Temperature-responsive self-separation ionic liquid system of zwitterionic-type quaternary ammonium-KI for CO2 fixation

A series of zwitterionic-type quaternary ammoniums (ZTQAs) with varying lengths of alkyl chains combined with KI were synthesized and considered as catalysts for the coupling reaction of CO 2 and various terminal epoxides. The prolonged alkyl chain of ZTQAs exhibited temperature-responsive self-separation in propylene carbonate (PC). The interaction between ZTQAs and KI was confirmed by X-ray photoelectron spectroscopy and quantum chemical calculations. This interaction strengthened the nucleophilicity of the I − ion, favoring the catalytic reaction . The 3-(dimethyltetradecylammonium) propane sulfonate (DTPS)/KI showed an excellent yield of PC (95.1%) at 125 °C, 1.5 MPa, and 1 mol% loading of catalyst. The precipitate formed spontaneously from the catalytic system, providing high catalytic activity of the homogeneous catalyst, as well as easy recovery of the heterogeneous catalyst.