Protic Pyrazolium Ionic Liquids: An Efficient Catalyst for Conversion of CO2 in the Absence of Metal and Solvent

A series of novel protic pyrazolium ionic liquids are first synthesized and utilized as catalysts for cycloaddition of carbon dioxide and epoxides to form cyclic carbonates under metal- and solvent-free conditions. The new developed protic pyrazolium ionic liquids present excellent catalytic activity toward the fixation of carbon dioxide. More importantly, they would be prepared by a facile two-step reaction from cheap raw starting materials with a yield more than 90%. The influence of catalyst dosage, reaction temperature, carbon dioxide pressure, and reaction time on the synthesis of cyclic carbonates is investigated to identify the optimal reaction conditions. Under the optimum conditions, the catalyst suitability is studied. Additionally, the possible reaction mechanism is investigated by the double-IL model to elucidate the synergistic effects of electrostatic and weak interaction in the catalytic process.