Selective Green Synthesis of 1,5-Benzodiazepine over Modified Heteropolyacid as Nanocatalyst: Kinetics and Mechanism

The present work deals with synthesis of 2,3-dihydro-1H-1,5-benzodiazepine from o-phenylenediamine and acetophenone at 100 °C using a variety of solid acid catalysts, among which 20% w/w Cs_2.5H_0.5PW₁₂O₄₀ (Cs-DTP)/K-10 clay was the best. The effects of various parameters such as speed of agitation, catalyst loading, mole ratio of 1,2-diamine to acetophenone, and temperature were studied with 20%w/w Cs-DTP/K-10 to establish kinetics of the reaction. The catalyst was found highly active, robust and reusable. The reaction follows Langmuir–Hinshelwood–Hougen–Watson type of mechanism with weak adsorption of all species. The apparent energy of activation is 9.39 kcal/mol. The studies were extended to synthesis of various derivatives of benzodiazepines, which are biologically active.