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

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 CO ₂ 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.