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[摘要]：A time-resolved kinetic study on the reactions of alkoxyl radicals with trialkyl and triaryl phosphites ((RO)(3)P: R = Me, Et, i-Pr, t-Bu; (ArO)(3)P: Ar = C6H5, 2,4-(t-Bu)(2)C6H3) has been carried out. In the (RO)(3)P series, the alkoxyl radicals (cumyloxyl (CumO(center dot)) and benzyloxyl (BnO center dot)) undergo addition to the phosphorus center with formation of intermediate tetraalkoxyphosphoranyl radicals (R'OP center dot(OR)(3): R = Me, Et, i-Pr, t-Bu; R' = Bn, Cum). The addition rate constants are influenced by steric effects, decreasing on going from R = Me to R = t-Bu and from BnO center dot to CumO(center dot). Rate constants for beta-scission of the phosphoranyl radicals R'OP center dot(OR)(3) have also been determined, increasing, for a given alkyl group R, in the order R' = tert-butyl < R' = benzyl < R' = cumyl and, for a given R' group, on going from R = Me to R = i-Pr. This behavior has been explained in terms of the relative stability of the radicals formed after beta-scission, suggesting moreover that steric effects play in this case a minor role. CumO(center dot) reacts with triaryl phosphites (ArO)(3)P to give phenoxyl radicals, with rate constants that are influenced to a limited extent by substitution of the aromatic rings. The radical scavenging ability of these substrates is briefly discussed. |
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