Account for the following:

a. Gabriel phthalimide synthesis is not preferred for preparing aromatic primary amines.

b. On reaction with benzene sulphonyl chloride, primary amine yields product soluble in alkali whereas secondary amine yields product insoluble in alkali.

a. Aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis method because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

b. The reaction of benzene sulphonyl chloride with primary amine yields N-ethyl benzene sulphonyl amide. The hydrogen attached to nitrogen in sulphonamide is strongly acidic due to the presence of strong electron withdrawing sulphonyl group. Hence, it is soluble in alkali.

In the reaction with secondary amine, N,N-diethyl benzene sulphonamide is formed. Since N, N-diethyl benzene sulphonamide does not contain any hydrogen atom attached to nitrogen atom, it is not acidic and hence insoluble in alkali.