Thiosulphinates oxidation

Thiosulphinates are derivatives of disulphides with one of the sulphur atoms at the sulphoxide oxidation level. In theory, oxidation of a thiosulphinate could produce two products, a disulphoxide and a thiosulphonate (equation 79). Discussions of this topic have been very polarised over the years but now it is fairly well established that the thiosulphonate is the major product formed in most cases, although the intermediacy of a a-disulphoxides is indicated from some data. 

The reaction mechanism for the peracid oxidation of thiosulphinates is perhaps more complex than described above. A study of the low-temperature ( — 40 °C) peracetic acid oxidation of 2-methyl-2-propyl 2-methyl-2-propanethiosulphinate gave two products as shown in equation (81)196. During the reaction the a-disulphoxide was apparently detected by NMR spectroscopy. 

Unsymmetrical thiosulphinates and thiosulphonates are both oxidized by potassium superoxide in pyridine in the presence of 18-crown-6 ether to produce sulphinic and sulphonic acids and a disulphide, under mild conditions (equation 84)200,201. Sulphinic and sulphonic acids were produced from both the R and R substituents whilst the disulphide was derived only from the sulphenyl side of the reactant. Thus, the reaction mixture contained five products, making the reaction not synthetically useful. Pyrolysis of thiosulphinates also produces mixtures of products, one being the thiosulphonate again this is not a synthetically useful reaction202. 

Electrochemical oxidation of thiosulphinates leads cleanly to the corresponding thiosulphonate in reasonable yields with no observed side-products203. 

Oxidation of aromatic thiols with nitrogen dioxide leads to a variety of products, depending on the reaction conditions5,219,220. If the reaction is carried out at 25 °C in carbon tetrachloride using six equivalents of the oxidizing agent, then a quantitative yield of the aromatic sulphonic acid is formed, as depicted in equation 33. The reaction proceeds via the disulphide and the thiosulphinate, both of which may be isolated if the reaction is carried out at lower temperatures. 

Some products of interaction of tert-BuOOH with thiobisphenol CLXVIIIa were probably formed according to these general reactions. From the reaction mixture, these were isolated272 4,4 -sulphinylbis(2-methyl-6-tert-butylphenol) CLXXXIIa and 4,4 -sulphonylbis(2-methyl-6-tert-butylphenol) CLXXXIIIa. 4-[(3-Methyl-5-tert-butyl-4-hydroxyphenylthio)-sulphonyl]-2-methyl-6-tert-butylphenol CLXXXVa is derived from dithiobisphenol CLXXIXa which belongs to primary products of transformation. The thiosulphinate CLXXXIVa which is less stable to thermal decomposition and oxidation is assumed as an intermediate. 

Oxidation of thiols or disulphides in pyridine solution in the presence of ADP and inorganic phosphate by two equivalents of iodine or bromine leads to the formation of ATP. The initial reaction between the disulphide and positive halogen is presumably followed by the displacement of halide by phosphate ion to give a phosphorylating species (52). ADP would react with (52) with the formation of ATP and a thiosulphinic... 

Freeman, G. Whenham, H. (1976) Thiopropanal S-oxide, alk(en)yl thiosulphinates and thiosulphonates simulation of flavour components of Aiiium species. Phytochemistry 15, 187-190. 

S—S— Oxidations. As shown in the above scheme, the oxidation of disulphides can lead to a variety of compound types. In the earlier ones, the —S—S— bond is preserved, whereas further oxidation leads to the mono-sulphur products, sulphinic and sulphonic acids. For asymmetric disulphides, the point of first oxidation to monosulphoxide (thiosulphinate) is adjacent to the more electron-donating substituent. This is usually carried out by peracid systems at or below ambient tern-... 

Figure 2.7 (a) Degradation of 1-propenyl-L-cysteine in onions to cycloalliin, propanethial S-oxide (the major lacrimatory compound derived from onions), and to an unstable thiosulphinate which further degrades (see Figure 2.8). (b) Degradation of 2-propenyl-L-cysteine in garlic, which lacks LF synthase. 

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