DFT study of the acid-catalyzed ethanolysis of butyric acid monoglyceride: Solvent effects

The reaction mechanism of the acid-catalyzed transesterification of butyric acid monoglyceride was studied employing Density Functional Theory (DFT). Solvent effects were included by means of the integral equation formalism for the polarizable continuum model (IEFPCM). It was found that both in the gas phase and in solution the reaction proceeds through a concerted mechanism with a single transition state (TS) and without the formation of a tetrahedral intermediate. The inclusion of micro-solvation to model the transesterification reaction led to a stepwise mechanism where the rate determining step is the decomposition of the intermediate adduct and the formation of the tetrahedral intermediate has a lower energy barrier. The structure of the intermediate is stabilized by the formation of two rings making the glycerol backbone more rigid and contributing to stabilizing the tetrahedral intermediate by lowering the total energy of the system due to its intrinsic H bonds.