, , (b) Tetraethyl ammonium iodide, , (c) Acetone oxime, , (d) Phenyl methylcynide, , The major product (X) of the reaction is:, , (a) RNH2, , (b), , (c), , (d) (CH3)4N+Cl-, , 16. Methanol has the higher boiling point than methylamine because, (a) Methylamine is more basic than methanol., (b) Methylamine does not show hydrogen bonding., (c) Hydrogen bonding is stronger in methanol than in methylamine., (d) An unshared pair of electrons is present on nitrogen atom in amines., 17. Amines which are bonded in one alkyl group are, (a) Primary amine, , (b) Secondary amine, , (c) Tertiary amine, , (d) Quaternary amines, , 18. Aniline reacts with phenol in presence with zinc chloride at 200ºC to form, (a) Primary amine, , (b) Secondary amine, , (c) Tertiary amine, , (d) Quaternary amines, , 19. Chloramine reacts with methyl magnesium bromide to form, (a) Tertiary butyl amine, , (b) Ethyl methyl amine, , (c) Acyl amides, , (d) Methyl amine, , 20. Quaternary ammonium salts on hydrolysis with most silver produce, (a) Primary amine, , (b) Secondary amine, , (c) Tertiary amine, , (d) Azo compounds, , UTTARAKHAND OPEN UNIVERSITY, , Page 329
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 9.15 ANSWERS (MCQs), , 26., , (b), , 27., , (b), , 28., , (a), , 29., , (c), , 30., , (d), , 31., , (d), , 32., , (b), , 33., , (a), , 34., , (c), , 35., , (a), , 36., , (d), , 37., , (a), , 38., , (d), , 39., , (b), , 40., , (a), , 41., , (c), , 42., , (a), , 43., , (b), , 44., , (d), , 45., , (c), , 9.16 REFERENCES, Bahl, B.S, and Bahl A., Advanced organic chemistry, Chand & Company Ltd.,New, Delhi, 1993, , Roger Macomber, Organic Chemistry, Volume-2, University Science Books,, Sausalito, California, 1996., , F. Wild, Characterization of Organic Compounds, 2nd Edition, Cambridge University, Press, 2003., , K. S. Tewari, N. K. Vishnoi and S. N. Mehrotra, A Text Book of Organic Chemistry,, 2nd Revised Edition, Vikas Publishing House Pvt Ltd, New Delhi, 2003., , Stephen A. Lawrence, Amines: Synthesis, Properties and Applications, Cambridge, University Press, 2004., , Organic Chemistry, Pearson Education India, 2008., Ernest Hodgson, Michael Roe, Dictionary of Toxicology, 3rd Edition, Academic, Press, 2014., , Mehta, Bhupinder, Mehta, Manju, Organic Chemistry, 2nd Edition, PHI Learning, Pvt. Ltd., Delhi, 2015., , Robert J. Ouellette, J. David Rawn, Principles of Organic Chemistry, Academic, Press, Elsevier, Amsterdam, Netherlands, 2015., , . David Ginsburg, Concerning Amines: Their Properties, Preparation and Reactions,, Pergamon Press, Elsevier, 2016., , UTTARAKHAND OPEN UNIVERSITY, , Page 330
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ORGANIC CHEMISTRY-II, , BCHCH-202, , UNIT-10 ORGANOSULPHUR AND, ORGANOPHOSPHORUS COMPOUNDS, CONTENTS:, 10.1, , Objectives, , 10.2, , Introduction, , 10.3, , Preparation of organosulphur compounds, , 10.4 Thiols and thioethers, 10.5 Preparation of thiols and thioethers, 10.6 Physical properties of thiols and thioethers, 10.7 Chemical properties of thiols and thioethers, 10.8 Biological role of organosulphur compounds, 10.9 Preparation of organophosphorus compounds, 10.10 Nomenclature of organophosphorus compounds, 10.11 Physical properties of organophosphorus compounds, 10.12 Chemical properties of organophosphorus compounds, 10.13 Pentavalent organophosphorus compounds, 10.14 Organophosphoranes,phosphoylids: Wittig reagent, 10.15 Biological role of organophosphorus compounds, 10.16 Summary, 10.17 Terminal questions, 10.18 Answers(MCQs), 10.19 Reference, , 10.1 OBJECTIVES, The learning objective of this important unit are to study the organosulphur compounds, like thiols/mercaptans, thioethers and organophosphorus compounds like phosphine,, phosphorane, phosphine oxides, their preparation, physical properties and chemical, reactions. Because of the importance of sulphur and phosphorus for living system, the, aim of this unit is also to study the biological role of organosulphur and, organophosphorus compounds., , UTTARAKHAND OPEN UNIVERSITY, , Page 331
