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•, , where R, R’ may be alkyl or aryl., Preparation of ketones:, a) By oxidation of alcohols:, Oxidation of secondary alcohols in presence of oxidizing agent like K2Cr2O7/H2SO4,, KMnO4, CrO3 gives ketones., R', |, , R', |, , Oxidation, K 2Cr2O7 / H 2 SO4, , R −0 C − OH → R − C = O, Ketone, , 2 Alcohol, , b) By dehydrogenation of alcohols:, , When the vapours of a secondary alcohol are passed over heated copper at 573 K,, dehydrogenation takes place and a ketone is formed., Cu /573 k, R − CH − R ' , → R − C− R ', |, OH, , ||, O, , c) By hydration of alkynes:, , Alkynes on hydration with HgSO4/dil.H2SO4 at 333 K form ketones., 2+, , +, , Hg / H 333 k, Isomerisation, CH 3 − C ≡ CH + H − OH , → CH 3 − C = CH 2 , → CH 3 − C − CH 3, |, , OH, , ||, , O, Pr opanone, , d) From acyl chloride:, , Acyl chloride on treatment with dialkyl cadmium (prepared by reaction of cadmium, chloride with Grignard reagent) gives ketone., 2 R − Mg − X + CdCl2 → R2Cd + 2Mg ( X )Cl, , 2 R '− C − Cl + R2Cd → 2 R '− C − R + CdCl2, ||, O, , ||, O, , e) From nitriles:, , Nitriles on treatment with Grignard reagent followed by hydrolysis give ketones., , f) By Friedel Crafts acylation reaction:, , Benzene or substituted benzene on treatment with acid chloride in presence of, anhydrous aluminium chloride forms ketone., , Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks

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g) Preparation of aldehydes and ketones by ozonolysis of alkenes:, , •, , •, , Reactions of aldehydes and ketones:, a) Aldehydes are generally more reactive than ketones in nucleophilic addition, reactions due to steric and electronic reasons (or inductive effect)., b) Electronic Effect:, Relative reactivities of aldehydes and ketones in nucleophilic addition reactions is, due the positive charge on carbonyl carbon. Greater positive charge means greater, reactivity. Electron releasing power of two alkyl groups in ketones is more than one, in aldehyde. Therefore positive charge is reduced in ketones as compared to, aldehydes. Thus ketones are less reactive than aldehydes., c) Stearic Effect:, As the number and size of alkyl group increase, the hindrance to the attack of, nucleophile also increases and reactivity decreases. In aldehydes there is one alkyl, group and one hydrogen atom, whereas in ketones there are two alkyl groups (same, or different)., Nucleophilic addition reactions of aldehydes and ketones:, (a)Addition of hydrogen cyanide (HCN) to form cyanohydrins, , (b)Addition of sodium hydrogensulphite (NaHSO3) to form bisulphate addition, compound, , Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks

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(c)Addition of Grignard reagent (RMgX) to form alcohol, , (d)Addition of alcohol:, (i) Aldehydes on addition of monohydric alcohol in presence of dry HCl forms hemiacetal, and acetal., , (ii)Ketones do not react with monohydric alcohols. Ketones react with ethylene glycol, under similar conditions to form cyclic products known as ethylene glycol ketals., , (e)Addition of ammonia and its derivatives:, , •, , Reduction of aldehydes and ketones:, (a) Reduction to alcohols:, Aldehydes and ketones on catalytic hydrogenation in presence of Ni, Pt or Pd by using, lithium aluminium hydride (LiAlH4) or sodium borohydride (NaBH4 ) forms primary and, secondary alcohols respectively., , \, /, , H 2 / Ni , Pt or Pd, Or, LiAlH 4, Or, NaBH 4, , C = O → /\CH − OH, , Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks

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(vii) From acyl halides and anhydrides: Acid chlorides when hydrolysed with water give, carboxylic acids .On basic hydrolysis carboxylate ions are formed which on further, acidification forms corresponding carboxylic acids. Anhydrides on hydrolysis forms, corresponding acid(s), , (viii)From esters: Acidic hydrolysis of esters gives directly carboxylic acids while basic, hydrolysis gives carboxylates, which on acidification give corresponding carboxylic, acids., H 3O +, , R − COO − R ' ⇔ R − COOH + R '− OH, NaOH, , R − COO − R ' ⇔ R − COO+ − Na + R '− OH, ↓ H 3O, R −COOH, , •, , Physical properties of carboxylic acids:, (i)Solubility: As the size of alky group increases solubility of carboxylic acid decreases, because non-polar part of the acid increases, (ii)Boiling points: Carboxylic acids are higher boiling liquids than aldehydes, ketones, and even alcohols of comparable molecular masses. This is due to extensive association, of carboxylic acid molecules through intermolecular hydrogen bonding., , •, , Acidity of carboxylic acids:, Carboxylic acids are more acidic than phenols. The strength of acid depends on extent of, ionization which in turn depends on stability of anion formed., (i)Effect of electron donating substituents on the acidity of carboxylic acids: Electron, donating substituent decreases stability of carboxylate ion by intensifying the negative, charge and hence decreases acidity of carboxylic acids., , Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks

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NaOH &CaO / Heat, R − COONa , → R − H + Na2CO3, , (c)Reactions involving substitution reaction in hydrocarbon part:, (i) Hell-Volhard-Zelinsky reaction: Carboxylic acids having an α -hydrogen are, halogenated at the α -position on treatment with chlorine or bromine in the presence of, small amount of red phosphorus to give α -halocarboxylic acids), X 2 /Re d phosphorus/H 2O, R − CH 2 − COOH →, R − CH − COOH, |, X, X =Cl , Br, α − Halocarboxylic acid, , (ii)Ring substitution in aromatic acids: Aromatic carboxylic acids undergo electrophilic, substitution reactions. Carboxyl group in benzoic acid is electron withdrawing group, and is meta directing., , a), , b), , Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks