Green Synthesis of Benzimidazole from ο-Nitroaniline and Benzyl Alcohol Catalyzed by Amorphous Iron Oxide

We disclose a sustainable, additive-free strategy for the synthesis of 2-arylbenzimidazoles using a cost-efficient Fe₂O₃-based heterogeneous catalyst. This one-pot cascade reaction, employing benzyl alcohols and o-nitroanilines as substrates, proceeds efficiently under mild conditions. Remarkably, the amorphous Fe₂O₃-200 catalyst delivers dramatically enhanced catalytic performance over its crystalline analogues, affording benzimidazole products in up to 99% yield. Mechanistic investigations attribute this superior activity to the high density of oxygen vacancies and the strong adsorption affinity for benzyl alcohol, which collectively promote the key dehydrogenation step. The catalyst also exhibits outstanding stability, maintaining its high reactivity over five consecutive cycles without a noticeable loss of activity, thereby highlighting its promise for practical and scalable applications.