Study On Catalytic Transfer Hydrogenation For Synthesis Of 3,5-Dihydroxybenzoic Acid

Catalytic transfer hydrogenation in presence of catalyst and hydrogen donor as hydrogen source is an effective method for organic synthesis. This method is of several advantages: mild reaction conditions, simple equipments and safety for carrying out. In this thesis, the proper catalysts and related reaction conditions for the synthesis of 3,5-dioxocyclohexane carboxylic acid, a important pesticide intermediate prepared from 3,5-dihydroxybenzoic acids via catalytic transfer hydrogenation on the supported Pd catalyst, has been investigated.Firstly, resorcinol was used as a model compound to prove the feasibility of supported Pd catalyst system for catalytic transfer hydrogenation. The catalysts were prepared by impregnation and precipitation method, and the active carbon, γ-Al2O3, silica and kieselguhr were selected as the carriers of catalyst. the effects of reaction conditions, such as reaction temperature, types of solvents, and types of hydrogen donors were investigated, It was found that the Pd/C catalyst was the best one, and its proper reaction conditions were also obtained as follow: sodium formate as hydrogen donor, water as solvent, reaction temperature of 70℃ and reaction time of 2.5h. Enhancing the temperature from 70℃ to 90℃, the catalyst could show excellent catalytic properties for the hydrogen transfer hydrogenation of 3,5-dihydroxybenzoic acid, whose conversion could reach to >92%, and the selectivity of product >97%. Using the methods of UV, TLC, HPLC, IR, 1H NMR and elementary analysis, the object product was identified, and the exact quantitative analysis method of HPLC for raw materials and main products was determined.In order to improve the catalytic performance of Pd catalyst system, the supported bimetal catalysts of Pd-Me/carrier (Me= Ba, Bi, Co, La, Ce, Cu), were designed and prepared. Using the techniques of BET, XRD, TPR, TPD, TG-DTA, XPS, SEM and TEM, the catalysts were characterized systematically. It was found that Pd-Co/active carbon catalyst was the optimal catalyst, and Pd-Co/γ-Al2O3 was also good, but silica and kieselguhr were not proper carriers for the object reaction, because of their stronger surface acidity, which could result in the formation of polymer, jammed the micro pores of catalyst, and then resulted in its deactivation. Addition of Bi, Ce and Cu promoters could not improve the activity of catalyst, but La and Ba promoter could enhance the activity of catalyst apparently, and the Co was the best promoter, especially Co was impregnate in advance. It was attributed to that the pre-impregnated Co may occupy the micro pores of active carbon, and cover some bad functional groups on the surface of catalyst, so that the active and selectivity of catalyst could be enhanced obviously.With the optimized catalyst of Pd-Co/C, the kinetic experiments were carried out, and the macroscopic kinetics equation was obtained as follow:It was found that object reaction is 0 order reaction as for the concentration of 3,5-dihydroxybenzoic acid, and 1 order for that of hydrogen donor of sodium format and that of the related catalyst. The adsorption process of sodium format was the rate determine step, when its concentration is much greater than that of reactant 3,5-dihydroxybenzoic acids.