Influence of acidic strength on the catalytic activity of Brønsted acidic ionic liquids on synthesizing cyclic carbonate from carbon dioxide and epoxide

• Brønsted acidic ionic liquid is a highly effective catalyst for synthesizing cyclic carbonate.
• The acidic strength of Brønsted acidic ionic liquids affect its catalytic activity.
• Brønsted acidic ionic liquids with excellent stability and recyclability.
• The synergistic effects of cation and anion in Brønsted acidic ionic liquids.

The chemical fixation of CO2 with epoxides to form cyclic carbonates was carried out with excellent selectivity and yield in the presence of Brønsted acidic ionic liquids without using additional organic solvents and co-catalyst. The acidic strength of ionic liquids was determined and its effect on the synthesis of cyclic carbonates was investigated. The reaction conditions (temperature, CO2 pressure and reaction time) were optimized, and the Brønsted acidic ionic liquids showed highly catalytic activity under the optimal reaction conditions. A plausible reaction mechanism was suggested and it was demonstrated that the carboxylic group in Brønsted acidic ionic liquids had synergetic effect with halide. Moreover, the catalyst could be used five times without significant decrease in its catalytic activity.

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