Rapid and Cheap Synthesis of Benzimidazoles via Intermittent Microwave Promotion: A Simple and Potential Industrial Application of Air as Oxidant

Abstract

Using inexpensive KI as the catalyst in the presence of ambient air, benzimidazoles were synthesized from aromatic aldehydes and o-phenylenediamine with excellent yields via intermittent microwave irradiation without reflux equipment. The synthesis process was mild and only needed only a short reaction time (7–10 min). As a simple example of the utilization of molecular oxygen under mild conditions, this method provides a novel way to synthesize benzimidazoles. The industrial synthesis of benzimidazoles may be realized by a cycle of microwave irradiation.

Keywords:

• Ambient air
• benzimidazole
• intermittent
• microwave promotion
• molecular oxygen

ACKNOWLEDGMENTS

The authors are grateful to the National Natural Science Foundation of China (No. 20772035) and the Natural Science Foundation of Guangdong Province (No. 5300082) for the financial support of this work and to Dr. David E. Finlow (Shawnee State University) for helpful language correction.

Notes

^a All reactions catalyzed by SnCl₂.

^b Isolated yield via recrystallization or column chromatography.

^c Grinding synthesis.

^a All reactions intermittently promoted by a 320-W domestic microwave oven using DMF as the energy transfer medium, and the reaction time was 40 s × 10.

^b Isolated yield via recrystallization or column chromatography.

^a All reactions carried out in the presence of DMF as energy transfer medium and catalyzed by KI (15 mol%). All products were isolated via recrystallization or column chromatography and confirmed by spectral data (IR, ¹H NMR, and ¹³C NMR).