Catalytic Conversion of CO2 from Simulated Flue Gases with Aminophenol-Based Protic Ionic Liquids to Produce Quinazoline-2,4(1H,3H)-diones under Mild Conditions

Novel aminophenol-based protic ionic liquids (APILs) were designed and synthesized via one-step neutralization, and they were used as catalysts for conversion of 2-aminobenzonitriles and CO2 from simulated flue gases to produce quinazoline-2,4(1H,3H)-diones under mild conditions. The effects of anion–cation structures of APILs, various solvents, reaction parameters, and water contents on the product yields were investigated in detail. The catalyst recyclability and general applicability to different substrates were examined. It showed that both the basicity of the reaction media and the synergistic activation of zwitterions to reactants played important roles during the catalysis. The optimum [HTMG][m-AP] catalyst cooperating with the dimethylformamide (DMF) solvent could selectively convert CO2 into various quinazoline-2,4(1H,3H)-diones with good to excellent product yields at 60 °C and in a 0.1 MPa simulated flue gas atmosphere. In addition, [HTMG][m-AP]/DMF was easily recycled and could be reused in up to five consecutive cycles without an obvious loss of activity. By comparison with the reported catalysts, [HTMG][m-AP]/DMF here showed a superior catalytic performance and a great potential for development. Finally, the activation behaviors of [HTMG][m-AP]/DMF to reactants were studied, and a synergistic catalytic mechanism was proposed.