KINETIC EVIDENCE FOR THE OCCURRENCE OF A STEPWISE MECHANISM IN HYDRAZINOLYSIS OF PHTHALIMIDE

The apparent second-order rate constants, k(napp), for the reaction of hydrazine with phthalimide at a constant pH follow the empirical relationship k(napp) = A(1)[Am](T)/(1 + A(2)[Am](T)), where [Am](T) represents the total hydrazine buffer concentration. The nonlinear variation of k(napp) against [Am](T) is attributed to the change in the rate-determining step with change in [Am](T) at a constant pH, and this provides evidence for the existence of an intermediate on the reaction path. The cyclization of o-(aminocarbamoyl)benzamide to 2,3-dihydrophthalazine-1,4-dione involves N-aminophthalimide as the intermediate.