Hydrogen Bond Donors Catalyzed CO₂ Cycloaddition Reaction To Epoxide

Carbon dioxide, one of the undesired greenhouse effect gases, is an abundant,inexpensive, and non-toxic renewable C1 resource, and so the development of a highly effective and environmental catalytic technology for CO₂ utilization by transforming into value-added products, can alleviate environment problem caused by global warming, and simultaneously bring enormous economic benefits.The combination of Bu4 NBr with co-catalyst CA was developed as novel homogeneous binary catalysts for the cycloaddition of carbon dioxide with epoxides yielding the corresponding cyclic carbonates. Various co-catalysts as well as the effects of reaction parameters（including reaction temperature, CO₂ pressure,Bu4NBr/CA molar ratio and reaction time） on catalytic activity for propylene carbonate（PC） synthesis from propylene oxide（PO） and CO₂ were investigated thoroughly. The results shown that at molar ratio 2:1 of Bu4NBr/CA, 97 % PC yield and 98% selectivity were obtained at 130 oC and 2.5 MPa for 4.0 h. Additionally, the catalysts life as well as the versatility towards epoxides with different substituents were investigated. Based on the results, the possible synergistic catalytic mechanism was proposed. The binary catalysts herein are simple, low cost, environmentally benign and highly efficient for CO₂ conversion, also the catalytic process avoid additional organic solvents and toxic transition metal ion participation.A series of triethanolamine protonated ionic liquids [TEA]X（X = Cl, Br, I） were synthesized and characterized by NMR and FTIR. The thermal stabilities were measured by TGA and EA. The catalytic performance of as-prepared [TEA]X ionic liquids were tested towards the model reaction of CO₂ cycloaddition to PO, and the reaction parameters（including reaction temperature, CO₂ pressure, catalyst loadings and reaction time） on catalytic activity were optimized. Among the catalysts, [TEA]I showed the best catalytic activity with 91% PC yield and 99% selectivity under solvent-free condition and 110 oC, 2.0 MPa for 6.0 h. The recycling experiments were tested by conducting the reaction at the optimized reaction conditions, there was no significant change of PC yield for three runs, and the recycled [TEA]I was essentially similar to its pristine form. Additionally, the versatile scopes of [TEA]I for the reactions of various epoxides with CO₂ were examined under the optimized reaction conditions, all exhibited outstanding catalytic activity. Finally, a possible synergistic catalytic mechanism was proposed. The developed one-component triethanolamine protonated ionic liquids showed the advantages of simple preparation, high catalyticactivity, mild reaction conditions, and avoiding the participation of co-catalyst and additional organic solvents, which make the catalyst show great development potential in the field of CO₂ catalytic conversion.