Catalytic Reaction System On The Chemical Conversion Of Carbon Dioxide Into Diphenyl Carbonate

The concentration of carbon dioxide (CO2) in the atmosphere is increasingwith the consumption of traditional fossil fuel such as coal and oil, resulting in“greenhouse effect” and serious effect on the ecological balance and environmentalsystem. In fact, CO2can be converted into organic carbonate via chemicalconversion because it is not only a greenhouse gas but also the greatest carbonresource in the world, which is significant in exploiting natural resource andprotecting environment. Diphenyl carbonate (DPC) is an important organiccarbonate and widely used in modern chemical industry, and the development ofgreen technology to synthesize polycarbonate from DPC and bisphenol A leading toan increase in demand of DPC. Therefore, the development of direct synthesis ofDPC from CO2and phenol has a prosperous application.The simple Lewis acid zinc chloride (ZnCl2) revealed excellent catalyticperformance in the synthesis of DPC from CO2, phenol and carbon tetrachloride(CCl4), and24%yield of and39%selectivity to DPC was obtained at120oC and9MPa for6h with0.5molar ratio of ZnCl2to phenol, respectively. The co-catalyticperformance of tetrabutylammonium bromide, potassium carbonate, cesiumcarbonate and organic Br nsted acid trifluoromethanesulfonic acid (CF3SO3H) inthe synthesis of DPC was also investigated. It was found that the catalytic activityof ZnCl2was obviously enhanced by the addition of CF3SO3H but not in thepresence of common bases. An efficient catalytic system of ZnCl2-CF3SO3H wasexplored via the optimization of the molar ratio and reaction conditions, and22%yield and56%selectivity to DPC was obtained at130oC and8MPa for6h with0.5:1:10molar ratio of CF3SO3H, ZnCl2and phenol, respectively.A novel and green method to synthesize DPC from CO2, phenol and CH3OHwas developed, in which CCl4was replaced by CH3OH. The catalytic performanceof zinc halide and aluminum halide (AlBr3) was studied, and the results showed thataluminum bromide revealed the most excellent catalytic activity among the selectedsimple Lewis acids. The influence of the amount of AlBr3and the reactionconditions was optimized, and7.1%yield of DPC was obtained at90oC and8MPafor2h with0.3molar ratio of AlBr3to phenol.The products in the reaction mixture from CO2and phenol in the presence ofCCl4or CH3OH were identified by GC-MS analysis. The GC-MS analysis of thecrude product from CO2, phenol and CCl4catalyzed by ZnCl2-CF3SO3H confirmedthat the synthesis of DPC is accompanied by the formation of phenyl salicylate, anda possible mechanism was proposed based on the GC-MS results. Besides DPC andmethyl phenyl carbonate, a small amount of3-bromophenol and4-bromophenol were also detected by GC-MS in the liquid product from CO2, phenol and CH3OHcatalyzed by AlBr3and the possible reaction pathway of this reaction system wasobtained by thermodynamic calculation using density functional theory (DFT). Apossible mechanism for the formation of DPC from CO2, phenol and CH3OH wasthen proposed based on the GC-MS analysis and DFT calculation.