(i) Methylamineand dimethylamine can be distinguished by the carbylamine test.
Carbylamine test: Aliphatic and aromatic primary amines onheating with chloroform and ethanolic potassium hydroxide form foul-smellingisocyanides or carbylamines. Methylamine (being an aliphatic primary amine)gives a positive carbylamine test, but dimethylamine does not.
(ii) Secondaryand tertiary amines can be distinguished by allowing them to react withHinsberg’s reagent (benzenesulphonyl chloride, C6H5SO2Cl).
Secondary amines react with Hinsberg’s reagent to form aproduct that is insoluble in an alkali. For example, N, N−diethylamine reactswith Hinsberg’s reagent to form N, N−diethylbenzenesulphonamide, which isinsoluble in an alkali. Tertiary amines, however, do not react with Hinsberg’sreagent.
(iii) Ethylamineand aniline can be distinguished using the azo-dye test. A dye is obtained whenaromatic amines react with HNO2 (NaNO2 +dil.HCl) at 0-5°C, followed by a reaction with the alkaline solution of2-naphthol. The dye is usually yellow, red, or orange in colour. Aliphaticamines give a brisk effervescence due (to the evolution of N2 gas)under similar conditions.
(iv) Anilineand benzylamine can be distinguished by their reactions with the help ofnitrous acid, which is prepared in situ from a mineral acid and sodium nitrite.Benzylamine reacts with nitrous acid to form unstable diazonium salt, which inturn gives alcohol with the evolution of nitrogen gas.
On the other hand, aniline reacts with HNO2 ata low temperature to form stable diazonium salt. Thus, nitrogen gas is notevolved.
(v) Anilineand N-methylaniline can be distinguished using the Carbylamine test. Primaryamines, on heating with chloroform and ethanolic potassium hydroxide, formfoul-smelling isocyanides or carbylamines. Aniline, being an aromatic primaryamine, gives positive carbylamine test. However, N-methylaniline, being asecondary amine does not.
