Study On The Synthesis Of Diphenyl Carbonate By The Oxidative Carbonylation Of Phenol Over PdCl₂

Diphenyl carbonate (DPC), as an important organic carbonate, is an important precursor for producing polycarbonates(PC) by a melt-polymerization process. Oxidative carbonylation of phenol to synthesize DPC is an one-step synthetic method. This paper focuses on the synthesis of diphenyl carbonate through oxidative carbonylation of phenol over homogeneous catalyst PdCl2.The optimum reaction condition was 80℃, 2.5MPa, molar ratio of CO:O2=4:1 and 6h, and Ce(OAc)3 was found to be the best organic cocatalyst. In addition, the role of molecular sieve(M.S.)and solvent has been investigated by experiments.It could be concluded that 3.0g 3A 40-60mesh M.S. was the most efficient dehydrating agent and chlorobenzene was the most suitable solvent. Both of them could increase the conversion of phenol and DPC yield. At the optimum condition, phenol conversion and DPC yield could be up to 20.4% and 15.6%.It has been proved that by-product water had a significant influence on the synthesis of diphenyl carbonate through oxidative carbonylation of phenol. When water content exceeded 1.49wt.%, DPC yield descended rapidly for a large amount of by-products being produced.The influence of water on the reactants, products and catalyst has been also investigated. The results showed that CO water-gas-shift was the main route to form by-product CO2. What's more, CO2 could react with phenol to produce salicylic acid, which would result in producing the main product phenyl salicylate(PS) through further esterifying with phenol. In the DPC hydrolysis experiments, it could be concluded that DPC hydrolysis will not descend DPC yield dramatically. According to XPS results of PdCl2 after reaciton, there are 81.18% Pd(Ⅱ) being reduced to Pd(0), indicating that the redox recycle of Pd(0) to Pd(Ⅱ) was hindered and Pd(0) accumulated because of the existence of water, which will lead to the decline in catalytical activity.