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 10.2 INTRODUCTION, The organosulphus and organophosphorus compounds are very important class of, organic compounds. These compounds are found in manyb living things in the form of, amino acids, nucleotides, co-enzymes etc. These classes of compounds can be, introduced separately as follow:, , A. Organosulphur compounds: Organosulfur compounds are organic compounds that, contain sulphur. They are found in all living systems in the form of certain essential, amino acids (e.g., cystine, methionine), peptides (e.g., glutathione), coenzymes (e.g.,, coenzyme-A, lipoic acid), vitamins (e.g., thiamine, biotin), and hormones. They also, include various bioactive synthetic compounds such as sulpha drugs, antibiotics, (penicillin’s, cephalosporins, bacitracin, gliotoxin etc.), alkaloids, insecticides,, fungicides, poisons (sulphur mustard) and various classes of dyes. Fossil fuels like coal,, crude oil and natural gas contain organosulphur compounds. Organosulphur compounds, may have a sulphur-hydrogen, sulphur-oxygen, sulphur-nitrogen, or a sulphur-halogen, bond. The sulphur atom in these compounds may be in –2, +4, and +6 oxidation states., There are three main classes of organosulphur compounds:, 1. The first class of organosulphur compounds contains sulphur atom in the -2 oxidation, state. They include mercaptans (thiols, R-SH), thioethers (R-S-R′), thiophenols (ArSH),, , thioaldehydes, , (R-CH=S),, , and, , thioketones, , (R-CS-R′),, , disulphides, , and, , polysulphides (R-Sx-R′), and sulphonium salts (RR′S+X-, where X is a halogen ion)., 2. The second class of organosulphur compounds contains sulphur atom in +4 oxidation, state e.g., sulphinic acids (R-SO2H, or R-SO(OH)) and sulphoxides (R-SOR′)., 3. The third class of organosulphur compounds contains sulfur atom in the +6 oxidation, state e.g, sulphonic acids (R-SO3H) and sulphones (R-SO2-R′)., , B. Organophosphorus compounds: Organophosphorus compounds are organic, derivatives of phosphorus which usually contain a phosphoryl (P=O) or a, thiophosphoryl (P=S) bond. These compounds are usually esters, amides, or thiol, derivatives of phosphoric, phosphonic, phosphinic, or thiophosphoric acids. These, , UTTARAKHAND OPEN UNIVERSITY, , Page 332
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 4. From Grignard’s reagents: Grignard’s reagent on treatment with sulphur and, followed by the hydrolysis in presence of an acid gives the corresponding thiols. The, general equation is as:, , For example, ethyl magnesium bromide on treatment with sulphur and followed by the, hydrolysis in presence of an acid gives ethanethiol., , B. General methods for preparation of thioethers: Thioethers can be prepared by the, following general methods., , 1. From ethers: Thiothers can be prepared by heating ethers with phosphorous, pentasulphide. For example, dimethyl ether on heating with phosphorous pentasulphide, forms dimethyl sulphide., , Similarly, ethyl methyl ether on heating with phosphorous pentasulphide produces ethyl, methyl sulphide., , 2. From thiols: Thioethers can be obtained by the treatment of thiols with olefins in the, presence of peroxides. For example, methanethiol on reaction with propylene in, presence of peroxide forms methyl-n-propyl sulphide., , UTTARAKHAND OPEN UNIVERSITY, , Page 338
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 10.6 PHYSICAL PROPERTIES OF THIOLS AND, THIOETHERS, A. Physical properties of thiols: Except methanethiol which is a gas, the higher thiols, are volatile liquids having extremely unpleasant odors, as garlic and rotten eggs., Methanthiol or ethanethiol is purposely added to LPG cylinders and natural gas in order, to reveal leaks. Thiols, unlike alcohols, do not form hydrogen bonds (S-H bonds are less, polar than O-H bonds), therefore they have lower boiling points than to corresponding, alcohols (Table-10.4). Thiols are insoluble in water due to the absence of hydrogen, bonding with water, but readily soluble in organic solvents like ether and alcohol. They, are more easily oxidized than alcohols; oxidation takes place at sulphur. Thiols (pKa =, 7) are more acidic than alcohols (pKa = 16), and their proton can be removed by the, reaction with base., , Table 10.4: Boiling points of thiols and corresponding alcohols, Thiols / alcohols, , Boiling points (ºC), , CH3SH, , 6, , CH3OH, , 56, , C2H5SH, , 35, , C2H5OH, , 78, , C3H7SH, , 68, , C3H7OH, , 98, , B. Physical properties of thioethers: Thioethers are colourless, oily liquids having an, unpleasant order. The boiling points of thioethers are more than those of corresponding, ethers. The boiling point of dimethyl thioether is 38ºC, whereas the boiling point of, , UTTARAKHAND OPEN UNIVERSITY, , Page 340
