Exploration of catalytic species for highly efficient preparation of quinazoline-2,4(1H,3H)-diones by succinimide-based ionic liquids under atmospheric pressure: Combination of experimental and theoretical study

Abstract

Cyclization reaction of carbon dioxide (CO2) and 2-aminobenzonitriles is of significance for the sustainable development, however, the harsh reaction condition especially for the high CO2 pressure is still an obstacle. Herein, a novel ionic liquid benzyltrimethylammonium succinimide ([BzTMA+][Suc−]) is designed and synthesized, in which no active hydrogen atom is included in cation. It displays the excellent catalytic activity achieving the 98.8% yield for quinazoline-2,4(1H,3H)-diones even under the atmospheric pressure. By combination of nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR), CO2 absorption measurements, densityfunctionaltheory (DFT) calculations, and the frontier molecular orbital analysis, the real catalytic species and synergistic effect of cation and anion on the catalytic performance are elucidated. The [Suc−] anion affords to introduce the CO2 into the organic phase even under the atmospheric pressure by formation of [Suc-CO2−]. However, the real catalytic species is [BzTMA+] cation and [Suc−] anion rather than [BzTMA+] and [Suc-CO2−]. If the active hydrogen atom is included in the cation, the CO2 absorption capacity of [Suc−] anion would be weakened by the strong interaction between active hydrogen atom in cation and [Suc−] anion resulting in the inferior catalytic behavior. The cooperation of [BzTMA+] and [Suc−] finally results in the high catalytic activity under the atmospheric pressure. Involvement of active hydrogen atom in cation is not an insurance to prepare the robust catalyst.