High-performance and selective catalyst for the chemical fixation of CO2 into cyclic carbonates based on pyridinium-based deep eutectic solvent

Rising atmospheric CO2 levels have prompted interest in chemical fixation routes to convert CO2 into value-added cyclic carbonates. This study reports a high-performance catalyst based on a pyridinium-based deep eutectic solvent (DES) for CO2 cycloaddition with epoxides under mild conditions. The DES was prepared by mixing 1-(carboxymethyl)pyridinium bromide ([CMPy]Br) as a hydrogen bond acceptor with maleic acid as an inexpensive and eco-friendly hydrogen bond donor [HBD]. The melting point depression enables the DES to act as a homogeneous catalyst without additional solvents. A diverse range of cyclic carbonates were synthesized in high yields from various epoxides and CO2 under atmospheric pressure at 90-110°C temperatures. Compared to other catalytic systems, the offered DES significantly reduced reaction times of 1-3 hours to achieve best quantitative conversions. The DES was recyclable for at least 5 runs without loss of activity. The high performance was attributed to the DES' ability to activate epoxides via hydrogen bonding while stabilizing reaction intermediates. This metal-free and solvent-free approach provides an efficient strategy for CO2 utilization under green conditions using readily available pyridinium-based DES.