Synthesis Of 5-Aminobenzimidazolone And Benzimidazole Derivatives

5-Aminobenzimidazolone is the main intermediate of the pigments of benzimidazolone structure.With the development of the plastics,ink and paint industry,a sharp increased 5-aminobenzimidazolone demand appears.Traditional synthetic method has some serious disadvantages such as poor product quality,a large number of waste water and waste residue produced in the production process.Synthesis of 5-aminobenzimidazolone from 2,4-dinitrochlorobenzene is studied.And reaction conditions of this synthetic route through 4-nitro-1,2-phenylenediamine is researched. The optimal condition of ammonia reaction is 1 equv.2,4-dinitrochlorobenzene,3 equv. ammonia,chlorobenzene as solvent,145-150℃,1 h.The best selective reduction of 2,4-nitroaniline is performed in the excess 30%of sodium disulfide aqueous solution at 65-70℃for 1 h.The proper condition of cyclization is that the mole ratio of 4-nitro-1,2-phenyl-enediamine to urea is 1:2.2 and temperature is kept at 165-170℃for 1 h and then to 200℃for 2 h.The proper condition of reduction of 5-nitrobenzimidazolone is 8%wet Raney Ni, methanol as solvent,at 145-150℃,under 1.0-1.5 MPa for 5 h.The total yield over four steps is 71.4%.The advantages of this synthetic route are low cost of raw material,high purity of product,easy operation and little environmental pollution.So it is suitable for large-scale industrialization.A one-pot synthetic of benzimidazole directly from o-nitroaniline is studied in this paper. The optimum condition has resulted from experiments.Benzimidazoles are prepared by o-nitroanilines in the presence of selenium(or selenium dioxide),potassium carbonate, ammonium acetate,water and DMF.This is a new synthetic method of benzimidazoles.And the proposal mechanism catalyzed by selenium and selenium dioxide is put forward.