Novel biomass-derived deep eutectic solvents promoted cycloaddition of CO2 with epoxides under mild and additive-free conditions

Chemical fixation of CO 2 to produce high value-added chemicals is one of the important measures to effectively control carbon emission. In this paper, novel biomass-derived deep eutectic solvents (BDESs) with multiple active sites were developed as green media for chemical conversion of CO 2 and epoxides into cyclic carbonates . The coupling of propylene oxide (PO) and CO 2 was selected as a model reaction to evaluate the catalytic activity. By screening various BDESs structures and reaction parameters, the iodide choline/citric acid (ChI/CA) with a molar ratio of 2:1 was proved to be an efficient catalytic medium, and it could afford 98 % propylene carbonate (PC) yield with 99 % selectivity under mild (70 °C, 0.5 MPa, 3 h) and additive-free conditions. Moreover, the catalyst reusability and versatility were examined. The ChI/CA could be reused in up to five consecutive runs without loss of activity, and the ChI/CA showed excellent activity to various terminal epoxides/CO 2 coupling reaction. Finally, the activation behaviors of the ChI/CA to the CO 2 and epoxide were studied respectively, and a synergistic catalytic mechanism was provided.