The Technical Study On Electrochemical Synthesis Of Hydrazobenzene

Benzidine compound which is synthesized by the intramolecular rearrangement of hydrazobenzene under acidic conditions is an important organic azo dye intermediate. The industrial technology of synthesis of benzidine from hydrazobenzene is very successful, for example, zinc powder reduction, iron powder reduction, formaldehyde reduction, hydration-hydrazine reduction, catalytic hydrogenation reduction and so on. However, there are still many defects in the synthesis methods of DHB such as high cost, serious environment pollution, and low yield. In this experiment, we synthesize DHB by electrochemical method because of its advantages, such as environment-friendly, high yield, low cost, short process flow and so on.In this paper, the optimal reaction conditions of electrochemical synthesis of 2,2’-dichlorohydrazobenzene from o-chloronitrobenzene and 2,2’-dimethoxyhydrazobenzene from o-nitroanisole were studied. In the experiment of synthesis DHB, we controlled stainless steel plates as anode plates, foam nickel plates as the cathode plates, the temperature in the anode compartment at 80℃, electrode spacing of 2 mm, the current intensity of 2.86 A/dm2 (the electrolysis mode of parallel circuit), and the stirring speed of 750 r/min. The effects of different numbers, different types, and different amounts of catalyst on the synthesis experiment were studied. The results indicated that the reaction time was 6 h, and the yield of DHB was as high as 93% when the catalyst was PbO. For the industrial production of DHB, we experimented with the stainless steel plate and the stainless steel-Ni plate that a layer of foam nickel was coated on the surface of stainless steel plate as the cathode plates. The results showed that the reaction time was 6 h and the yield was 95% when the stainless steel-Ni plate as the cathode plate. In the reduction of o-nitroanisole, the effects of current density, mass concentration of raw material, the amount of catalyst and the different cation-exchange membrane on the reduction reaction were studied. Finally, the reaction time was 7 h, and the yield of DHB was as high as 92.19%, when the current density was set as 2.86 A/dm2, the mass fraction of raw material was 5%, the mass fraction of the NaOH solution respectively were 25% and 5% in the anode and cathode cells, the electrolysis temperature set at 85℃ and the agitation rate was 750 r/min.Through year’s efforts in the lab, the technology on electrochemical synthesis of 2,2-dichlorohydrazobenzene was very successful, so we expanded the device to the pilot experiment. In the pilot experiment, the electrolytic cell was welded by steel plate (the thickness of 1 cm), and the catholyte was stirred by the circulating pump. Finally, we compared the yield of DHB under the different mass fraction of raw material, and the results showed that the content of o-CA was 5%, DHB was 93% and DOB was 2%, when the electrolysis temperature set at 80℃,...