Catalytic effect of different hydroxyl-functionalised ionic liquids together with Zn(II) complex in the synthesis of cyclic carbonates from CO2

Abstract Quaternary ammonium salts bearing different alkyl chains and hydroxyl groups were synthesized and tested for the first time as co-catalysts in the cycloaddition reaction between CO2 and propylene oxide. Their synergetic catalytic effect together with the known tetranuclear zinc(II) complex [Zn4(μ3-OH)2 (1κO:2κO-HL)4(κO-HL)2(H2O)4] (1), H2L = 3-(2-carboxyphenyl-hydrazone)pentane-2,4-dione, was investigated at 60 °C and 4 MPa. Results obtained highlight the importance of exploring the hydrogen bonding effect via functionalization with hydroxyl groups but show that the length of the alkyl chains of the ammonium cation is a more relevant factor affecting the reaction kinetic for the system studied.