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ORGANIC CHEMISTRY-II, , BCHCH-202, , Similarly, reaction of ethanethiol with acetone in presence of hydrochloric acid results, the formation of diethyl methyl mercaptol., , 3. Reactions with alkali metals and alkali: On reaction with alkali metals, thiols form, mercaptides with the evolution of hydrogen gas., , 4. Reactions with metal salts and metallic oxides: Thiols on reaction with metal, oxides and other metal salts form the following salts:, 2C2H5SH + (CH3COO)2Pb, Lead acetate, , (C2H5S)2Pb + 2CH3COOH, Lead diethyl, mercaptide, , Ethanethiol reacts with mercuric chloride to form a precipitate of mercury diethyl, mercaptide. This reaction is used to distinguish between ethane thiol and ethyl alcohol,, ethyl alcohol does not give this reaction., , UTTARAKHAND OPEN UNIVERSITY, , Page 342
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 5. Oxidation with mild oxidizing agents: With mild oxidizing agents like chlorine,, hydrogen peroxides, the thioethers are oxidized into sulphoxides. For example, the, dimethyl sulphide oxidized with hydrogen peroxide into dimethyl sulphoxide., , 6. Oxidation with strong oxidizing agents: When oxidized with strong oxidizing, agents, like concentrated nitric or potassium permanganate, thioethers are converted, into sulphones. For example, dimethyl sulphide is oxidized by the KMnO4 into, dimethyl sulphone., O, CH3-S-CH3, , KMnO4, , CH3, , S, , CH3, , O, Dimethyl sulphide, , Dimethyl sulphone, , 10.8 BIOLOGICAL ROLE OF SULPHUR COMPOUNDS, Organosulphur compounds such as diallyl disulfide, diallyl trisulfide and S-ally cysteine, are used as therapeutics. They can be used as inhibitors of polymerization and, oxidation, stabilizers of polymer materials, and as solvents. The sulphonic acids and, their salts are used an intermediates in heavy organic synthesis and as surfactants. Most, organosuphur compounds are highly toxic and are used as insecticides, fungicides and, poisons. Vitamin B1 plays an important role, as a co-enzyme in the decarboxylation of, pyruvate and also in the formation of another co-enzyme the co-enzyme A which is a, key enzyme for the degradation of glucose. Besides this many drugs contain sulphur as, one of the element in their structure. The sulpha drugs are widely used as anti-bacterial, agents by mimicking p-aminobenzoic acid. The common drugs in use are as follow., Penicillin is also a sulphur containing drug., , UTTARAKHAND OPEN UNIVERSITY, , Page 345
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 10.15 BIOLOGICAL ROLE OF PHOSPHORUS, COMPOUNDS, The organophosphorus compounds have several industrial, agricultural, medicinal, properties; they are used in synthesis of alkenes by the Witting reaction and as, anthelmintics. They are potentially toxic and used as insecticides, fungicides, herbicides, in agriculture worldwide.The organophosphate group is the largest group of insecticide, among agrochemicals. The O.P. insecticides are also biodegradable like malathion and, parathion. Organophosphorus compounds e.g. neguvon, ruelene, dioxathion, diazinon, etc. are used in veterinary medicine for control the animal disease e.g. ticks. These, organic phosphorous compounds such as sarin and tabun are developed as nerves agents, that are most dangerous and may be used as chemical warfare agents.These compounds, block activity of acetulcholinesterase. Phosphorus compounds play key role in living, system. They are essential for energy transfer (ATP-ADP + E), DNA, the genetic, material is made up of nucleotide which contains phosphorus as one of the element in, its structural framework., , O, , CH3, CH O, CH3, , P, , F, , CH3, , O, , CH3, N, , H3CO, , P, , P, , CH3, , sarin, , O, , O, , C N, , OCH2CH3, tabun, , O, S, , OCH3, , CH C O CH2CH3, CH2, , C O CH2CH3, , S, CH3CH2O, , P O, , NO2, , OCH2CH3, , O, malathion, , UTTARAKHAND OPEN UNIVERSITY, , parathion, , Page 355
