Rates of addition of phenylthio radicals to vinyl sulphide, sulphoxide, sulphone, and ether groups

Abstract

The rate constants for addition of para-substituted phenylthio radicals to vinyl sulphide, sulphoxide, sulphone, and ether groups have been determined by flash photolysis. The polar nature of the vinyl monomers was examined by constructing Hammett plots vs. σ⁺ of the substituents on the phenylthio radicals; the reaction constants (ρ⁺) are 2.0–2.2 for sulphides, 1.7–1.8 for ethers, 1.2 for sulphoxide, and 0.8 for sulphone, suggesting that the ρ⁺ value increased with the electron density of the double bond. For phenylthio radical, the rate constants (in dm³ mol^–1 s^–1) of the vinyl sulphides [(2.6–4.8)× 10⁶] are greater than those of the vinyl ethers [(0.8–1.0)× 10⁵], the sulphoxide (1.4 × 10⁴), and the sulphone (1.6 × 10⁴), suggesting that stabilization of the carbon-centred radical adduct is a characteristic of the adjacent sulphide group.