Tetrabutylammonium bromide/triethanolamine deep eutectic solvents with double hydrogen bond as efficient catalysts for fixation of CO2 in cyclic carbonates under mild conditions

BACKGROUND: Carbon dioxide is not only a major greenhouse gas but also an important carbon resource, which is abundant, renewable, low cost and non-toxic. The coupling reaction of CO2 with epoxides has shown great potential in the field of chemical carbon fixation due to its 100% atomic utilization efficiency. Deep eutectic solvents (DESs) based on tetrabutylammonium bromide (TBAB) were evaluated for cycloaddition reaction of CO2 with propylene oxide (PO) to propylene carbonate (PC). Density functional theory (DFT) was used to calculate the catalytic performance of DES in CO2 cycloaddition reaction. RESULTS: The utilization of DES containing triethanolamine (TEA) as hydrogen bond donor significantly shortened the reaction time. Under optimal reaction conditions (30 mmol PO, 5 mol% TBAB/TEA (1:1) DES, 1.0 MPa CO2, 90 degrees C, 2 h), high PC yield (98%) was obtained. DFT calculations revealed that TBAB/TEA (1:1) DES was used as the catalyst for the coupling reaction between PO and CO2, with the ring-opening process serving as the rate-determining step and energy barrier of 17.9 kcal mol(-1). TBAB/TEA (1:1) DES exhibited excellent recyclability and could be reused more than five times. CONCLUSION: TBAB/TEA (1:1) DES is a highly efficient homogeneous catalyst for the synthesis of cyclic carbonates through the cycloaddition reaction of CO2 and epoxides. The synergistic catalytic effect of the double hydrogen bonds between DES and Br anions is the reason for its high efficiency. (c) 2023 Society of Chemical Industry.