Synthesis Of 5,6-diaminobenzimidazolone

Benzimidazolone derivatives pigments are widely used and 5,6-diaminobenzimidazolone are of critical importance in pigments synthesis. A rational route for 5,6-diaminobenzimidazolone is designed. DSC,TCL,MS,HPLC,IR,1H NMR,13C NMR and elemental analyses are properly used for the characterization of the intermediates and the target product.o-Phenylenediamine condensed with urea to give benzimidazolone which underwent nitration with concentrated nitric acid and sulfuric acid.5,6-Dinitro benzimidazolone was obtained from the nitration mixture by recrystallization. Catalytic hydrogenation was conducted on 5,6-dinitrobenzimidazolone to get 5,6-diamino benzimidazolone. Optimized process conditions were investigated as follows. In nitrogen atmosphere, the condensation was conducted during 8h with the mole ratio of urea to o-phenylenediamine 1.3 at 160℃. Benzimidazolone was recrystallized from ethanol solution of high purity in 87% yield. Nitration of benzimidazolone gave 5,6-dinitrobenzimidazolone in 69% yield. Therefore, benzimidazolone was introduced into sulfuric acid while stirring at 0℃followed by dropwise addition of concentrated nitric acid and sulfuric acid mixture(n(nitric acid):n(benzimidazolone)=2.2). The mixture was stirred for further 6h under 0℃. Pure 5,6-dinitrobenzimidazolone was separated from acetone solution. Iron reduction was conducted under inert gas atmosphere to get the pure sample of 5,6-diaminobenzimidazolone. Then, the catalytic hydrogenation of 5,6-dinitrobenzimidazolone was studied using Raney-Ni to get 5,6-diaminobenzimidazolone. Single-factor experiment was investigated to obtain the optimal conditions of catalytic hydrogenation. And 5,6-diaminobenzimidazolone of 99.6% purity was got in absolute alcohol in 90% yield by Raney-Ni catalytic hydrogenation of 5,6-diaminobenzimidazolone with hydrogen under the condition of 100℃,2.5MPa, Raney-Ni/5,6-diaminobenzimidazolone=9% (mass fraction). Therefore, the total yield of the three-step reaction is 54% which is nearly 46% higher than that of the five-step route from 1,3-dichlorobenzene. Research on Raney-Ni catalyst synthesis and recycling were also investigated and the results demonstrated that the Raney-Ni maintained high activity and selectivity after recycling three times.5,6-Diaminobenzimidazolone was successfully synthesized using starting material of o-phenylene diamine by three-step process. Single-factor experiment was conducted to optimize the reaction conditions.5,6-Diaminobenzimidazolone was prepared in an overall yield of 54% which is suitable forindustry production.