Synthesis Of Diphenyl Oxalate From The Transesterification Over Molybdenum-titanium Solid Acid Catalysts

Diphenyl carbonate (DPC) is an important organic material for non-phosgene production of polycarbonates (PCs), which has been extensively applied with good performance in mechanics, optics and electronics. Much attention has been paid to the synthesis of DPC. And the transesterification of dimethyl oxalate (DMO) with phenol to diphenyl oxalate (DPO) followed by decarbonylation of DPO to DPC is a promising route. This paper disscused the process of methyl phenyl oxalate (MPO) and DPO synthesis from the transesterification of DMO with phenol, and focused on the catalytic activities of the molybdenum-titanium solid acid catalysts in the transesterification reactions.It was indicated that the catalytic activity of MoO₃-TiO₂ compound catalyst prepared by sol-gel method was better than the MoO₃/TiO₂ supported catalyst. The results of BET, XRD, XPS, FT-IR showed that the compound catalyst had a fine compatibility of heterogeneous components, in which MoO₃ and TiO₂ dispersed evenly with the Mo-O-Ti bond formed. The dispersion of MoO₃ on the surface of TiO₂ accorded with the theory of monolayer. The MoO₃-TiO₂ catalyst performed the best activity near the threshold of dispersed MoO₃ corresponds to a saturated monolayer. Especially, the disproportionation of MPO into DPO was accelerated and the selectivity to DPO was improved. When the crystal MoO₃ was formed, the activity of catalysts and the selectivity to DPO were both decreased.The catalytic activity of solid superacid SO₄^2-/TiO₂ was inspected. The characterization of XRD, XPS, FT-IR, NH3-TPD indicated that the modification of SO₄^2- could inhibit the crystallization of TiO₂ during calcinations and provide a fine pore structure. As a result, the specific surface area of catalyst was highly increased. SO₄^2- coordinated with Ti4 + and the super acid centre created owing to the strong electronic induced effects caused by S=O.By means of BET, XRD, NH3-TPD, the excellent performance of SO₄^2-/MoO₃-TiO₂ during the transesterification of DMO with phenol was related with the modification of SO₄^2-. Supported with SO₄^2-, the specific surface area of MoO₃-TiO₂ catalyst was increased evidently, and the quantity of acid site was also increased. The catalyst of SO₄^2-/MoO₃-TiO₂ with 1% MoO₃ performed best, giving 64.16% conversion of DMO, 14.31% and 43.38% yield of DPO and MPO respectively.