Influence of different substitution in pyrazolium ionic liquids on catalytic activity for the fixation of CO2 under solvent- and metal-free conditions.

Three pyrazolium ionic liquids, 1,2-diethylpyrazolium bromide (DEPzBr), 1,2-diethyl-3-methylpyrazolium bromide (DEMPzBr), and 1,2-diethyl-3,5-dimethylpyrazolium bromide (DEDMPzBr), are firstly applied as catalysts for coupling reaction of carbon dioxide (CO 2 ) and propylene oxide (PO) with the propylene carbonate (PC) yields in a range of 82.7%–88.7% under a benign condition, 120 °C, 2.0 MPa initial CO 2 pressure and 4 h with 0.5 mol% catalysts loading. The relationship between structure and catalytic activity of pyrazolium ionic liquids are investigated by two different theoretical models, which indicates that both electrostatic interaction and hydrogen bond promote the ring-opening of PO. Both the theoretical and experimental results present that the catalytic activity decreases in the sequence of DEPzBr > DEDMPzBr > DEMPzBr. Pyrazolium ionic liquids would be employed as a novel efficient single-component catalyst without solvent and co-catalyst. It is expected that we would open an express pathway to develop new catalysts with the desired properties. [ABSTRACT FROM AUTHOR]