Ring-Opening Reaction of Hexamethylcyclotrisiloxane with Tetrachlorosilane and Isomerization of the Product

摘要

A molecular complex of triphenylphosphine oxide and tetrachlorosilane (II) in a solvent mixture that contains 90% toluene and 10% acetonitrile acts as a catalyst to open the cyclic siloxane oligomer, hexamethylcyclotrisiloxane (I). The primary product is the linear oligomer 1, 1, 1, 7-tetrachlorohexamethyltetrasiloxane (III). III can be converted quantitatively to th structural isomer, 1, 3, 3, 7-tetrachlorohexamethyltetrasiloxane (IV), in the same catalyst-solvent mixture either by stirring at room temperature for 12 h or by heating at 90 deg C for about 1 h. In both reactions, the disappearance of the reactants and the formation of the products can be followed by glc. Products III and IV are characterized by elemental analysis, molecular mass, infrared spectra, and ~1H- and ~(29)Si-NMR spectra. III and IV can be transformed into their fluorinated derivatives, VI and VII, respectively, by stirring for several days in a toluene slurry of KSiF_6. The ~(19)F-NMR spectra of VI and VII are consistent with the proposed isomeric structures.