Synthesis of glycerol carbonate from 3-chloro-1,2-propanediol and carbon dioxide using triethylamine as both solvent and CO₂ fixation-activation agent

The synthesis of glycerol carbonate from 3-chloro-1,2-propanediol, a glycerol derivative easily obtained by reacting glycerol with HCl, and carbon dioxide using triethylamine as both solvent and CO₂ fixation and activation agent is reported. The influence on conversions and yields of triethylamine/3-chloro-1,2-propanediol molar ratio, temperature, CO₂ pressure and reaction time has been studied. A 3-chloro-1,2-propanediol conversion of 100% and a glycerol carbonate yield of 90% are obtained at 100°C, using a triethylamine/3-chloro-1,2-propanediol molar ratio of 1.5, a carbon dioxide pressure of 25bar and 60min. Glycerol was the only byproduct detected in 4-6% yields independently of experimental conditions. Above 100°C, glycerol carbonate yield decreases dramatically due to glycerol carbonate polymerization resulting in a polyglycerol mixture. The yield of glycerol carbonate is strongly and negatively influenced by the presence of water. A reaction mechanism is proposed in which the first step is the formation of a zwitterionic adduct between triethylamine and CO₂ which reacts with 3-chloro-1,2-propanediol leading to an intermediate which evolves towards glycerol carbonate either directly or through the glycidol intermediate.