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Multifunctional succinimide-based ionic liquids (SIILs) were well-designed and synthesized, and they were used as a dual solvent–catalyst for efficient transformation of CO2 and 2-aminobenzonitriles into quinazoline-2,4­(1H,3H)-diones under mild conditions. The catalytic behaviors, including the effects of anion–cation structures and reaction parameters, catalyst recyclability, and versatility were thoroughly studied. The optimum [HTMG]­[Suc] comprising a tetramethylguanidine cation and a succinimide anion showed excellent activity toward various substituted 2-aminobenzonitrile substrates. [HTMG]­[Suc] was easily recyclable with superior structural integrity. The possible pathways of CO2 and 2-aminobenzonitrile activated by [HTMG]­[Suc] were investigated in depth, which supported the reaction mechanism well. In comparison with reported catalysts, the protocol herein exhibited comparable catalytic performance under milder and greener conditions without any additional organic solvents.

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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.