An Efficient and Eco-Friendly Protocol for Synthesis of 2-Substituted Benzimidazole and Quinoxaline Derivatives by Using Nanostructured Cu2O as Recyclable Catalyst

Abstract

Reconnoitre the use of earth-abundant metals for an essential organic reaction was extremely provocative from an industrial vantage point. In this study, the fundamental and energy-efficient co-precipitation approach was employed to aid the Cu₂O cubed nanostructured catalyst in the generation of benzimidazole and quinoxaline derivatives. The developed Cu₂O cubed nanostructured catalyst was thoroughly evaluated by world-class analytical and spectroscopic techniques. The Cu₂O cube catalyst exhibited exceptional crystallinity, a cubic shape, a large specific surface area and uniformly distributed active sites on its surface. The obtained astounding structural and physico-chemical characteristics successfully enabled the catalytic activity for the synthesis of benzimidazole and quinoxaline. The recognised vital structural and physical attributes substantially improved the catalytic activity for the production of benzimidazole and quinoxaline derivatives over mild reaction conditions. Employing a cubic Cu₂O catalyst, diverse reaction parameters have been examined, encompassing the effects of catalyst dosage, temperature, time, solvent, yield and substrate scope. As a result, the designed catalyst was used to synthesise heterocyclic 2-substituted benzimidazole and quinoxaline derivatives via the condensation of o-phenylenediamine, aldehydes and 1,2-diketone. The reported results showed 100% conversion in both aimed products, with 90% selectivity for 2-substituted benzimidazole and 95% selectivity for quinoxaline derivatives, respectively. The obtained yield for 2-substituted benzimidazole and quinoxaline derivatives was 85 and 98 at 60°C for 3 and 4 h, individually. The catalytic activity was fully based on the inherent properties of cubic Cu₂O. On top of that, all synthesised compounds were structurally validated by ¹H NMR, ¹³C NMR and mass spectrum data. Remarkably, the efficient cubic Cu₂O catalyst demonstrated impressive recyclability for up to six consecutive cycles with minimal loss of its initial catalytic activity. The spent cubic Cu₂O catalyst's characteristic results revealed evidence for its stable structural and physico-chemical features. In addition, we endeavoured to propose and describe a plausible reaction mechanism utilizing the developed nanostructured Cu₂O cubes for the synthesis of benzimidazole and quinoxaline derivatives.