Synthesis of glycerol 1,2-carbonate by transesterification of glycerol with dimethyl carbonate using triethylamine as a facile separable homogeneous catalyst

The synthesis of glycerol 1,2-carbonate (GC) by transesterification of glycerol with dimethyl carbonate (DMC) using triethylamine (TEA) as a facile separable homogeneous catalyst has been studied at different temperatures, DMC/glycerol molar ratios and TEA/glycerol molar ratios. Reaction rate increases dramatically with temperature and TEA/glycerol molar ratio but the reaction is difficult to stop in the target molecule at the highest TEA/glycerol molar ratios because GC undergoes further transesterification to glycerol dicarbonate (GDC). However, good reaction control can be achieved by working at a TEA/glycerol molar ratio of 0.1: a 99% glycerol conversion and a 98% GC yield are obtained in 2.5 h with a DMC/glycerol molar ratio of 4 at refluxing temperature (88 degrees C -> 68 degrees C). At 90 degrees C glycidol is also formed in 6-10% yields. A mechanism to justify its synthesis is proposed. GDC formation can be avoided at conversions below 100% but in this case GC is highly impurified with glycerol after solvent removal by evaporation. To separate both chemicals a liquid-liquid extraction method has been developed. Selective extraction solvents for GC, such as methyl isobutyl ketone (MIBK) or DMC, were found using the method of miscibility numbers. GC is selectively extracted at room temperature in MIBK in a 100% yield with purity higher than 98% from a glycerol-GC mixture consisting of 80 wt% GC by using a MIBK/mixture mass ratio of 1.6 and three extraction steps.