The synthesis of glycerol carbonate from glycerol and urea using deep eutectic solvent ZnCl2:Acetamide as a catalyst

A series of deep eutectic solvents (DESs) with ZnCl2 as hydrogen bonding acceptor and monoethanolamine (MEA) or acetamide as hydrogen bonding donor were prepared and used as catalysts for the reaction of glycerol and urea to synthesize glycerol carbonate (GC) without any additional organic solvent and co-catalyst. FT-IR, TGA, DSC and pH value were used to characterize the physicochemical properties of the prepared DESs. The effect of reaction temperature, urea to glycerol molar ratio, catalyst amount, and reaction time on the reaction were further investigated. The results show that ZnCl2:Acetamide (1:2) DES possess the highest catalytic activity because of the strong hydrogen bond network between ZnCl2 and acetamide and the hydrogen bonding interactions between ZnCl2:Acetamide (1:2) and reactants, which were shown by FTIR spectra. The glycerol conversion of 93.85 % and GC yield of 90.77 % were obtained at reaction temperature of 140 degrees C, urea to GL molar ratio of 1:1, catalyst amount of 5 wt% (based on the GL weight) and reaction time of 2 h. Based on the experimental results and characterization by FTIR and ESI-MS, the reaction mechanism was proposed.