Chemical fixation of CO2 with propylene oxide catalyzed by Trimethylsulfonium bromide in the presence of HBr: a computational study

The chemical fixation of CO(2)into value-added chemicals has recently received much attention with regard to the utilization of CO2, a gas responsible for global warming. One of the most well-known methods is the fixation of CO2 with epoxides to form cyclic carbonates. In this work, the conversion of CO(2)and PO into five-membered cyclic carbonate catalyzed by (CH3)(3)SBr alone and (CH3)(3)SBr in the presence of HBr have been studied by using DFT method at B3LYP/6-311 ++ G (d, p)//B3LYP/6-31G (d) level of theory to understand the reaction mechanism and efficiency of the catalyst. Two possible reaction mechanisms (alpha and beta) were considered and it was found that the beta pathway is more favorable over alpha pathway for the catalyzed route in gas phase. The ring-opening step was the rate-determining step that results from the nucleophilic attack of the bromide to the carbon atom of the epoxide. The synergetic effect of HBr is tested as HBD for the (CH3)(3)SBr/HBr catalyzed reaction and it gave better result and minimized the activation energy for the reaction and the rate-determining step was the ring closure with free energy of activation 5.2 kcal/mol in gas phase.