SYNTHESIS AND THERMAL-STABILITY OF SILICON-CONTAINING ESTERS OF PHOSPHORUS-ACIDS - 5 - THE RELATIVE MIGRATION ABILITY OF SUBSTITUENTS AT THE SILICON ATOM IN THE THERMAL REARRANGEMENT OF TRIALKYLSILYLMETHYL DIPHENYL PHOSPHATES

A number of trialkylsilylmethyl diphenyl phosphates MeRR'SiCH2OP(O)(OP h)(2) (1a-e: R = Et (a), Pr (b), CF3CH2CH2 (c, e), Me3SiCH2 (d); R' = Me (a-d), Et (e)) were synthesized and their thermal rearrangement, of the 1,2-shift type, was studied. The rearrangement consists of the mi gration of an alkyl group from Si atom to the methylene carbon atom an d gives the corresponding silyl esters. The rate of the rearrangement was found to increase in the order 1d < 1b < 1a < 1 (R = R' = Me) < 1c corresponding to the enhancement of the total inductive effect (-I) o f the substituents at the Si atom. The relative migration ability of t he substituents at the Si atom, determined by GC/MS analysis of the di siloxane fraction resulting from hydrolysis of pyrolyzed phosphates 1a -e, increases in the order R = Pr < Et < CF3CH2CH2 < Me much less than Me3SiCH2, which differs substantially from the order in which the rat e of the rearrangement of phosphates 1a-d changes. The electronegativi ty of the migrating group affects noticeably the relative ability to m igrate.