Green Synthesis Of2-Benzimidazoles

Benzimidazoles are important drug intermediates with biological activity, and they havefound wide applications in many areas. Synthesis of benzimidazoles has attracted muchattention in recent years, but most of the traditional methods suffer from some seriousproblems. Thus, developing efficient and environmental friendly synthetic methods hasimportant theoretical and practical values. Thus, synthesis of2-benzimidazoles fromaldehydes and o-phenylenediamines using hydrogen peroxide as oxidant has been studiedfrom three different catalytic oxidation system in this paper.Firstly, a novel sodium iodide and ammonium molybdate co-catalytic system wasdeveloped for the synthesis of2-benzimidazoles using hydrogen peroxide under ultrasoundirradiation. Comparing with general methods, the remarkable advantages of this method areits high efficiency, mild reaction conditions, and small amounts of green reagents, which is inline with the concept of green chemistry.Considering the prominent advantages of supported catalysts, special attention has beenconcentrated on the effect of the supports in attempt to establish an efficient and convenientsynthetic method for2-benzimidazoles. The research results showed that SiO2supportedammonium molybdate exhibited high activity but poor stability due to its planar structure. Incontrast, TiO2and γ-Al2O3supported ammonium molybdate were found to have good activityand stability, ascribed to the highly dispersed active species and porous structure of supports.Finally, a novel magnetic core-shell Fe3O4@SiO2@(NH4)6Mo7O24catalyst was preparedand demonstrated to be an efficient catalyst for the synthesis of2-benzimidazoles. It can beseparated from the reaction mixture by an external magnetic field, and recycled and reusedwithout any appreciable loss of catalytic activity. Meanwhile, adequate characterizations wereemployed to clarify the relationship between the special structure and high catalyticperformance of this novel catalyst.