Synthesis of 2-Substituted Benzimidazoles and 1,5-Disubstituted Benzodiazepines on Alumina and Zirconia Catalysts

Abstract

In this study, alumina, zirconia, manganese oxide/alumina, and manganese oxide/zirconia have been investigated for their catalytic activity in the condensation reaction between o -phenylenediamine and an aldehyde or a ketone to synthesise 2-substituted benzimidazoles and 1,5-disubstituted benzodiazepines respectively. Surface area, surface acidity, and morphology of the catalysts have been analysed and correlated with their catalytic activity. The isolated yields of 2-substituted benzimidazoles and 1,5-disubstituted benzodiazepines are in the range of 30% to 95%. A good correlation between the amount of surface acid sites as well as the surface morphology of the catalysts and the catalytic activity has been observed. This method has been found to be simple and economical. The solid supports could be regenerated and reused without much loss in their activity. Further, the solid supports have been also found to be effective as general catalysts in the condensation of o -phenylenediamine with other substituted aldehydes and ketones. The presence of amount of surface acid sites, morphology of the catalyst, and presence of manganese oxide on the surface of the catalyst plays a synergistic role in the synthesis of benzimidazoles and benzodiazepines.