La–Mg mixed oxide as a highly basic water resistant catalyst for utilization of CO₂ in the synthesis of quinazoline-2,4(1H,3H)-dione

Abstract

The synthesis of quinazoline-2,4(1H,3H)-dione was done by direct utilization of CO₂ in the cyclization of 2-aminobenzonitrile (2-ABN) using lanthanum magnesia mixed oxide (La–Mg MO) as a strong basic catalyst under mild reaction conditions in water. It gave a conversion of ∼92% with 100% selectivity at 140 °C in 14 h. La–Mg MO was prepared by hydrothermal method using urea as homogeneous precipitating agent. The catalyst was characterized by different analytical techniques like BET, XRD, FT-IR, SEM, and TGA, and the basicity by CO₂-TPD and acidity by NH₃ TPD. Various reaction parameters were studied to predict the reaction mechanism and kinetics. The reaction follows the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type kinetics model with an apparent activation energy of 23.3 kcal mol⁻¹. The catalyst was recycled three times with an insignificant change in activity. The overall process is clean and green.