Novel hydroxyl-functionalized ionic liquids as efficient catalysts for the conversion of CO2 into cyclic carbonates under metal/halogen/cocatalyst/solvent-free conditions

Abstract

The development of sustainable catalysts for the conversion of carbon dioxide into value-added chemicals is an effective way to alleviate environmental problems. The design of catalysts with excellent catalytic activities that are able to efficiently convert CO₂ under mild conditions is very important. The novel, single-component, metal-free functionalized ionic liquids ([N_2,2,2,2OH][BA], [N_2,2,2,2OH][SA], [N_2,2,2,2OH][OAc], [N_2,2,2,2OH][GA], [N_2,2,2,2][BA]) were synthesized using a simple method, and were further used as efficient catalysts for the catalytic conversion of CO₂ into cyclic carbonates without any solvent and co-catalyst. These ionic liquids exhibited outstanding catalytic activity for the conversion of CO₂ and various epoxides to cyclic carbonates. A mechanism for the synergistic effects of cations and anions in functionalized ionic liquids was also proposed. The catalytic activity of [N_2,2,2,2][BA] without any OH functional groups was clearly lower than that of [N_2,2,2,2OH][BA]. The relationship between the higher catalytic reactivity and the OH functional group presence was shown.