Boric acid as a hydrogen bond donor with TBAB catalyze the cycloaddition of CO2 to internal bio-epoxides under solvent-free conditions

Abstract

The cycloaddition of CO2 with epoxides is regarded as one of the most efficient methods to synthesize cyclic carbonate because of the 100% atom utilization. Therefore, it is necessary to develop efficient catalysts for the synthesis of cyclic carbonates. Hydrogen bond donors (HBDs) have been widely investigated due to their ability to activate epoxides and dramatically enhance the cycloaddition process. In this study, boric acid as a cheap HBD combined with TBAB as an effective co-catalysis system for cyclic carbonates synthesis through cycloaddition of CO2 to epoxidized soybean biodiesel. 92.3% yield of cyclic carbonates product was achieved at 100 °C with 10 bar pressure of CO2 for 10 h under solvent-free conditions. To further evaluate the catalyst activity, preliminary kinetic investigations were conducted and the results showed that activation energies (Ea) of cyclic carbonate formation were different (58.5 kJ/mol for TBAB, 44.22 kJ/mol for TBAB-boric acid). The results show that boric acid as HBD can efficiently improve the yield of cyclic carbonates. Thus, the developed catalyst system provides an efficient and economical approach for the industrial production of bio-based cyclic carbonates.