Protonated triethanolamine as multi-hydrogen bond donors catalyst for efficient cycloaddition of CO2 to epoxides under mild and cocatalyst-free conditions

Abstract

The protonated triethanolamine salts with multiple hydrogen bond donor groups were one-step prepared and demonstrated to be simple, environmentally benign and highly efficient catalyst for the chemical fixation of carbon dioxide to cyclic carbonates under mild reaction conditions without additional cocatalyst and organic solvent participation. Hydrogen-bonding activation towards epoxide is a special class of mimetic alternative to Lewis acid activation for favor of opening the epoxy ring, which was recognized as the rate-determining step for the CO2 cycloaddition reaction. Here the effects of reaction parameters on catalytic activity for propylene carbonate (PC) synthesis from propylene oxide (PO) and CO2 were investigated thoroughly. With 0.65mmol (1.88 mol%) catalyst loading, 91% PC yield with 99% selectivity were obtained at 110°C and 2.0MPa for 6.0h. The [HTEA]I catalyst could be easily separated and regenerated from the reaction products for subsequent reuse, also displayed versatility to CO2 cycloaddition with other epoxides. Additionally, the possible synergistic catalytic mechanism deriving from cation and anion of protonated triethanolamine catalyst was proposed.