The kinetics of nucleophilic cleavage of maleimide have been studied at 30 "C under the buffer solutions of 13 primary amines including three diamines and carbonate. Both ionized ( S -) and non-ionized (SH) forms of maleimide have been found to exhibit significant reactivity toward amines and carbonate anion. The respective bimolecular rate constants k, and k, for the reactions of nucleophiles with non-ionized and ionized forms of maleimide display Bronsted plots with respective slopes of pnuc, = 0.81 f 0.1 5 and pnuc, = 0.48 f 0.19. The significantly different values of pnuc, and pnuc, reveal the involvement of different rate-determining steps in the nucleophilic cleavage of non-ionized and ionized maleimide. The high value of pnuc, is attributed to the expulsion of the leaving group as the rate-determining step while the value of pnuc, of 0.48 indicates the nucleophilic attack within the encounter complex as the ratedetermining step. The values of pnuc, and pnuc, for the nucleophilic reactivity of diamines were found to be 0.52 f 0.02 and 0.13 f 0.02, respectively. The value of pnuc, of 0.52 has been attributed to intramolecular general acid-base-catalysed expulsion of the leaving group as the rate-determining step. The l o w value of pnuc, (0.13) reveals the nucleophilic attack as the rate-determining step. A preassociation stepwise mechanism is proposed for the reactions of amines with Swhile a diffusioncontrolled trapping mechanism is favoured for the reactions of amines with SH. The rate constants k, and k, for TRIS, 2-amino-2-methylpropane-1,3-diol, ammonia, and carbonate have been found to show significant negative deviations while hydrazine revealed a large positive deviation from Bronsted plots.