The cleavage of some silicon-carbon bonds.

An account of the cleavage of the silicon-carbon bond is given and relevant published work is reviewed including that on organosilicon rearrangements. A kinetic study using a spectrophotometric method has been made of the cleavage in aqueous-methanolic sodium hydroxide solution of the benzyl-silicon bond in twenty substituted benzyltrimethylsilanes, RC5H4CH2SiMe3. All of the substituents, R, were expected to withdraw electrons and all were found to facilitate the reaction relative to the unsubstituted compound. This is consistent with results of the few previous studies of this type of reaction and the mechanism proposed for it. The effects of substituents are discussed (in terms of electronic and steric effects) in series, such as all four halogens in ortho, meta and para positions and SO2X compounds (X = NH-, O-, NMe2, Ph). Discussion of this last series involves acceptance of the expansion of the octet of sulphur and a possible chelation between some of the X groups and the silicon atom when SO2X is ortho. Substituent effects are also considered in terms of linear free- energy relationships. A preparative procedure for the rearrangement in solution of chloromethyltriorganosilanes with aluminium ohloride has been developed. The scope of this rearrangement is indicated and a kinetic study was attempted. The latter study indicates that the rate of rearrangement is probably first-order with respect to the silane but is too complicated for an accurate study. Some other potential rearrangements were studied. During these investigations eighteen new organosilicon compounds were prepared.