Interconversion of siloxanes

IEC 165

Alan R. Bassindale1, Peter G. Taylor1, Thomas H. Lane2, and Khristopher E. Alvarez2. (1) Department of Chemistry, Open University, Milton Keynes, England, (2) New Ventures, Dow Corning Corporation, Midland, MI 48686
In 1978 Frye et al. reported the interconversion of 2,6-trans-diphenylhexamethylcyclotetrasiloxane to an equal molar mixture of the cis and trans isomers of the cyclosiloxane. They reported that the interconversion occurred rapidly in the presence of a Lewis acid and a polar aprotic solvent. There was no reported production of other isomers or linear oligomers. This reaction appears to be highly selective. Frye proposed two possible reaction schemes, both involving breaking a Si-O bond and opening of the cyclic siloxane. However, we believe there are other, more plausible, explanations for this discovery. The mechanism of this interesting reaction and its potential utility will be discussed.