A DFT investigation of methanolysis and hydrolysis of triacetin

TL;DR

This study uses DFT calculations to analyze the thermodynamics and kinetics of methanolysis and hydrolysis of triacetin, revealing mechanisms and factors influencing reaction pathways relevant to biodiesel production.

Contribution

It presents the first proposed mechanism for acid-catalyzed methanolysis of esters and examines effects of various factors on reaction energetics using DFT.

Findings

Reaction mechanisms align with experimental biodiesel data

Middle position of glycerol is most reactive, confirmed by NMR

Activation energies match observed reaction trends

Abstract

The thermodynamic and kinetic aspects of the methanolysis and hydrolysis reactions of glycerol triacetate or triacetin, a model triacylglycerol compound, were investigated by using Density Functional Theory (DFT) at the B3LYP/6-31++G(d,p) level of calculation. Twelve elementary steps of triacetin methanolysis were studied under acid-catalyzed and base-catalyzed conditions. The mechanism of acid-catalyzed methanolysis reaction which has not been reported yet for any esters was proposed. The effects of substitution, methanolysis/hydrolysis position, solvent and face of nucleophilic attack on the free energy of reaction and activation energy were examined. The prediction confirmed the facile position at the middle position of glycerol observed by NMR techniques. The calculated activation energy and the trends of those factors agree with existing experimental observations in biodiesel production.