The room-temperature, ambient-pressure conversion of CO2 into value-added pharmaceutical products quinazoline-2,4(1H,3H)-diones

Abstract

As global warming due to CO₂ emissions has become a widely recognized concern, CO₂ capture, sequestration, neutralization, and conversion have become possible solutions to address this concern. Among these approaches, the conversion of CO₂ into fuels or value-added products has attracted considerable attention. In this work, we report the high-efficiency conversion of CO₂ to important industrial raw materials for pharmaceutical compounds, quinazoline-2,4(1H,3H)-diones, via reactions with 2-aminobenzonitriles at room temperature and under ambient pressure, with high conversion yields (91.5–99.3%). 1,8-Diazabicyclo-[5.4.0]-undec-7-ene (DBU), 1,1,3,3-tetramethylguanidine (TMG), and cholinium (Ch) ammonium-based ionic liquids (ILs) are employed as catalysts during the process. Cations with a pK_a value near 11.9 and anions with a pK_a value range of 10 to 15 are necessary for the reaction. The experimental results indicate that the ionic liquid pair [HDBU⁺][3-Cl-PhO⁻] has high efficiency under very mild conditions, obtaining high product yields of 91.5% at 25 °C and 1 atm and 99.3% at 30 °C and 1 atm. More importantly, the catalysts retain high efficiency and activity after 5 consecutive cycles. To gain insightful understanding of the reaction, density functional theory (DFT) calculations were conducted to study the reaction mechanism. The computational results indicate that the catalytic process contains three stages: cyano activation, intramolecular rearrangement, and intramolecular cyclization. Of these, the rate-determining step is cyano activation, which shows an energy barrier of 24.5 kcal mol⁻¹. Tuning the types of ions in ILs can effectively reduce this energy barrier and allow high efficiencies.