Oxidation to sulfonic acids

Thiols, sulfoxides, sulfones, disulfides,407 and other sulfur compounds can be oxidized to sulfonic acids with many oxidizing agents, though for synthetic purposes the reaction is most important for thiols.408 Among oxidizing agents used are boiling nitric acid and barium... 

For a general review of Ihe oxidation of thiols, see Capozzi Modena, in Patai The Chemistry of the Thiol Group. pt. 2 Wiley New York, 1974, pp. 785-839. For a review specifically on the oxidation to sulfonic acids, sec Gilbert Sulfonation and Related Reactions Wiley New York. 1965, pp. 217-239. 

Sulfonation of benzo[6 ]thiophene with concentrated sulfuric acid in acetic anhydride at 20 °C gives a mixture which is chiefly the 3-sulfonic acid, with some 2-isomer and 3-acetylbenzo[6 Jthiophene (70AHC(i)l77). Chlorosulfonation of 2- or 3-methyl-benzo[6 Jthiophene gives the corresponding 3- or 2-sulfonyl chloride in satisfactory yield. The various available 4-, 5-, 6- and 7-mercaptobenzothiophenes or sulfides (Section 3.15.9.5.2) can be oxidized to sulfonic acids or sulfones by conventional means. 

Disulfides have been oxidized to sulfonic acids with hydrogen peroxide in the presence of tungstic acid.401 Whilst sulfonic acids are the normal oxidation product, intermediates of the structure RSS(0)R have been isolated.402... 

It has been estimated that the reverse of the above equilibrium is favored by 106 for R = aryl, and to an even greater extent for R — alkyl (4). However, in the presenoe of hydroperoxide sulfenic acid would be readily oxidized to sulfonic acid, a catalytic peroxide decomposer (I). 

Thiols can be oxidized to sulfonic acids by stronger oxidizing agents. This method is generally applicable and has often been used for preparation of specific sulfonic acids. Nitric acid583,584 or potassium permanganate585... 

Disulfides can be oxidized to sulfonic acids in the same way as thiols 589-593... 

S.Sulfur is expected to be oxidized to sulfonic acid, undergo alkylation and conjugation and be excreted. 

A number of substances in this group contain a thiol group, which is predicted to be metabolized by methylation followed by oxidation, conjugation with GSH, S-glucuronidation and/or oxidation to sulfonic acids. These would be the major routes... 

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