Role of graphene oxide as a heterogeneous acid catalyst and benign oxidant for synthesis of benzimidazoles and benzothiazoles

We report the synthesis of benzothiazoles and benzimidazoles using graphene oxide as an effective catalyst with good yields and easy recyclability. Graphene oxide plays the dual role of a metal-free acid catalyst and an oxidizing agent. The mechanism of action of graphene oxide as a catalyst was confirmed using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopy. Good yields were obtained at 60 °C as well as under ultrasonic irradiation at 35 °C with methanol as the solvent. Additionally, this is also the first report in which the regeneration of partially-reduced spent graphene oxide has been carried out to restore the oxygen containing functional groups and provide a path for the reuse of graphene oxide as the catalyst and oxidizing agent. Graphene oxide plays a dual role as active metal-free acid catalyst and as non-toxic oxidant for benzothiazole and benzimidazole synthesis. Isolated partially reduced graphene oxide was re-oxidized to regenerate the catalyst and restore its activity.