Reusable and efficient polymer-supported task-specific ionic liquid catalyst for cycloaddition of epoxide with CO₂

1-(2-Hydroxyl-ethyl)-imidazolium-based ionic liquids (HEIMX, X = Cl, Br, I), which have both acidic and basic characteristics, were covalently anchored onto a highly cross-linked polystyrene resin. The catalytic activity of these heterogeneous catalysts for the synthesis of cyclic carbonates via cycloaddition reaction of CO₂ with epoxides was studied. The effects of parameters, such as anions of the catalysts, reaction temperature, pressure, reaction time, and the amount of catalyst used, on the reaction were also investigated. It was demonstrated that the hydroxyl group in the catalyst had synergetic effect with the halide anion. As a result, high yield (80-99%) and excellent selectivity (92-99%) of cyclic carbonates could be achieved at mild conditions (2.5 MPa, 120 °C and 4 h) without any co-solvent. In addition, the catalyst recycle test showed that the supported catalyst could be reused for as many as six times without loss of catalytic activity.