Tuning functional ionic deep eutectic solvents as green sorbents and catalysts for highly efficient capture and transformation of CO₂ to quinazoline-2,4(1H,3H)-dione and its derivatives

A series of functional ionic deep eutectic solvents (iDESs) containing pyridinolate anions were reported as green sorbents, solvents, and catalysts for highly efficient capture and transformation of CO2 to quinazoline-2,4 (1H,3H)-dione and its derivatives at mild conditions via tuning the structures of iDESs. Physical properties, such as density and viscosity, as well as flow activation energy and thermal expansion coefficient, were systematically investigated. Effects of the partial pressure of CO2 and the absorption temperature on the CO2 absorption capacity using these functional iDESs as sorbents were studied, and the different absorption mechanisms, including carbamate and carbonate pathways, were analyzed by FT-IR and 13C NMR spectroscopy. Additionally, thermodynamics analysis of CO2 absorption was performed according to the chemical reaction mechanism, and K-theta,Delta(r)G(theta)m),Delta(r)H(theta)m, and Delta(r)S(theta)mm were calculated. Furthermore, the effects of cations, anions, HBDs, reaction temperature, and the molar ratio of catalyst to substrate (nCat./nSub.) on CO2 conversion were systematically studied, and excellent isolated yield of up to 97.1% at mild conditions could be obtained with only 0.25 equiv. DES as the solvent as well as the sorbent and the catalyst. Plausible "simultaneous CO2 activation and substrate activation" reaction mechanism of capture and transformation of CO2 to quinazoline-2,4(1H,3H)-diones by [N2222][4-PyO]/DMSO (1:4) was verified by the spectra of FT-IR and based on previous reports. To the best of our knowledge, these are the first examples of tuning functional iDESs for the capture and transformation of CO2 to quinazoline-2,4-(1H,3H)-dione and its derivatives with only 0.25 equiv. DES. The method may also open a door to obtain the high efficiency of capture and transformation of such gases as NOx, SO2, CO, H2S, and CO2 by functional DESs.