Facile and Efficient One-Pot Green Synthesis of Benzimidazoles Using Oxalic Acid as an Organocatalyst in Ethanol Solvent

Abstract

An efficient, straightforward, and general synthetic method has been developed for the synthesis of benzimidazoles via the cyclo-condensation of aromatic aldehydes or acids with o-phenylenediamine in ethanol, using oxalic acid as an organocatalyst. This method offers several advantages over existing protocols, including shorter reaction times, improved selectivity, environmentally friendly conditions, simple product isolation, and excellent yields.

Introduction

Organocatalysis is a valuable green chemistry approach that avoids toxic metals and is efficient, selective, and practical. Oxalic acid, a low-cost, stable, and non-toxic organic acid, is explored here as a metal-free organocatalyst for synthesizing benzimidazoles—important compounds with biological and medicinal significance due to their similarity to nucleic acid bases and diverse pharmacological activities. Traditional benzimidazole syntheses often require harsh conditions, toxic reagents, and generate waste, with limited substrate scope.

This study reports the first oxalic acid-catalyzed, one-pot green synthesis of benzimidazoles via cyclocondensation of o-phenylenediamine with aromatic aldehydes or acids in ethanol. The process achieves high yields (85-92%) under mild, solvent-assisted grinding conditions using 10 mol% oxalic acid. Ethanol was found to be the optimal solvent compared to water or ethanol-water mixtures. Various substituted benzaldehydes were successfully converted, demonstrating the method’s efficiency, simplicity, and environmental friendliness. Analytical techniques like IR, NMR, and MS confirmed the product structures.

Overall, this work offers a cost-effective, selective, and sustainable organocatalytic route for benzimidazole synthesis, addressing limitations of earlier methods and aligning with green chemistry principles.

Conclusion

Oxalic acid has been employed as a novel and efficient organocatalyst for the synthesis of benzimidazoles from o-phenylenediamine and a variety of aldehydes or carboxylic acids. The reactions were performed under grinding conditions using a mortar and pestle, with 10 mol% oxalic acid in ethanol as a green solvent, yielding products within 1 to 1.5 hours. This method proceeds under mild conditions, offering short reaction times, high efficiency, and minimal environmental impact. Notably, the catalyst can be recovered and reused for multiple cycles, enhancing the sustainability and practicality of the protocol. Overall, this method offers significant advantages over existing procedures in terms of simplicity, efficiency, and environmental friendliness.

References

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Copyright

Copyright © 2025 Babasaheb V Kendre, Sayas K Lad, Vaishnavi C Giram. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.