Microemulsion Preparation Of The Electrochemical Reduction Of Nitrobenzene Aminophenol

P-aminophenol,abbreviated as PAP,is an important organic fine chemical and medicine intermediate,mainly applied to the production of medicines,dyes,developing agents and so on.With the continuous deve lopment of fine chemical industry, the use of aminophenol becomes more and more extensive,and the production market grows very quick-ly.Among different synthses menthods of Aminopheno,electro-reduction of nitrobenzene is the best way to meet with green chemistry, as well as high quality (high purity,low iron content) to meet the need in pharmacy.The cetyltrimethylammonium bromide(CTAB)/n-butanol/nitro ben-zene (NB)/water quasi-ternary phase diagram was drawn by dilution. The structure of microemulsion and the phase transformation was determined by conductivity.The effects of temperature, acidity, zinc sulfate (ZnSO4) concentration on emulsion stability was studied. Results showed that micro-emulsion regions could be formed in larger compo-sition variation of Km=m (C4H9OH)/m (CTAB) value(the mass ratio of co-surface and surface);the liquid phase transition process of microemulsion was continuous;nitrobenzene solubilization capacity increased with the incresing of temperature;water content changed irregularly in the microemulsion with the increasing of system acidity; water content of microemulsion system mainly varied regularly with the increasing of zinc sulfate concentration and the electrical conductivity of system is larger than 2.0 mS.cm-1, which could be reach the requirements of electrosynthesis. The appropriate condition of nitrobenzene electrolysis was determined by experiment:temperature 25℃, the water phase CH+= 5.0mol. L-1, oil content Ro= 30%, zinc sulfate salt concentrations C (ZnSO4)= 0.05mol.L-1,W (NB+EM):W (H2O)=1:1.The electrochemical process of nitrobenzene in microemulsion was studied and discussed by cyclic voltammetry. The study found that, in micro-emulsion, NB on the copper electrode had a good electrochemical activity, NB at the copper electrode in the presence of cyclic voltammetry curves had a hydrogen evolution peak(-0.7v), and the hydrogen evolution potentia more negative than its reduction potential(-0.5v),The reduction of NB on the Cu electrode is an irreversible electrochemical reduction process; The peak potential moved to the negative direction with scan rate of increase, at the same time the peak current value increases; the peak potential with increasing of concentration of dissolved NB shifted to positive, and the peak current increase too; In a certain temperature range, the reaction temperature was favorable for electrochemical reduction of NB. With the increasing of the concentration of sulfuric acid and zinc sulfate, the peak current increased and the peak potential shifted to positive.On the basis above, the constant potential electrolysis was used to study the electrolytic reduction of nitrobenzene in microemulsions,and a series of experimental was carried.The electric potential, the conce-ntration of zinc sulfate, nitrobenzene concentration, pH of system, electric quantity, temperature on the yield of aminophenol were investigated. The best conditions are as follows:Experiments showed that the average yield of p-aminophenol could reach about 67% and 85% electric quantity of theory value when acidity of water phase is CH+=1.2mol.L-1, electrolysis potential was-0.5V, the concentration of ZnSO4 was 0.05mol.L-1, nitro-benzene R0=35% at 70℃.