Describe the method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reaction involved.

Primary amine: A primary (1°) amine is an amine that has the following general structural formula.

R= alkyl or aryl group

Secondary amine: A secondary (2°) amine is an amine that has the following general structural formula.

R¹ and R²= alkyl or aryl group

Tertiary amine: A tertiary amine is an amine that has the following structure

R¹, R² and R³ are alkyl or aryl groups

Identification of Primary, Secondary and Tertiary amines

Primary, secondary and tertiary amines can be identified by the following test:

Hinsberg’s test: This is an excellent test for the identification of primary, secondary and tertiary amines. In this test, the amine is shaken with benzenesulphonyl chloride ( Hinsberg’s reagent) in the presence of an excess of aqueous KOH solution when

(i) A primary amine gives a clear solution which on acidification gives an N-alkylbenzene sulphonamide which is soluble in alkali.

Due to the presence of strong electron withdrawing sulphonyl group in the sulphonamide, the H-atom attached to nitrogen can be easily released as a proton. So it is acidic and dissolves in alkali.

(ii) A secondary amine reacts with Hinsberg's reagent to give a sulphonamide which is soluble in water.

There is no H-atom attached to the N-atom in the sulphonamide Therefore it is not acidic and soluble in alkali.

(iii) A Tertiary amine does not react with Hinsberg’s reagent at all