Theoretical Studies on the Aminolysis Mechanism of Methomyl: Effect of the Catalysis to the Reaction of Carbamate with Ammonia

Abstract

AbstractThe aminolysis mechanisms of methomyl are systematically investigated through the M06‐2X/6‐311++G(d,p) and MP2/6‐311+G(d,p) methods. The uncatalyzed, base‐catalyzed and water‐catalyzed aminolysis processes are also taken into consideration together with the concerted, BAC2 (a stepwise channel through a neutral tetrahedral intermediate) and E1cB (a stepwise mechanism via an isocyanate intermediate) pathways. The solvent effects are discussed in detail by using the CPCM (conductor‐like polarized continuum model) with the M06‐2X/6‐311++G(d,p) method. The computational values provide convincing evidence that three alternative pathways possess similar energy barriers for the uncatalyzed aminolysis. It can be concluded that the base‐catalyzed and water‐catalyzed aminolysis processes are more favorable compared with the uncatalyzed reaction. Concerning the base‐catalyzed process, the E1cB pathway is preferable to other channels. However, the water‐catalyzed aminolysis is dominated by the BAC2 mechanism. In a word, the aminolysis reactions in solution could readily occur and the solvent effects do not remarkably alter the mechanism.