Graphene oxide: An efficient recyclable solid acid for the synthesis of 2-substituted benzimidazoles from aldehydes and diamines at ambient temperature

Background: Benzimidazole skeletons are found in numerous pharmaceutical agents and in materials applications [1]. The synthesis of benzimidazoles generally requires the heating of o-phenylenediamine and carboxylic acids or their derivatives (nitriles, chlorides, or orthoesters), under strong acidic conditions, sometimes combined with very high temperatures using polyphosphoric acid or by microwave irradiation [2]. Methods: In a one neck flask, aryl aldehydes (1 mmol), diamines (1 mmol) and ethanol (5 ml) were mixed with graphene oxide (GO) at room temperature. After completion of the reaction monitored by TLC, GO was filtrated off and the product was appeared as a solid compound after evaporation of ethanol. The desired product was recrystallized by ethanol and identified by Perkin Elmer FT-IR spectrometer and 1HNMR spectra on Bruker DRX- 300 MHZ NMR instrument. Results: Aromatic aldehydes and diamines were used in the synthesis of 2- substituted benzimidazoles in the presence of GO at room temperature (Scheme 1). High yields, simple and comfortable separate operation provided several special advantages this protocol.Conclusions This method gives remarkable advantages such as simple work-up procedure, using of the green and inexpensive catalyst with excellent yields