Graphene oxide-catalyzed C-Sp3-H activation of methylarenes in aqueous medium: A unified metal-free access to amides and benzimidazoles

摘要

Graphene oxide (GO)-catalyzed selective synthesis of amides via C-Sp3-H activation of methylarenes and consequent C-N bond formation with anilines under aqueous medium has been described. Oxygen functionality allied with GO surface played a dual role both as acid catalyst and oxidizing agent to some extent. However, GO has a copious effect on the reaction, shown by a high TOF value with TBHP as co-oxidant. The decisive role of carboxylic acid functional groups on GO nanosheets in this metal-free strategy has been confirmed and was monitored by various analytic techniques viz. Fourier transform-infrared, UV-Vis, Raman and XPS. A plausible mechanism was proposed by control experiments and by the isolation of the intermediate. Over-oxidation of methylarenes was not detected, and high recyclability of the carbocatalyst with its heterogeneous behavior facilitated the isolation and purification of the desired products. We have further explored the utility of this process for the chemoselective synthesis of benzimidazoles.