Synthesis Of Diphenyl Carbonate By The Chemical Fixation Of Carbon Dioxide

Much attention has specially been paid to the utilization of CO₂ as the emission of it into the atmosphere increases. CO₂ is not only a greenhouse gas but also the most abundant carbon resource in the world. Chemical fixation of CO₂ to synthesize carbonates is one of the most effective means for producing the useful organic chemicals.Direct synthesis of diphenyl carbonate (DPC) from phenol and CO₂ in the presence of zinc halides and CCl₄ was studied in detail in this paper. The results showed that ZnCl2 revealed excellent catalytic performance for the reaction when it was used alone, and 25% yield of DPC was obtained at 8 MPa and 140℃f or 6 h. K₂CO₃ revealed significant effect on the conversion of phenol, the selectivity to and the yield of DPC. A larger selectivity to DPC but poorer conversion of phenol and yield of DPC was obtained. So the procedure was simplified without employing K₂CO₃.Direct synthesis of DPC from phenol and compressed CO₂ in the presence of ZnCl2 and CCl₄ was also studied, in which compressed CO₂ was used as reagent as well as solvent. The effect of Lewis catalyst, reaction temperature, amount of CCl₄, reaction pressure and reaction time was investigated. The results showed that zinc halides exhibited higher catalytic activity than that of aluminum halides, but Lewis acid with the identical metal center revealed negligible effect on the catalysis. Almost the similar selectivity to and the yield of DPC were obtained under relative mild conditions at 9 MPa and 100℃for 2 h compared to that was obtained with CCl₄ employed as solvent at 8 MPa and 140℃for 6 h. Apparent drop was observed both in the reaction temperature and the reaction time with compressed CO₂ as reaction medium.The addition of ionic liquid and ligand containing nitrogen revealed negative effect on the selectivity to and the yield of DPC although the conversion of phenol was significantly enlarged. Both the conversion of phenol and the yield of DPC were promoted by using triethylamine as acid acceptor, the yield of DPC increased from 21 to 25%.The products from CO₂ and phenol to DPC with different catalytic systems were identified by GC-MS analysis. The results showed that the distribution of products was depended on K₂CO₃. Only DPC and main by-product phenyl salycilate were observed in the liquid reaction mixture in the presence of K₂CO₃. However, another by-product chloroformic acid phenyl ester was also observed in the absence of K₂CO₃. A possible mechanism for the direct synthesis of DPC from CO₂ and phenol in the presence of CCl₄ catalyzed by ZnCl2 was proposed on the basis of GC-MS analysis.