On the chemical fixation of supercritical carbon dioxide with epoxides catalyzed by ionic salts: an in situ FTIR and Raman study

A series of ionic salts have been investigated to catalyze the coupling reaction between epoxide and carbon dioxide at T = 80 °C and P = 8 MPa. Among them, we focused particularly on tetrabutylammonium, imidazolium and guanidinium salts. The kinetics of the synthesis was monitored in situ using both FTIR and Raman spectroscopy. For a given reaction time, the best yields were obtained with 1,5,7-triaza-bicyclo[4.4.0]dec-5-enium bromide (TBD·HBr) and 1-methyl-3-methylimidazolium iodide (MMImI) and both have not been investigated in detail in the literature before. Thanks to this catalyst screening, we have verified how some functional groups of the catalyst can activate the epoxide and the CO2 molecule enabling us to go further in the mechanism comprehension of this reaction. Due to its easier and less expensive synthesis than other ionic liquids, we focused more particularly on TBD·HBr that also offers a good conversion rate even at low pressure (80 °C and 1 MPa).