Explain with equations how methylamine, N, N - dimethylamine and N, N, N - trimethylamine react with benzenesulphonyl chloride and how this reaction is useful to separate these amines.

Explanation

Benzene sulphonyl chloride is called Hinsberg's reagent. This is used to distinguish the `1^(@),2^(@),3^(@)` - amines.
`to` with `1^(@)` - amine : Benzene sulphonyl chloride reacts with `1^(@)` - amine and produce N - Alkyl benzene sulphonamide which is soluble in alkali.

`to` with `2^(@)` - amine : Benzene sulphonyl chloride reacts with `2^(@)` - amine and produce N, N - Dialkyl benzene sulphonamide which is insoluble in alkali

`to` with `3^(@)` - amine : Benzene sulphonyl chloride does not react with benzene sulphonyl chloride.