Reaction Mechanisms and Kinetics of the Melt Transesterification of Bisphenol-A and Diphenyl Carbonate

摘要

The catalyzed and uncatalyzed reaction mechanisms of the melt transesterification process of bisphenol-A and diphenyl carbonate are proposed based on nucleophilic substitution at the carbonyl group of the reactants. The reaction paths and energy barriers of the melt transesterification reaction were predicted and identified via density functional theory (DFT) calculations. The calculations reveal that the different oligomers with only one repeating unit are formed through different thermal processes. The theoretical evaluation further indicates that the basic hydroxide catalysts can reduce the energy barrier for the transesterification reaction, which allows subsequent nucleophilic attack to easily occur. Furthermore, the reaction kinetics of transesterification using tetraethyl ammonium hydroxide as a catalyst were investigated experimentally over a temperature range of 155-175 degrees C. The reaction rate constants and equilibrium constants were determined based on the functional group model, and the equilibrium constants decreased with increasing reaction temperature. A detailed molecular species model with a specific repeating unit (n = 3) was developed and applied to predict the change in the reactants, oligomers, and phenol, and the experimental data and model calculation agree quite well. The standard curves of the oligomer were reversely derived, which provide intuitive insight into the concentration change of each oligomer. Both the DFT calculations and experimental results indicate that the C1 oligomer is first formed, and some of which are then converted to other types or higher molecular weight oligomers. (C) 2018 Wiley Periodicals, Inc.