Synthesis of cyclic carbonates from CO2 and propylene oxide (PO) with deep eutectic solvents (DESs) based on amino acids (AAs) and dicarboxylic acids

A novel synthesis of cyclic carbonates from CO2 and PO with DESs, based on AAs and dicarboxylic acids, was developed. The eutectic mixture of L-proline (L-Pro)/propanedioic acid (PA) system exhibited high activity and selectivity for cycloaddition of carbon dioxide to PO among the prepared DESs. The influencing parameters (reaction temperature, CO2 pressure and time) on yield and selectivity of propylene carbonate (PC) was investigated and optimized. The PC yield of the L-Pro/PA system can reach as high as 98% under optimal conditions. Furthermore, the L-Pro/PA system was readily recovered and reused over 9 times without noticeable decrease in yield and selectivity of PC. The synergistic effect of bromide anion, the AAs and the dicarboxylic acids is perhaps the main reason for the high catalytic activity. In addition, the lengths of carbon chain of dicarboxylic acids play a complicated role in the cycloaddition of CO2 to PO with DESs based AAs and dicarboxylic acids, which may be related hydrogen bond strength.