CO2 involved synthesis of quinazoline-2,4(1H,3H)-diones in water using melamine as a thermoregulated catalyst

In this study, pharmaceutically relevant quinazoline-2,4(1H,3H)-diones were synthesized eco-efficiently by cycloaddition of CO2 and 2-aminobenzonitrile in water, catalyzed by melamine as a thermoregulated catalyst. Quinazoline-2,4(1H,3H)-dione was produced selectively with 92% yield at 120 °C, 4.2 MPa, and automatically separated from the hot catalytic aqueous solution, which was reused directly for several runs until its activity decreased in an obvious manner. Then, the catalyst melamine was recrystallized from the spent aqueous solution via simple cooling and reused for another several catalytic runs. The efficient valorization of CO2 and the straightforward stepwise recovery of the products and catalyst were important to save energy and minimize process waste for the practical industrial production.