Question

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

Answer 1

Hinsberg's method: Benzenesulphonyl chloride (C₆H₅SO₂Cl) (known as Hinsberg’s reagent) reacts with primary and secondary amines to form sulphonamides. The method is used for the distinction of primary, secondary and tertiary amines.

Sulphonamide formed in case of a primary (1°) amine is soluble in an alkali.

\[{C_6 H_5 - SOCl}_{Benzenamine} + {C_2 H_5 - {NH}_2}_{Acetyl chloride} \to^{} {C_6 H_5 - SO - NH - C_2 H_5}_{N - Phenylethanamide} + HCl\]

Sulphonamide formed in case of a secondary (2°) amine remains insoluble in an alkali.

\[C_6 H_5 - {SO}_2 Cl + NH \left( C_2 H_5 \right)_2 \to {{C_6 H_5 - {SO}_2 - N \left( C_2 H_5 \right)_2}_{N, N - Diethylbenzenesulphonamide}}_\left( Insoluble in alkali \right) + HCl\]

A tertiary (3°) amine does not give a positive Hinsberg test.