Proton exchange and transesterification reactions of acetate enolates with alcohols in the gas phase

Transesterification reactions and proton exchange reactions between acetate enolates and alcohols were studied both separately and together. Kinetic analysis shows that transesterification and proton exchange happen in a single collision event. The transesterification reaction is best viewed as an endothermic proton transfer, followed by an exchange of alkoxide and an exothermic proton transfer. Reaction barriers were modeled by Rice-Ramsperger-Kassel-Marcus theory and compared to quantum calculations. CBS-QB3 achieves good agreement whereas B3LYP and MP2 give slightly higher barriers. Quantum calculations also predict that the transition state for these transesterification reactions is the same as that for direct transesterification reactions between alkoxides and esters.