Direct Spectroscopic Detection of Sulfonyloxy Radicals and First Measurements of Their Absolute Reactivities

Article abstract of DOI:10.1021/j100388a017

Two sulfonyloxyl radicals, CH3S(=O)2O^., 2a, and 3-CF3C6H4S(=O)2O^., 2b, have been generated by 308-nm laser flash photolysis (LFP) of their parent symmetrical peroxides in CH3CN solution, in which they have lifetimes of 7-20 μs.Both radicals exhibit a broad, structureless absorption similar to that known for SO4^.- with λ_max ca. 450 nm.This absorption can be bleached for 2a but not for 2b by firing a second laser at 480 nm, presumably reflecting a photoinduced cleavage of the H3C-SO3^. bond.Radicals 2a and 2b react with the acetonitrile solvent by abstraction of a hydrogen atom, k_H ca. 1.6*10⁵ M^-1 s^-1, k_H/k_D ca. 2.0.Bimolecular rate constants for attack of these radicals on cyclohexane (viz., 1.9*10⁸ and 6.5*10⁸ M^-1 s^-1 for 2a and 2b, respectively) and chloroform (viz. ca., 3*10⁵ M^-1 s^-1 for both) demonstrate that they are more reactive than almost all other oxygen-centered radicals.Product studies demonstrate that both the photodecomposition and the thermal decomposition of the parent peroxides yield the corresponding sulfonyloxy radicals, a result that contrasts with that we have previously obtained for the decomposition of 2, which yields radicals on photolysis but few if any radicals on thermolysis.Semiempirical AM1/PM3-UHF calculations on 2a are also reported.