Thiosulfoxyl acid

We have thus established that sulfides, disulfides, and their initial oxidation products are not the actual preventive antioxidants. The active peroxide decomposers are the sulfenic acid from sulfoxide decomposition, the thiosulfoxylic acid from thiolsulfinate decomposition, and the acidic products formed when they react with hydroperoxides. The catalytic... 

Formation of the thiosulfoxylic acid intermediate has been demonstrated by mass spectroscopic studies and trapping experiments. The thiosulfoxylic acid formed may then react with hydroperoxide through a mech-nism that destroys many moles of hydroperoxide per mole of sulfur compound (I). 

Alternatively, the formation of thiosulfoxylic acid may be only the first in a series of consecutive reactions leading to the effective peroxide decomposing species. 

Initially the acid catalyst for Reaction 3 would be supplied by decomposition of the thiosulfinate to thiosulfoxylic acid as an induction period. 

The following reaction sequence is suggested. Initially the thiolsul-finate undergoes an intramolecular cycloelimination reaction as in Reaction 1. Extensive supporting evidence for this postulate has been presented by Block (4) from studies on the decomposition of thiolsulfinate under mild conditions (< 100°C). Since Reaction 1 is favored over homolysis and a reactive species, thiosulfoxylic acid, is formed, Reaction 1 is probably the initial step. 

The thiosulfoxylic acid may be expected to undergo oxidation to the corresponding thiosulfurous and thiosulfuric acid (2). 

The radicals generated may induce decomposition of the thiolsul-finate as proposed by Barnard and Percy (6). An alternative fate of generated radicals will be an attack on thiosulfoxylic acid ... 

This reaction is facilitated by formation of the stabilized RSSO radical that is isoelectronic with the stabilized polysulfide radical, RS3. The analogous sulfenic acids are effective radical scavengers reacting with peroxy radicals with a rate constant of KFM"1 sec1 at 60°C (16). The S-S bond in the thiolsulfinate is weak, and the corresponding bond in the thiosulfoxyl radical should be considerably less stable. Thus, the thiosulfoxyl radical may function as a source of sulfur oxides ... 

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