Study Of Electrochemical Synthesis Technology Of 2,2'-Dichlorohydrazobenzene

Through translocation rearrangement reaction in acidic medium,2,2'-Dichlorohydrazobenzene(DHB) could transform to 3,3'-dichlorobenzidine (DCB) which is an important intermediate in synthesis of yellow dye. This series of dyes account for about a quarter in organic dyes. DHB was mainly prepared by using zinc powder, aluminum powder, hydrazine hydrate, and catalytic hydrogenation method, etc. With the increasingly serious environmental problems and rising costs of labor and raw material, the tranditional methods had disadvantages in many aspects, such as serious pollution, complex operation, security risks and more usage of precious catalysts. There are more and more limitation on its application and development. The electrochemical reduction method using ion-exchange membrane has got more attention from researchers because of the advantages, such as cleaning, environmentally friendly, producing less waste, simple, low temperature and pressure.In this paper, porous stainless steel was used as anode, and composite electrode made by nickel foam and steel mesh was used as cathode in this self-made cell. Nafion membrane was used as a diaphragm between the anode and cathode. Focusing on the effect of catalyst on the reaction, we compared the catalytic abilities of three different catalysts, i.e. litharge, lead tetroxide, lead nitrate, and discussed the effect of the mode of loading, activation and dosage of the catalyst on reactions. The possible catalytic mechanism was also deduced. The effects of different initial current and temperature, different concentration of anolyte, different electrode materials and membrane on the reaction were investigated.The three catalysts were characterized by XRD after activation, and the result showed that litharge was a key role. The cathode plates were characterized by cyclic voltammetry, and it was found that the activated electrodes were more active than before. The electrode potential was tested by dynamic scanning potential, and the result showed that the electrode potential was lower after activated by litharge. The dispersion of the catalyst coating in the electrodes was characterized by SEM, which showed that the activated catalyst was dispersed on the surface of the electrode uniformly and that provided a good place for the absorption of raw materials. Finally, the possible reaction mechanism was deduced, finding that the catalyst worked in the raw materials transforming to intermediate, but the catalyst is not a key role when the intermediate product transformed to the desired product. It was found that the initial current density of this experiment should be chosen in the 1.1 A/dm2, the choice of initial temperature chosen at 65℃, and the 25%(mass fraction) sodium hydroxide solution is proper for anolyte. The synthesis yield of DHB was up to 96%.At last, the electrochemical after-treatment process was studied. It was found that the yield of product is ideal with the anolyte and catholyte recycled after the reaction. This indicated that the recycled process was a green synthetic process. After studies on the catalyst cycle utilization in the reaction, it was found that the catalyst on the electrode can still recycle, but the reaction time increased half-hour.