Aminolysis of a model carbamate insecticide: a theoretical reaction mechanism study of carbaryl via an isocyanate intermediate

The possible aminolysis pathways of carbaryl are investigated by using the B3LYP/6-311++G(d,p), M06-2X/6-311++G(d,p) and MP2/6-311++G(d,p) levels. The uncatalyzed, base-catalyzed and water-catalyzed aminolyses are explored in our calculation. For each case, three alterative channels, the concerted, addition–elimination (BAC2) and elimination–addition (E1cB) channel via an isocyanate, are evaluated. Our results convincingly demonstrate that the most favorable mechanism is the E1cB channel for all of the aminolysis reactions in the gas phase. For BAC2 and E1cB routes, the first stage is the rate-determining step. The base-catalyzed and water-catalyzed aminolysis reactions have more advantages to the uncatalyzed one. The solvent effect for acetonitrile does not notably alter the mechanism of the aminolysis.