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) Gabriel phthalimide synthesis involves nucleophilic substitution (SN2) of alkyl halides by the anion formed by the phthalimide but aryl halides do not undergo nucleophilic substitution with the anion formed by the phthalimide and thus aromatic primary amines cannot be prepared by this process. (b) The reaction of a primary amine with benzene sulphonyl chloride gives a corresponding N-alkyl benzene sulphonylamide. Owing to the presence of a strong electron withdrawing sulphonyl group, attached to a nitrogen atom in N-alkyl benzene sulphonylamide, it is strongly acidic and dissolves in alkali. On the other hand, a reaction of the secondary amine with benzene sulphonyl chloride gives corresponding N,N-dialkyl benzene sulphonylamide which do not contain acidic hydrogen and hence is insoluble in alkali.