Study Of Electrochemical Method To Synthesis 4, 4'-Dihydroxybiphenyl

4,4'-dihydroxybiphenyl is a fine chemical product with a promising market prospect. The domestic production capacity has maintained very low, lying in a short supply condition. Currently, the research and development of the related synthesis technology must be paid more attention because of the problems as followed:the technique of synthesizing 4,4'-dihydroxybiphenyl is backward and pollution is serious. By the method of indirect electrochemical reaction through organic halides on the cathode to synthesize 4,4'-dihydroxybiphenyl which is a brand-new synthesis method.The electrochemical behaviors and kinetic characteristics of NiCl2(bpy)3 were studied in detail by electrochemical measurements such as cyclic voltammetry, polarization curve and chronocoulometry in DMF medium. The results showed that when the potential range was between 0～-1.70 V(vs SCE), in the condition of low potential scan rate or low concentration, the reduction of NiCl2(bpy)3 underwent two stages.The first, it was reduced by a one-electron process to [Ni(+l)(bpy)3]1+. The second,more negative reaction was assigned to the one-electron reduction of the resultant [Ni(+1)(bpy)3]1+ to Ni(0)(bpy)3.when the scan rate or the concentration of NiCl2(bpy)3 increased to a certain extent, NiCl2(bpy)3 was inclined to produce Ni(0)(bpy)3 directly. In the condition of high potential scan rate and high concentration, the electrochemical reduction of NiCl2(bpy)3 was a quasi-reversible cathodic wave, which was controlled by diffusion and adsorption. The charge transfer coefficient a, diffusion coefficient D and the average rate constant of the electrochemical reaction ks were calculated as 0.27,8.4×10-6 cm2·s-1 and 0.134 s-1 respectively. When the electrode was polarized to -2.10 V, the Ni(0)(bpy)3 could been reduced to [Ni(-1)(bpy)3]-.When the electrode continued being polarized to -2.60 V, the bpy which was dissociated from the complex could been reduced to bpy.The reduction products of NiCl2(bpy)3 could occur chemical reaction in DMF medium,which made the oxidation reaction be a complex process.On the nickel-catalyzed electrochemical coupling reaction, Ni(0)bpy played the catalytic activity. NiCl2bpy was a catalyst precursor. The catalytic reaction had two routes possibly in DMF or ethanol medium, it involved two-step electrochemical reactions and three-stage organic reactions. Ni(0)bpy was a chemical activator through the entire catalytic process in aqueous mediumThe constant current synthetic experiments were tested and the suitable parameters of electrosythesis process in different media were evaluated by self-designed electrobath. According to the current efficiency and yield, the better experimental conditions were obtained by laboratory experiments:In DMF medium, stainless steel as the cathode, magnesium rod as the anode, the current efficiency and yield of synthesizing 4,4'-dihydroxybiphenyl were 25.8% and 63.4% respectively. In ethanol medium, nickel foam as the cathode, iron rod as the anode, the current efficiency and yield of synthesizing 4,4'-dihydroxybiphenyl were 22.8% and 53.7% respectively. In micro emulsion medium, the phenolic hydroxyl group of 4-bromophenol must been protected before the electrolytic, nickel foam as the cathode, nickel rod as the anode, the demethylation was needed after the electrolytic. A 50.2% total yield of 4,4'-dihydroxybiphenyl originated from 4-bromophenol was given by calculating each once through yield.