Abstract Efficient hydrogenation of o-aminonitrobenzenes on palladium-containing granulated carbon catalysts in carboxylic acid solutions was accompanied by cyclization into aminobenzimidazoles. A simple hydrogenation reactor with a fixed gauze holding a reusable granulated catalyst was designed. Acylated and sulfonylated 4 (7)- aminobenzimidazoles were obtained. In terms of electronic and geometrical parameters, ...