Synthesize Of 2,2',5,5'-tetrachlorobenzidine By Pd/C Catalytic-hydrogenation

2,2'5,5'-tetrachlorohydrazobenzene was prepared from 2,5'—dichloronitrobenzene, using 8.0%Pd/C as catalyst in the base media. Some parameters including the hydrogen pressure, the mass fraction and dosage of the sodium hydroxide, the dosage of emulsification and toluene, reaction temperature and co-catalyst was investigated in our experiments. Optimum reaction conditions were determined by experiments as fellows: 20g 2,5 — dichloronitrobenzene was dissolved in 25ml toluene , the pressure of Hb was 1.6MPa, Pd/C 1.0.g, co-catalyst 0.2g, mass fraction of sodium was 15%, the dosage of sodium hydroxide was 18ml, the dosage of emulsification is 1.5g, the reaction time was 55 ℃ 3hours,65℃ 6hours, 80℃ 3hours. The transformation rate of 2,5—dichloronitrobenzene was 100%, the selectivity of TCHB was 84.70%.Some parameters including reaction temperature, mass concentration and dosage of the sulfur acid and reaction time etc, was discussed through different rearranged -methods. Optimum reaction conditions were determined as fellows: the concentration of sulfur acid is70%, the ratio of sulfur acid to raw material TCHB was 10:1,the reaction time was 0℃ 4-6 hours ,and then temperature rise to 40℃, keep this degree 4~6hours, then a little water was used to diluted the sulfur acid, keep this condition 2 hours. For each experiment under optimum reaction conditions, the yields of TCB was 59.76%, the purity of TCB was higher than 94.48%.The reason that the vigor of catalyst was descend was studied, which reveals that the catalyst was not poisoned by Cl~-, 2,5-dichloroaniline. However, vigor of catalyst depended on the size of active carbon. The catalyst can be re-used 3 times.