Hydrogen disulfide radicals

At pH > 10.3, the concentration of RSH relative to RS is small and reaction 4, the hydrogen atom abstraction from RSH by the methylene blue derived radical MB, is a rate limiting factor. If reaction 4, along with the disulfide radical anion formation in reaction 2, are the rate limiting steps in the chain sequence, the reaction would follow the derived rate law shown in Eq. 12. Note that, in terms of the measurable kinetic... 

The effects of pH, ionic strength, reagent concentration ratios and deuterium substitution of the sulfur-bonded hydrogens on both the rates and rate laws for the methylene blue oxidations of mercaptoethanol and dithioerythritol have been determined. A free radical chain mechanism consistent with the observed kinetic behavior of the oxidation reactions is proposed. A key feature of the proposed mechanism is the formation of the sulfur-sulfur linkage of the disulfide in the reversible formation of a disulfide radical anion (RSSR) as a chain propagating step in the chain sequence. 

Treatment of 2-methylthiirane with t-butyl hydroperoxide at 150 °C in a sealed vessel gave very low yields of allyl disulfide, 2-propenethiol and thioacetone. The allyl derivatives may be derived from abstraction of a hydrogen atom from the methyl group followed by ring opening to the allylthio radical. Percarbonate derivatives of 2-hydroxymethylthiirane decompose via a free radical pathway to tar. Acrylate esters of 2-hydroxymethylthiirane undergo free radical polymerization through the double bond. 

It has been proposed that aromatic solvents, carbon disulfide, and sulfur dioxide form a complex with atomic chlorine and that this substantially modifies both its overall reactivity and the specificity of its reactions.126 For example, in reactions of Cl with aliphatic hydrocarbons, there is a dramatic increase in Ihe specificity for abstraction of tertiary or secondary over primary hydrogens in benzene as opposed to aliphatic solvents. At the same time, the overall rate constant for abstraction is reduced by up to two orders of magnitude in the aromatic solvent.1"6 The exact nature of the complex responsible for this effect, whether a ji-coinplex (24) or a chlorocyclohexadienyl radical (25), is not yet resolved.126- 22... 

The formation of dimethyl sulfide, dimethyl sulfone, and methane (by H-abstraction) observed in these photolyses is thus accounted for. Hydrogen abstraction by the methylsulfinyl radical affords methanesulfenic acid, CH3SOH, a very reactive molecule, which rapidly undergoes a series of secondary reactions to produce the methanesulfonic acid, methyl methanethiolsulfonate (CH3S02SCH3), and dimethyl disulfide which were also observed during these photolyses. 

Thiyl radicals from irradiated bis(2,2 -carboxyphenyl) disulfide failed to abstract hydrogen from acetic acid or an electron from acetate ion,... 

Irradiation of aliphatic thiols, sulfides, and disulfides with a mercury lamp produces gaseous products identified by the mass spectrograph. Thiols are the least stable to light, with the formation of hydrogen95-129 as the main product. Sulfides and disulfides yield, as the predominant products, saturated hydrocarbons of structures corresponding to the smallest alkyl radical attached to sulfur. Haines et al.95-97 have offered a mechanism to explain the predominant production of hydrogen during photolysis of thiols. 

Photolysis of aryl-desyl sulfides (LV, It = C H6) yielded didesyl (LVII).240 Desylthiobe n zoate (LV, R = SCOC6H6) gave didesyl and dibenzoyl disulfide. It is probable that in the former case the phenylthiyl radical (C0H6S ) abstracts hydrogen from the solvent to give thio-phenol and that in the latter reaction dibenzoyl disulfide is formed from the dimerization of benzoylthiyl radical (C H6COS-). The formation of LVII may be attributed to the dimerization of the desyl radical (LVI). O OH... 

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