Theoretical Study of the Reaction of Succinic Anhydride with Benzocaine

The density functional theory (ωB97M-V/ma-def2-QZVPP//r2SCAN-3c level) is used to study possible concerted and two-stage reaction pathways for aminolysis of succinic anhydride by benzocaine. Three variants are considered for each mechanism: without catalysis, self-catalysis by a reagent molecule (benzocaine), and autocatalysis by a product (succinamide). Thermodynamic and activation parameters of all elementary stages in the gas phase are calculated. It is shown that different mechanisms participate in the reaction: in the early stages, pathways of both concerted and two-stage self-catalysis can be obtained with equal probability; as the product forms, stepwise autocatalysis with a limiting first stage becomes the preferred route of the reaction.