Reaction Pathways and Energy Barriers for Alkaline Hydrolysis of Carboxylic Acid Esters in Water Studied by a Hybrid Supermolecule-Polarizable Continuum Approach

Abstract

Reaction pathways, solvent effects, and energy barriers have been determined for the base-catalyzed hydrolysis of two representative alkyl esters in aqueous solution, using a hybrid supermolecule-polarizable continuum approach. Four solvent water molecules were explicitly included in the supermolecular reaction coordinate calculations; the remaining solvent water was modeled as a polarizable dielectric continuum surrounding the supermolecular reaction system. Two competing reaction pathways were observed, sharing a common first step, i.e. the formation of the tetrahedral intermediate. One pathway involves a direct proton transfer in the second step, i.e. the decomposition of the tetrahedral intermediate. A second pathway involves a water-assisted proton transfer during the decomposition of the tetrahedral intermediate. The direct participation of the solvent water molecule in the proton-transfer process significantly drops the energy barrier for the decomposition of the tetrahedral intermediate. Thus, the...