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Organic Compounds Containing Nitrogen, Organic compounds containing nitrogen or amines are an important class of organic compounds, formed by replacing one or more hydrogen atom of ammonia by alkyl or aryl group. They exist in, nature in various forms like proteins, vitamins, hormones, etc. In the form of amino acids, these, amines are very important for our body. According to the IUPAC system, the naming of the amines is, done by first naming the alkyl group and then add amine in the end, for example, methylamine., Aromatic amines are named as the derivative of the simplest aromatic amine i.e., aniline, for example,, 2-Bromoaniline., In this chapter, you will study the structures of different types of amines, their preparation, physical, properties, chemical reactions, etc. In real life, we see compounds of amines in bulk form but we, hardly become inquisitive in their formation and chemical properties. This chapter explains all those, questions. Thus, in the real world, amines are largely used for many applications as follows:, Methylamines are used for making various agricultural products such as herbicides, insecticides,, miticides, etc., There are various kinds of amines such as MEA, DEA, DGA, and others are used in industries for, removing carbon dioxide and hydrogen sulphide., Aromatic amines are used for the production of dyes., Amines are used in various kinds of drugs such as chlorpheniramine, ephedrine, amitriptyline, etc., , Structure of Amines:, In amines, the nitrogen is in sp3 hybridization with 3 sigma, bonds and 1 lone pair of electrons. Amines possess the, tetrahedral geometry but the bond angle in its structure is, always less than 109.50 because nitrogen atom has a lone, pair of electrons which reduces its bond angle., General structure of amines, , Classification of Amines, Amines can be classified into three categories as follows, depending on the number of alkyl or aryl, groups attached to the nitrogen atom:
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Classification of amines, , Physical Properties, •, •, •, •, •, , Lower aliphatic amines are gases with a fishy smell and higher aliphatic amines are liquid., Lower aliphatic amines are soluble in water because of the capability of hydrogen bonding, with the water molecules., Amines are soluble in organic solvents as well such as alcohol, ether, and benzene, etc., The boiling point of amines follows this order below:, Primary > Secondary> Tertiary, Intermolecular interaction of amines is prevalent in primary amines than in secondary amines, and this interaction is absent in tertiary amines., , Preparation of Amines:, Amines can be prepared using the following methods:, Reduction of Nitro Compounds, Nitro compounds on reduction with hydrogen gas in the presence of finely divided nickel. palladium, or platinum and also on reduction with metals in acidic medium give amines., , Ammonolysis (Hoffmann’s method), The process of cleavage of the C-X bond by ammonia molecule is known as ammonolysis., The order of reactivity of halides with amines is RI >RBr > RCl, Reduction of Nitriles, Nitriles on reducing with LiAlH4 or catalytic hydrogenation produce primary amines., This method is used for preparing amines containing one carbon atom more than the starting amine.
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Reduction of Amides, Amides on reducing with LiAlH4 yield amines., Gabriel phthalimide synthesis, This method is used for the preparation of primary amines., Phthalimide on reacting with ethanolic solution of KOH forms potassium salt of phthalimide which, on heating with alkyl halide followed by alkaline hydrolysis yields the corresponding primary amine., Hoffmann bromamide degradation reaction, In this method, primary amines are prepared by treating an amide with bromine in an aqueous or, ethanolic solution of NaOH., In this degradation reaction, migration of alkyl or aryl group takes place from carbonyl carbon of the, amide to the nitrogen atom., The amine formed has one carbon atom less than the starting amide., Reaction of Amines, Acylation reaction, The process of introducing an acyl group (R–CO–) into the molecule is called acylation., The reaction is carried out in the presence of a stronger base than the amine, such as pyridine, which, removes HCl formed and shifts the equilibrium to the product side., Carbylamine reaction, On heating aliphatic and aromatic primary amines with chloroform and ethanolic KOH they form, isocyanides or carbylamines which have foul odour., Secondary and tertiary amines do not show this reaction. This reaction is used as a test for primary, amines., , Reaction with Nitrous acid, Primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts., Aromatic amines on treating with nitrous acid at low temperatures to form diazonium salts which are, used in the synthesis of a variety of aromatic compounds., Secondary and tertiary amines react with nitrous acid in a different manner., Reaction with arylsulphonyl chloride, Heinsberg’s reagent or benzene sulphonyl chloride (C6H5SO2Cl) reacts with primary amines and, secondary amines to form sulphonamides., Primary amine reacts with benzene sulphonyl chloride to form N-ethylbenzene sulphonyl amide.
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With secondary amine,N,N-diethyl-benzenesulphonamide is formed., N, N-diethylbenzene sulphonamide does not contain any H atom attached to nitrogen atom so it is not, acidic and is therefore insoluble in alkali., Tertiary amines do not react with benzenesulphonyl chloride., The reaction of amines with benzenesulphonyl chloride in a different manner is used for the, distinction of primary, secondary and tertiary amines., Electrophilic substitution, Ortho- and para-positions to the -NH2 group become centres of high electron density., So -NH2 group is ortho and para directing and a powerful activating group., Bromination, Aniline reacts with bromine water at room temperature to give a white precipitate of 2, 4, 6tribromoaniline., , Nitration, Nitric acid is a nitrating agent plus a good oxidising agent. So direct oxidation of aromatic amines is, not useful since it gives tarry oxidation products along with some nitro derivatives., In strong acidic medium, aniline is protonated to form the anilinium ion which is meta directing., Hence besides the ortho and para derivatives, significant amount of meta derivative is also formed., Sulphonation, Aniline on reacting with sulphuric acid forms anilinium hydrogen sulphate which on heating with, sulphuric acid at 453-473K gives p-aminobenzene sulphonic acid as the major product., Reactions involving displacement of Nitrogen, Diazonium group is a very good leaving group and is substituted by other groups such as Cl-, Br-,I,CN- and OH- which displace nitrogen from the aromatic ring. The nitrogen released from the, reaction mixture escapes as a gas., Replacement by halide or cyanide ion:, This reaction is called Sandmeyer reaction in which nucleophiles like Cl-,Br- and CN- can be easily, introduced in the benzene ring in the presence of Cu(I) ion., , Alternatively, chlorine or bromine can also be introduced in the benzene ring by treating the, diazonium salt solution with corresponding halogen acid in the presence of Cu powder. This is
