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Monday, 27 February 2017

Amines III


Reactions of amines:

(a) Acylation Reaction: Aliphatic and aromatic primary and secondary amines (which contain replaceable hydrogen atoms) react with acid chlorides, anhydrides and esters to form substituted amide. 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, like pyridine, which removes HCl formed and shifts the equilibrium to the product side.

Since tertiary amine do not contain replaceable hydrogen atom they do not undergo acylation reaction.

(b) Carbylamine reaction: Only aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines.
Secondary and tertiary amines do not give the above test.

(c) Reaction of primary amine with nitrous acid:


(i) Primary aliphatic amine on reaction with nitrous acid (HNO2) forms aliphatic diazonium salt which decomposes to form alcohol and evolve nitrogen.
(ii) Primary aromatic amines react with nitrous acid (HNO2) in cold (273-278 K)
to form diazonium salt.
(d) Reaction with benzene sulphonyl chloride: Hinsberg’s reagent-Benzenesulphonyl chloride (C6H5SO2Cl) reacts with primary and secondary amines to form sulphonamides.
The hydrogen attached to nitrogen in sulphonamide formed by primary amine is strongly acidic due to the presence of strong electron withdrawing sulphonyl group. Hence, it is soluble in alkali.
Since sulphonamide formed by secondary amine does not contain any hydrogen atom attached to nitrogen atom, so it is not acidic. Hence it is insoluble in alkali.

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