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 CO2 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 degrees 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. (C) 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.