The present work deals with synthesis of 2,3-dihydro-1H-1,5-benzodiazepine from o-phenylenediamine and acetophenone at 100 degrees C using a variety of solid acid catalysts, among which 20% w/w Cs2.5H0.5PW12O40 (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.