Benzimidazoles and their derivatives are the important intermediates for pharmaceutical and biological fields. They have been used as antiulcerative, antihypertensives, antivirals, antifungals, anticancers, antitumor, antihistamines and antihelminithic agents [1]. The most popular method for synthesis of benzimidazoles is the coupling of phenylendiamines derivatives with carbonyl compounds like carboxylic acid, nitriles, imidates, orthoesters and aldehydes which often requires strong acidic conditions and sometimes very high temperatures [2]. Various catalysts which also act as oxidative reagent have been used for this purpose like sulfamic acid, DDQ, Oxone, FeCl3.6H2O, In(OTf)3, Yb(OTf), Sc(OTf)3 and KHSO4 [3]. In this work we used a versatile method for the synthesis of benzimidazoles from the reaction of ortho-phenylendiamin with different aldehydes in presence of Fe(HSO4)3 as an oxidative catalyst. All the reactions were preceded in water as an environmentally benign solvent with high yields and easy isolation of products at room temperature.

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