Synthesis of methyl cinnamate catalyzed by deep eutectic solvents based on choline chloride: kinetic studies

A series of green deep eutectic solvents (DESs: ChCl-PTSA, ChCl-2PTSA and ChCl-3PTSA) prepared by mixing choline chloride (ChCl) and p-toluenesulfonic acid monohydrate (PTSA) were applied to catalyze the esterification of methanol and cinnamic acid to synthesize methyl cinnamate. ChCl-3PTSA showed an excellent catalytic effect, hence it was adopted to explore the effects of agitation speed, catalyst loading, molar ratio of reactants and temperature on the conversion of cinnamic acid in detail. After that, the data obtained by kinetic experiments at 331.15–351.15 K were dynamically correlated by the activity-based pseudo-homogeneous (PH) model, and the kinetic parameters were compared with those obtained adopting p-toluenesulfonic acid and sodium bisulfate as catalysts. The relative deviations between the experimental values of cinnamic acid conversion catalyzed by ChCl-3PTSA and the calculated results by PH model are ~ 5%, which indicates that the model is applicable. Furthermore, the activity of ChCl-3PTSA did not decrease significantly after being conducted five cycles, indicating ChCl-3PTSA has the prospect of industrial application for the esterification reaction.