Chemical fixation of CO 2 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 CO 2 , a gas responsible for global warming. One of the most well-known methods is the fixation of CO 2 with epoxides to form cyclic carbonates. In this work, the conversion of CO 2 and PO into five-membered cyclic carbonate catalyzed by (CH 3 ) 3 SBr alone and (CH 3 ) 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 ( α and β ) were considered and it was found that the β pathway is more favorable over α 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 (CH 3 ) 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.