Intramolecular nucleophilic cyclization of a carboxylic acid hydrazide under mild acid conditions

Phthaloyl-2′-nitrophenylhydrazide undergoes ring closure involving nucleophilic attack of the hydrazide on the carboxylic acid in dilute aqueous acid solution to form the corresponding N-substituted phthalimide. Structure of the resulting phthalimide was unequivocally confirmed by ¹³C-nmr.