Choline-based eutectic mixtures as catalysts for effective synthesis of cyclic carbonates from epoxides and CO2

Abstract

CO2 is a renewable, abundant and cheap C1-feedstock and its conversion to cyclic carbonates starting from epoxides has been widely explored in the last years. Nevertheless, conducting this reaction under mild and sustainable conditions is still a challenging task. Herein we present the use of choline-salt based eutectic mixtures as catalysts for the reaction of CO2 with epoxides to give cyclic carbonates. Choline chloride and choline iodide have been coupled with various hydrogen bond donors (HBDs), mainly cheap and bio-based carboxylic acids and polyols, to form two classes of eutectic mixtures. Very good yields were achieved under mild conditions (80 °C in 7–22 h) for various terminal epoxides, with both classes of catalysts. While a pressure of 0.4 MPa of CO2 is required to obtain appreciable conversions using choline chloride-based mixture, atmospheric pressure of CO2 (balloon) has been successfully used with choline iodide-based mixtures. Furthermore, the catalysts could be recycled without appreciable loss of the catalytic activity. The improved catalytic performance of both choline-based eutectic mixtures is attributed to the synergistic activity of the halide, responsible for the opening of the epoxy-ring, and the HBD that has a role in the stabilization of the alkoxide intermediate.