The transesterification mechanism of dimethyl carbonate with phenol to diphenyl carbonate (DPC) over di-n-butyltin oxide was studied. It has been found that both phenol and DPC could react with di-n-butyltin oxide to form an intermediate. Its crystal structure was determined by X-ray single crystal diffraction analysis. The crystal belongs to monoclinic system with space group P2₁/n. Its unit cell parameters are as follows: a＝1.3336(2) nm, b＝1.7208(2) nm, c＝1.3759(3) nm, β＝101.00(2)°, V＝3.0993(9) nm³, D_c＝1.432 g/cm³, Z＝4, F(000)＝1352, μ＝1.635 mm^－1. The identification results show that the intermediate is a novel dimeric tetraorganodistannoxane [Bu₂Sn(OPh)OSnBu₂O(Ph)]₂ (I), which has a layer structure with centric symmetry. The MS and XPS results demonstrate that I exists steadily in the reaction condition. A reasonable transesterification mechanism based on the experimental consequence was then offered in this paper.

Key words: dimethyl carbonate, diphenyl carbonate, transesterification mechanism, tetraorganodistannoxane, phenol