Mechanism of the aminolysis of methyl benzoate: a computational study.

Density functional and ab initio methods were applied in examining the possible mechanistic pathways for the reaction of methyl benzoate with ammonia. Transition state structures and energies were determined for concerted and neutral stepwise mechanisms. The theoretical results show that the two possible pathways have similar activation energies. The general base catalysis of the process was also examined. The predictions reveal that the catalytic process results in considerable energy savings and the most favorable pathway of the reaction is through a general-base-catalyzed neutral stepwise mechanism. The structure and transition vectors of the transition states indicate that the catalytic role of ammonia is realized by facilitating the proton-transfer processes. Comparison of the energetics of the aminolysis for methyl benzoate and methyl formate shows the more favorable process to be that for the aliphatic ester. The differing reactivity of the two esters is explained in terms of the electrostatic potential values at the atoms of the ester functionality.