Electrochemical Reduction Of Nitrobenzene In Sulfuric Acid Solution And Microemulsion Preparation 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. There are four kinds of methods to synthesize PAP now: (1) Reduction of p-nitrophenol by pulverized iron, (2) Catalytic hydrogenation of p-nitrophenol, (3) Catalytic hydrogenation of nitrobenzene, (4) Direct electro-reduction of nitrobenzene(NB). Among these methods, the electro-reduction of nitrobenzene method is the best way that agrees with the development of green chemistry. At the same time it can yield high quality product (high purity, low iron content), to meet with the need in drugs. Direct electro-reduction nitrobenzene to p-aminophenol on copper electrodes in sulfuric acid systems and micro-emulsion systems is studied in this dissertation. The synthetic technology has also been discussed.The cathodic reduction behaviors and kinetic characteristics of NB in sulfuric acid was studied by cyclic voltammetry, results showed that a hydrogen evolution peak existed and the value was more negative than that of nitrobenzene, it was also found that reduction process is irreversible, the peak current of reduction of NB in Sulfuric acid increased with the increase of scanning rate , temperature and Concentration of NB. The electrode process was controlled by diffusion, and only the dissolved nitrobenzene can be reduction on the copper electrode.The experimental condition, such as temperature, concentration of NB,concentration of H₂SO₄ and electric quantity of NB to PAP on Cu, has been optimized by constant potential electro-synthesis. Results showed that the average yield of p-aminophenol could reach 94% and electric quantity could reach 85% of theory value, when the process takes place in 2.0 mol·L^-1 nitrobenzene solution with 20% sulfuric acid and 0.1 mol·L^-1 medium concentration at 65℃.Phase diagrams of the pseudo-ternary -component of CTAB/C₄H₉/ n-C₇H₁₆/H₂O system were plotted by dilution method. The structure of micro-emulsion in the system of CTAB/C₄H₉OH/n-C₇H₁₆/H₂O was determined by conductance measurement. The concentration of NB in micro-emulsion was researched under different temperature and acidity on micro-emulsion, result indicated that micro-emulsion regions can be formed in larger composition variation of W_Emulsifier=W_C4H9OH/W_CTAB value(the mass ratio of co-surface and surface ). In addition, the micro-emulsion regions are insensitive to temperature. With the increase of aqueous acidity, the water content of the micro-emulsion system shows irregular changes. The concentration of NB in microemulsions increased with the increase of oil, but decreased with f acidity and water content in microemulsions.The cathodic reduction behaviors and kinetic characteristics of NB studied in micro-emulsion system acid by cyclic voltammetry showed that the NB could be easier reduction on copper and was also an irreversible process. the peak current increased with content of NB. the cathodic reduction could be easily take place with higher temperature. Experiments showed that the average yield of p-aminophenol could reach about 68% and 100% electric quantity of theory value when acidity of water phase is 5.0 mol·L^-1. reaction, nitrobenzene concentration is...