Synthesis Of Diphenyl Carbonate By Oxidative Carbonylation With Heterogeneous Palladium Complex Catalysts

Diphenyl Carbonate (Diphenyl Carbonate, DPC) is the main intermediate for synthesizing the general engineering material-PolyCarbonate (PolyCarbonate, PC). At present, the main synthetic methods of DPC contain phosgene method, transesterification method and phenol oxidative carbonylation method. Oxidative carbonylation can effectively avoid the shortages associated with another two methods, including the use of toxic phosgene raw materials, the complex reaction process, and the more by-products and so on. As compared with the former two methods, oxidation carbonylation method has a lot of advantages such as high atom utilization rate, non-toxic reaction, fewer by-products, which accords with the requirements of green chemistry and low-carbon economic development model, and it has already become the major developing direction of DPC synthesis all over the world.Oxidation carbonylation method mainly focused on the selection of catalytic system, including the selections of main catalyst and catalyst promoter. The entire catalytic reaction is achieved in the fixed bed, fluidized bed and high pressure reactor, and many problems, such as the difference of mass and heat transfer as well as large pressure drop would existed in the reaction process. Thus the catalytic system needs to be designed according to the complexity of reaction process. The catalytic system can be divided into heterogeneous load and homogeneous complexes. Heterogeneous load mainly loads active component on the carriers (perovskite, molecular sieve etc). This method facilitates the separation between the catalyst and reactants after the reaction, but the catalyst activity is usually not very high. On the other hand, the homogeneous complexes can significantly increase the yield of products. The ligand containing P, N, P-P, N-N and other heterocyclic ligands are commonly used in homogeneous complexes catalyst. This method can also solve the problem of falling off of active components by designing different ligands, thereby improve the catalyst life.In this work, four types of catalysts [1,1’-Bis(diphenylphosphino) ferrocene] dichloropalladium (DPPF),[1,2-Bis(diphenylphosphino) ethane] dichloropalladium (DPPE),(1,3-Bis(diphenylphosphino)propane) palladium(II) chloride(DPPPr),1,4-Bis(diphenylphosphino)butane-palladium(II) chloride (DPPB) were synthesized by using diphenylphosphino as ligand and PdCl2as active component. The structure and propertie of different catalysts were characterized by IR,1HNMR, EA, and TG methods. Meanwhile, the synthesis of diphenyl carbonate catalysts by catalytic oxidation of phenol carbonyl were investigated, and the conclusions were obtained as follow:(1) Four types of catalysts,[1,1’-Bis(diphenylphosphino)ferrocene] dichloropalladium (DPPF)%[1,2-Bis(diphenylphosphino) ethane] dichloropalladium (DPPE)、(1,3-Bis(diphenylphosphino)propane) palladium(II) chloride (DPPPr)、1,4-Bis(diphenylphosphino) butane-palladium (II)chloride(DPPB), were synthesized in this work by using diphenylphosphino as the raw material. The demand in reaction temperature increased with the increasing of the distance between two P atoms during the process of preparing complexes.(2) The catalytic activity order of the four kinds of catalyst is DPPF-PdCl2>DPPE-PdCl2>DPPPr-PdCl2>DPPB-PdCl2. This results obtained by the introduce of ferrocene in the complexe, which is an electron-rich group and can effectively give electronic back to palladium after cooperating, causing an increase in the electron cloud density of palladium to make the coordination bond more stable, and then the catalytic activity was improved.(3) In choosing catalyst promoter (mainly inorganic promoter), we found that the activities of CuCl2、CuCl、Ce(NO3)3are stronger than Mn(NO3)2and Co(NO3)2. With the further study, we found that the redox potential of CuCl2, CuCl, Mn (NO3)2is higher than that of Pd2+/Pd0(0.99V) and [PdBr4]2-/Pd0(0.64V), but lower than that of O2/H2O (1.23V). Pd0to Pd2+can be effectively oxidized and the oxidation reduction cycle of the catalytic system can be promoted only when the redox potential of the additives reached a value between this range.(4) The optimized synthetic conditons are as following:DPPF-PdCl2were used as the catalysts,30mL methylene chloride as solvent, inorganic promoter CuCl20.75mmol, organic promoter benzoquinone (BQ)0.375mmol,2.5g tetrabutyl ammonium bromide as phase transfer catalyst, the total reaction pressure is5MPa (p(CO):p(O2)=93:7) the reaction temperature was110℃and the reaction time was3hours. The reaction conversion (TON) could reach69.5DPC mol/Pdmol.