Synthesis of 3,3’-Dichlorobenzidine by Catalytic Hydrogenation
|School||Qingdao University of Science and Technology|
|Keywords||Nitrochlorobenzene 2,2 ' - Dichlorohydrazobenzene 3,3 ' - dichlorobenzidine Catalytic Hydrogenation Rearrangement|
Nitrochlorobenzene as raw materials in alkaline medium with Pd / C as catalyst, hydrogenation Synthesis of 2,2 'the - Dichlorohydrazobenzene, and 2,2' - Dichlorohydrazobenzene rearrangement in acidic medium to give 3,3 '- dichloro-benzidine. The activated carbon preliminary screening test results show that the more suited to the system with a high specific surface area and a higher content of oxygen-containing groups on the surface of the activated carbon. Titration of surface groups N 2 physisorption and scanning electron microscopy and other methods, as the carrier prepared activated carbon nitrate surface modification on its supported palladium catalyst performance, and the results showed that after different concentrations of HNO 3 after the treatment, the nature of the activated carbon pore structure changed little, but the activated carbon surface concentration of acidic oxygen-containing groups have a greater degree of growth, which provides a large number of adsorption palladium metal particles deposited bit, the degree of dispersion of the palladium metal, to thereby obtain a high activity of Pd / C catalyst, 30% HNO 3 was refluxed in a 60 ° C water bath for 4h processing activated carbon can achieve the best results, the system The activity of the catalyst is obtained without the nitric acid treatment of the activated carbon as the carrier prepared in 2.0 times the activity of the catalyst for nitrochlorobenzene the Catalytic Hydrogenation DHB reaction the DHB yield slightly improved, significantly increased the number of catalyst applied. The experimentally determined by a single factor of catalyst preparation conditions best preparation conditions for the catalyst: dipping solution pH value of 2.5, the concentration of impregnating solution 1.2 g. mL -1 sup>, a dipping temperature 80 ° C, the dipping time 2h, 36% HCHO amount of 4ml 40 ° C to restore 2h and then heated to 80 ° C and continue to restore 1h. The catalyst was prepared under the preferred catalyst preparation conditions for the o-nitrochlorobenzene catalytic hydrogenation reaction, the initial hydrogen absorption rate up to 3370mL. min -1 sup>. g -1 sup> DHB yield of 89.72%. Pd / C catalyst nitrochlorobenzene Hydrogenation of 2,2 '- Dichlorohydrazobenzene experimental results show that the impact on the yield of the main factors is different, including the impact of the mass fraction of sodium hydroxide largest , followed by the amount of catalyst, the third of the amount of cocatalyst, temperature with minimal impact on the yield. By single factor experiment and orthogonal experiment to determine the optimal reaction conditions: 1% Pd / C catalyst amount of 4.5% sodium hydroxide mass fraction of 25%, temperature 65 ℃, 0.267% of the amount of co-catalyst, hydrogen pressure 0.4Mpa, toluene with the o-nitrochlorobenzene quality than 0.87:1. Under optimum conditions, the catalyst activity and stability, the catalyst can be used at least 8 times, DHB used the yield, the reaction time can be controlled between 90% to 93% less than in 330min. By DHB rearrangement Preparation of 3,3 '- dichlorobenzidine hydrochloride experiment compares the different rearrangement method, the effects of temperature, the mass concentration of sulfuric acid, in an amount of sulfuric acid, the reaction time, and many other factors influence stability test, and under optimum conditions of the various factors, 3,3 '- dichloro-benzidine hydrochloride total yield can be as high as 80 ~ 83%, the amino value is higher than 95.0%.