Synthesis And Improvement On Process Of 5-Aminobenzimidazolone-2

5-Aminobenzimidazolone-2 is an important pigment intermediate, which is mainly used in synthesizing benzimidazolone pigments.In the paper, benzimidazolone-2 was obtained by reacting o-diaminobenzene with urea in the presence of water with the yield of 91%. And then 5-nitrobenzi- midazolone-2 was prepared by nitration of benzimidazolone-2 with condensed nitric acid in the presence of chlorobenzene as solvent. Finally, 5-aminobenzimidazolone-2 was obtained by using three reduction methods. The yield was 77% with the iron methods. The yield was 91% with liquid-phase hydrogenation by using Raney Ni catalyst. The yield was 95% with liquid-phase hydrogenation by using Pd/C catalyst.The method of Liquid-phase hydrogenation by using Raney Ni catalyst was studied with emphasis in the paper. Six different types of Raney Ni were obtained by reacting Al-Ni alloy with sodium hydroxide solution to solve the Al in the alloy. The high pressure reactor was used as the main reaction apparatus. The appropriate reaction condition was obtained. The amount of the catalyst was 4%~5% (weight percent in nitro compound). The Raney Ni was recycled for four times. And 1% new catalyst was added in the fifth recycled process. The solvent was ethanol and the amount was 120mL per mol nitro compound, which could be recycled above 80%. The reaction temperature ranged from 90℃to 95℃. The pressure was about 2 MPa. The product was purified by recrystallization in which the mother liquid was recycled for 20 times. The yield of 5-aminobenzimidazolone-2 was about 91% with the purity of 99.0%. The melting point was 251~253℃.In the three reduction methods, the cost, the process and the influence on the environment were compared. The optimal reduction was the liquid-phase hydrogenation method by using Raney Ni catalyst, with the advantage of high yield, high quality, little pollution, simple process and low cost.Starting from the o-diaminobenzene, 5-aminobenzimidazolone-2 was obtained with the method liquid-phase hydrogenation method by using Raney Ni catalyst. The overall yield was 79.5% with the purity of 99.0%. As the small-scale reaction succeeds, the technology will be put into production in Shandong Province.