A green catalysis of CO2 fixation to aliphatic cyclic carbonates by a new ionic liquid system

• An environmentally benign ionic liquid system for carbon dioxide fixation.
• Addition of carbon dioxide to non-polar aliphatic epoxides under mild reaction conditions.
• Relatively mild CO2 pressure and low temperature.
• Convenient recycling and reuse of the medium.

A mixed ionic liquid system has been developed for the efficient catalysis of CO2 addition to aliphatic epoxides without involving any transition metal catalysts or other additives. The ionic liquid integrated with pyridinium and pyrrolidinium groups (1·(Br)3) together with a non-polar ionic liquid (3·(Ntf)2) effectively transformed non-polar aliphatic epoxides to cyclic carbonates by the reaction with CO2 under mild CO2 pressure (3.0 MPa) and reaction temperature (80 °C). The presence of 3·(Ntf)2 remarkably improved the catalytic activity of 1·(Br)3 towards non-polar epoxides by increasing the miscibility of catalyst with the substrates. The mixed ionic liquid system is robust enough to be recycled without any significant loss of catalytic activity. GC–MS studies were performed to reveal the reaction pathways to the cyclic carbonates and a feasible model accounting for the effective CO2 activation in the ionic liquid system was proposed using density functional theory (DFT) calculations.

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