Development of phosphotungstic acid immobilized amine-grafted graphene oxide as heterogeneous catalyst for synthesis of bis(indolyl) methane derivatives

Phosphotungstic acid was immobilized hydrothermally on the surface of 3-aminopropyltriethoxysilane-grafted graphene oxide (GO-N-PTA) and used as a heterogeneous solid acid catalyst for the synthesis of bis(indolyl) methane derivatives. X-ray diffraction (XRD), fourier transform infrared (FTIR) spectroscopy, BET isotherm, FESEM with EDS and elemental mapping, FETEM, X-Ray photoelectron spectroscopy (XPS), Raman spectroscopy techniques were used to characterize the synthesized catalyst. The catalyst was found to be highly effective for the synthesis of bis(indolyl)methane derivative compounds with yields in the ranges of 94-96.5 % under the optimized reaction conditions. The catalyst was recycled upto 3rd cycle for a specific reaction, that produced 94.5% yield with marginal loss in yield compared to the fresh catalyst (96.5%) depicting the hetreogneiety and sustainability of the present GO-N-PTA catalyst. This study provides the development of sustainable heterogeneous GO-N-PTA catalyst towards the synthesis of highly pharmaceutically important bis(indolyl)methanes derivative compounds.