DIRECT SPECTROSCOPIC DETECTION OF SULFONYLOXYL RADICALS AND 1ST MEASUREMENTS OF THEIR ABSOLUTE REACTIVITIES

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 λmax ∼ 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, kH ∼ 1.6 × 105 M-1 s-1, kH/kD ∼ 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 sulfonyloxyl radicals, a result that contrasts with that we have previously obtained for the decomposition of [Ph2P(=O)O]2, which yields radicals on photolysis but few if any radicals on thermolysis. Semiempirical AM1/PM3-UHF calculations on 2a are also reported. © 1990 American Chemical Society.