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 10.16 SUMMARY, At the end of this unit it can be summarized that the organophosphorus and, organosulphur compounds find very important place in organic chemistry. Regarding, these compounds the present unit educates us about organic compounds containing, sulphur like thiols, the sulphur analogue of alcohols having –SH functional group. The, –SH functional group is known as sulfhydral or mercapto group. Examples are CH3SH, (methanethiol),, , C2H5SH, , (ethanethiol),, , CH3CH2CH2SH, , (propane-1-thiol),, , CH3CHSHCH3 (propane-2-thiol). Thioethers the sulphur analogue of ethers with the, genral formula R-S-R'. Some examples of thioethers are CH3SCH3 (dimethyl sulphide),, C2H5SCH3 (ethyl methylsulphide), C2H5SC2H5 (diethyl sulphide) etc.We learned about, method of preparation, physical and chemical reaction alonwith the biological role of, organosulphur compounds. This unit also describes the preparation, nomenclature,, physical and chemical properties of organophosphorus compounds with their biological, role., , 10.17 TERMINAL QUESTIONS, Section -A, Q.1. Long answered questions, 10. What are thiols? Describe the general methods of preparation and chemical, properties of thiols., 2 What are thioethers? Describe the general methods of preparation, physical and, chemical properties of thioethers., 3 What are organophosphorus compounds? Discuss methods for the synthesis of, organophosphorus compounds., 4 Discuss biological role of organophosphorus and organosulphur compounds with, some examples, 5 Discuss nomenclature of organosulphur and organophosphorus compounds., , Section -B, , UTTARAKHAND OPEN UNIVERSITY, , Page 356
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ORGANIC CHEMISTRY-II, (c) Acid anhydrides, 18., , 19., , BCHCH-202, (d) All of these, , On reaction with hydrogen peroxide thioethers gives, (a) Sulphones, , (b) Sulphoxides, , (c) Disulphides, , (d) Sulphinic acid, , Thiols undergo desulphurization with Raney nickel gives, (a) Ethane, (c) Methane, , 20., , (b) Hydrogen peroxide, (d) Thioethers, , Thioethers are hydrolyzed with boiling sodium hydroxide into, (a) Mercatols, (c) Thioethers, , (b) Carboxylic acids, (d) Alcohols, , 21. The organophosphorus compounds are prepared by:, (a) Arbusov reaction, (c) Wittig reaction, , (b) Perkin reaction, (d) All of them, , 22. Pentahydride of phosphorus is known as, (a) Phosphine, , (b) Phophorane, , (c) Phosphine oxide, , (d) phosphinic acid, , 23. Which is phosphorus containing compound?, (a) Diethyl thioether, , (b) ATP, , (c) Malathion, , (d) both b and c, , 24. Penicillin is a;, (a) Organic compound containing phosphorus, (b) Organic compound containing aluminium, (c) Organic compound containing Sn, (d) None of them, 25. Wittig reagent is:, (a) Phosphorus containing organic compound, (b) Nitrogen containing organic compound, (c) Sulphur containing organic compound, (d) Both sulphus and nitrogen containing compound, , UTTARAKHAND OPEN UNIVERSITY, , Page 360
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ORGANIC CHEMISTRY-II, , BCHCH-202, , 10.18 ANSWERS (MCQs), , 1., , (d), , 2., , (c), , 3., , (a), , 4., , (b), , 5., , (d), , 6., , (a), , 7., , (c), , 8., , (a), , 9., , (b), , 10., , (d), , 11., , (a), , 12., , (c), , 13., , (d), , 14., , (c), , 15., , (a), , 16., , (b), , 17., , (d), , 18., , (b), , 19., , (a), , 20., , (d), , 21., , (a), , 22., , (b), , 23., , (d), , 24., , (a), , 25., , (a), , 10.19 REFERENCES, 1. Mukharji, S.M., Singh S.P., Kapoor R.P. Organic Chemistry Volume-II Wiley, Eastern, Ltd. New Delhi. 1993., 2. R. L. Madan, Organic Chemistry, Tata McGraw-Hill Education Pvt. Ltd., New, Delhi, 1972., 3. James Ralph Hanson, Functional Group Chemistry, Basic Concepts in, Chemistry, Volume 6 of Tutorial chemistry texts, Royal Society of Chemistry,, 2001., 4. Stanley E. Manahan, Toxicological Chemistry and Biochemistry, 3rd edition,, CRC Press, USA, 2002., 5. Tadashi Okuyama, Howard Maskill, Organic Chemistry: A Mechanistic, Approach, OUP Oxford, 2013., 6. Eric Block, Reactions of Organosulfur Compounds: Organic Chemistry: A, Series of Monographs, Volume 37, Academic Press, New York, 2013., 7. Mehta, Bhupinder, Mehta, Manju, Organic Chemistry, 2nd Edition, PHI, Learning Pvt. Ltd., Delhi, 2015., , UTTARAKHAND OPEN UNIVERSITY, , Page 361
