| Résumé | The reactions of the phosphoranyl radicals formed by the addition of tert-butoxy radicals to trimethyl, triethyl, triisopropyl, and tri-tert-butyl phosphite have been examined by epr spectroscopy. At temperatures below ca. -115° the t-BuOṖ(OMe)3 and t-BuOṖ(OEt)3 decay with second-order kinetics. At higher temperatures all four radicals decay with first-order kinetics to yield phosphate and a tert-butyl radical. The rates of this β-scission reaction increase by about an order of magnitude at -60° along the series from t-BuOṖ(OMe)3 to to (t-BuO)4P. Arrhenius parameters for β-scission have been determined by kinetic epr spectroscopy and by a competitive procedure. The latter method has shown that tert-butyl radicals react with phosphoranyl radicals with rate constants that are approximately the geometric mean of the rate constants for the bimolecular self-reactions of the tert-butyl and phosphoranyl radicals. The mechanism of β-scission is discussed. |
|---|
