Question

Why 2 degree and 3 degree amine cant be formed by Gabriel Pthalimide synthesis?

Answer 1

Potassium Phthalimide is a -NH2-synthon which allows only the preparation of primary amines by reaction with alkyl halides. Alkyl halides reacts with the anion of the pthalimide under goes SN2 reaction to form primary amine. Hence we cannot prepare secondary amines and tertiary amines, further more tertiary amines cannot be prepared by the Gabriel synthesis because it would require that the nitrogen of phthalimide be alkylated with tert-butyl bromide by an SN2 reaction. Tertiary alkyl halides generally do not undergo SN2 reactions but, under basic conditions, undergo E2 reactions instead.