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 CO 2 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 CO 2 with propylene oxide (PO) to propylene carbonate (PC). Density functional theory (DFT) was used to calculate the catalytic performance of DES in CO 2 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 CO 2 , 90 °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 CO 2 , 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 CO 2 and epoxides. The synergistic catalytic effect of the double hydrogen bonds between DES and Br anions is the reason for its high efficiency. © 2023 Society of Chemical Industry.