Mechanisms of ethylene glycol carbonylation with carbon dioxide

The direct synthesis of cyclic carbonate from polyol and CO2 is very attractive from both the environmental and carbon utilization points of view. In this work, the direct carbonylation of ethylene glycol and CO2 to ethylene carbonate without catalyst was investigated theoretically by quantum mechanical calculations. Two mechanisms, hydroxyl dehydration and carbonyl substitution, were proposed. Four reaction pathways and the corresponding transition states were identified and the corresponding energy profiles were calculated. All four reaction pathways contain the intramolecular cyclic process, which is the rate-determining step, and the energy barriers of the carbonyl substitution mechanism are lower than that of the hydroxyl dehydration mechanism. Solvent effects calculation indicates that the electrophilic attack of CO2 on the 1-hydroxyl group of ethylene glycol can be promoted by a polar solvent, but for other steps solvent effects are very limited.