One-Electron Reduction of Methanesulfonyl Chloride. The Fate of MeSO₂Cl^•- and MeSO₂^• Intermediates in Oxygenated Solutions and Their Role in the Cis−Trans Isomerization of Mono-unsaturated Fatty Acids

Abstract

The one-electron reduction of methanesulfonyl chloride (MeSO2Cl) leads, in the first instance, to an electron adduct MeSO2Cl(.)(-) which lives long enough for direct detection and decays into sulfonyl radicals MeSO2(.) and Cl(-), with k = 1.5 x 10(6) s(-1). Both, MeSO2Cl(.)(-) and MeSO2(.) showed a similar absorption in the UV with lambdamax of 320 nm. In the presence of oxygen, MeSO2Cl(.)(-) transfers an electron to O(2) and establishes an equilibrium with superoxide. The rate constant for the forward reaction was measured to 4.1 x 10(9) M(-1) s(-1), while for the back reaction only an interval of 1.7 x 10(5) to 1.7 x 10(6) M(-1) s(-1) could be estimated, with a somewhat higher degree of confidence for the lower value. This corresponds to an equilibrium constant in the range of 2.4 x 10(3) to 2.4 x 10(4). With reference to E degrees (O2/O2(.)(-)) = -155 mV, the redox potential of the sulfonyl chloride couple, E degrees (MeSO2Cl/MeSO2Cl(.)(-)), thus results between being equal to -355 and -414 mV (vs NHE). MeSO2Cl(.)(-) reduces (besides O2) 4-nitroacetophenone. The underlying electron transfer took place with k = 1.5 x 10(9) M(-1) s(-1), corroborating an E degrees for the sulfonyl chloride couple significantly exceeding the above listed lower value. The MeSO2(.) radical added to oxygen with a rate constant of 1.1 x 10(9) M(-1) s(-1). Re-dissociation of O2 from MeSO2OO(.) occurred only very slowly, if at all, that is, with k << 10(5) s(-1). MeSO2(.) radicals can act as the catalyst for the cis-trans isomerization of several Z- and E-mono-unsaturated fatty acid methyl esters in homogeneous solution. The effectiveness of the isomerization processes has been addressed, and in the presence of oxygen the isomerization is completely suppressed.

The hydrogen atom transfer reactivity of sulfinic acids

“…The rate constant for the reaction of sulfonyl radicals with O 2 has been reported to be 1 × 10 9 M –1 s –1 in water/MeOH. 61 If the reaction were this fast in organic solvent, reactions involving sulfonyl radicals would be impossible under aerobic conditions. 12 , 13 , 17 For example, under the reaction conditions developed by the Lei group for oxidative functionalization of alkynes, 13 both the addition of sulfonyl radicals and the addition of oxygen would have effective rates of around 1 × 10 7 s –1 .…”

Diastereo- and Enantioselective Catalytic Radical Oxysulfonylation of Alkenes in β,γ-Unsaturated Ketoximes

“…Obvious E-Z isomerization occurred as the reactions started, indicating fast, reversible addition of sulfonyl radicals to alkenes as reported in literature. [49][50][51][52][53] Most importantly, both (E)-and (Z)-5a afforded (5R,2'S)-6aa with the same absolute configuration as the major product. The results strongly support the involvement of the same rate-and stereo-determining C-O bond formation step for reactions on both (E)-and (Z)-5a.…”

“…The addition of sulfonyl radicals (RSO 2 ,) to alkenes is known to be fast and reversible. [49][50][51][52][53] Accordingly, we hypothesized that a scenario under Curtin-Hammett kinetic control 54,55 might be achieved via a rapid equilibrium between the initial addition diastereomers C and D (Scheme 1B). Subsequent rate-determining asymmetric functionalization of these alkyl radicals might deliver the desirable product (e.g., P C ) with excellent control of both enantioselectivity and diastereoselectivity.…”

Thiyl Radical Reactions in the Chemical Degradation of Pharmaceutical Proteins

“…Thiyl radicals reversibly add oxygen to yield thiylperoxyl radicals (RSOO • ) (Reaction (5)) [54]. The latter can rearrange to sulfonyl radicals (RS • O 2 ) (Reaction (6)) [54] and further convert into sulfonylperoxyl radicals (RSO 2 OO • ) (Reaction (7)) [55]. In the presence of electron or hydrogen donors, sulfonyl radicals convert into sulfonates, while sulfonylperoxyl radicals ultimately yield sulfonates [56,57].…”