1. Carbylamine reaction
Primary amines (both aliphatic and aromatic) when heated with chloroform and ethanolic potassium hydroxide form isocyanides (also known as carbylamines) which have a foul smell. This reaction is called carbylamine reaction and is used as a test for primary amines. Secondary and tertiary amines do not show this reaction.
2. Diazotisation:
Aromatic amines react with nitrous acid (HNO2) at low temperature (273-278 K) to form diazonium salts. The process is known as diazotisation eg.
3. Hofmann’s bromamide reaction:
In this reaction, an acid amide is heated with Br2 and aq. NaOH when 1° amine having one carbon atom less is produced. This involves migration of alkyl or aryl group from carboxyl carbon of the amide to nitrogen atom of the amine. The amine so formed contains one carbon less than that present in amide.
4. Coupling reaction:
Diazonium salts react with phenol and amines to give azo compounds which have an extended conjugate system having both the aromatic rings joined by -N = N – bond.
eg.
5. Gabriel phthalimide synthesis:
This method is used for preparing only 1° amines. In this method, phthalimide is treated with alcoholic KOH to give potassium phthalimide, which is treated with alkyl halide or benzyl halide to form N- alkyl or aryl phthalimide. The hydrolysis of N- alkyl phthalimide with 20% HCI under pres¬sure or reuxing with NaOH gives 1° amines.
The more convenient method is by the treatment of alkyl phthalimide with hydrazene.
Phthalic acid can again be converted into phthalimide and is used again and again. This method is very useful because it gives pure amines.
