Primary processes in the reaction of OH·-radicals with sulphoxides

Abstract

The primary processes in the OH* radical-induced oxidation mechanism of sulphoxides have been investigated by pulse radiolysis and, in particular, by an improved conductivity detection method with a time resolution of ca. 50 ns in aqueous solution. Electrophilic addition of the OH-radical to the sulphoxide group leads to a transient adduct, R,SO(OH). which decays unimolecularly with tl12 up to 100 ns into a sulphinic acid, RSO,H, and a radical R*.The various RS0,H have been identified by their pK, , and R* (including t-butyl and phenyl radicals) by direct optical measurement or chemical scavenging experiments. The probability of radical split-off from R,SO(OH)* for mixed sulphoxides depends on the stability of the radical leaving. Depending on the nature of the sulphoxide substituents two other OH* radical reactions compete with, and may even predominate over, the addition at the sulphoxide group. Thus hydrogen-atom abstraction readily occurs from longer chain and branched aliphatic groups and in the presence of aromatic substituents OH* radicals add to the n-system to form a hydroxycyclohexadienyl radical. The respective yields, kinetics and some physico-chemical properties of the primary species are presented and discussed.

Organic tanks safety program FY96 waste aging studies

“…Methyl radical liberated in the Equation 26 then attacks starting material to displace another 5-hexenyl radical (Equation 27). A reaction analogous to 27 in which HO* displaces methyl from DMSO is known to occur very rapidly (Veltwisch et al 1980). HO* + (CH3)2S=O + (CH3)2(0H)SO* + CH3* + CH3S02-+ H+ (28) As an alternative to a scheme involving Equations 19 to 22,26 and 27, we also considered that oximes might be derived from reaction with NO that is produced from photolysis of nitrite.…”

Mechanism of the Reaction of Radicals with Peroxides and Dimethyl Sulfoxide in Aqueous Solution

“…As expected, N 2 O-saturated solutions containing DMSO only result in the production of methane and ethane. [27,28] The relative yields of methane and ethane depend on the concentration of DMSO and the dose rate, as these gases are formed by reactions (1) and (10).…”

“…Especially, the plausible role of HCO 4 radicals, whereas methane is formed by the abstraction of hydrogen atoms from DMSO or methanesulfinic acid (CH 3 SOOH). [27,28] Recently, the rate constant of the reaction of methyl radicals with DMSO, thus contributing towards the formation of methane through abstraction of hydrogen atoms from the methyl group of DMSO, according to reaction (1), was reported.…”

“…[23] Indeed, the formation of methane or ethane (or final products of methyl radicals in aerated solutions) in DMSO-containing aqueous solutions is often taken as evidence that hydroxyl radicals were intermediates in the reaction mechanism and, therefore, DMSO is used as a probe for hydroxyl radicals. [24][25][26] Although DMSO is widely used to generate methyl radicals in dilute aqueous solutions by radiation or Fenton chemistry, its interactions with other radicals, which might be formed in the solution, was not fully studied.…”

Photohydroxylation of 1,4‐Benzoquinone in Aqueous Solution Revisited

“…The lack of radical products also excludes an efficient electron transfer, that is, the formation of QC À and a DMSO radical cation. The latter would be expected to react with water yielding the COH adduct, which has been shown [85] to give rise to methanesulfinic acid and a methyl radical. Methanesulfinic acid (or its oxidation product methanesulfonic acid) is not formed, not even in low yields (F < 0.03).…”