Amines Test - 4

C₆H₅SO₂Cl₂.This is benzenesulphonyl chloride is known hinsberg reagent. It is used to distinguish between primary, secondary and tertiary amine.

p – toluenesulphonyl chloride can also be used instead of benzene-sulphonyl chloride to distinguish between 1⁰, 2⁰, 3⁰amines. Also, the product with a primary amine is soluble in alkali, the product with secondary amine is insoluble in alkali and tertiary amine does not give any reaction, therefore we can isolate and distinguish between primary, secondary and tertiary amines.

In carbylamines reaction, primary amine reacts with chloroform and base to form isocyanide having foul smell.

Alkyl amines and ammonia are more basic than aniline because in aniline lone pair on N is in resonance with benzene ring so is less available.
Also more 2⁰ alkyl amines are more basic than primary amine and ammonia due to +I effect of the alkyl group which increases basicity.

The activating power of aniline can be controlled by acetylation of -NH₂ group by acetic anhydride or acetyl chloride to protect the -NH₂ group. This will give para nitro product as the major product, instead of o,m,p mixture that we get if we do direct nitration of aniline.

C₆H₅NH₂ + CH₃COCl  → C₆H₅NHCOCH₃

C₆H₅NHCOCH₃  + conc HNO₃  + H₃O⁺ ----> p-nitroaniline (major) + o-nitroaniline (minor)

Only primary amines undergo carbylamine reaction (isocyanide test) because only they can form isocyanide with chloroform and alc.KOH.

RNH₂ + CHCl₃ + 3KOH ----> RNC (foul smell) + 3KCl + 3H₂O

Amines behave as Lewis base because of the presence of lone pair on N, whereas in amides and cyanides the lone pair on nitrogen is involved in resonance. In esters, the lone pair on oxygen is involved in resonance.

An amine molecule has the shape of a somewhat flattened triangular pyramid, with the nitrogen atom at the apex. An unshared electron pair is localized above the nitrogen atom.