And oxidation of thiols

Oxidation of sulfides to sulfoxides and oxidation of thiols to disulfides... 

The TFE- or HFIP-activated H2O2 oxidant promotes not only epoxidation [34, 47, 48], but also Baeyer-Villiger oxidation [48], oxidation of sulfides to sulfoxide [34, 49], and oxidation of thiols to disulfides [5, 50]. The nature of the weaker nucleophilicity and higher acidity of TFE as compared with ethanol is useful as a solvent for Pd-catalyzed asymmetric hydrogenation of trifluoromethylimines [51]. 

Salgo, M.G., Bermudez, E., Squadrito, G.L. and Pryor, W.A. 1995. Peroxynitrite causes DNA damage and oxidation of thiols in rat thymocytes. Arch. Biochem. Biophys 322 500-505. 

A major difference between alcohols and thiols concerns their oxidation We have seen earlier m this chapter that oxidation of alcohols gives compounds having carbonyl groups Analogous oxidation of thiols to compounds with C=S functions does not occur Only sulfur is oxidized not carbon and compounds containing sulfur m various oxida tion states are possible These include a series of acids classified as sulfemc sulfimc and sulfonic according to the number of oxygens attached to sulfur... 

Disulfides. As shown in Figure 4, the and h-chains of insulin are connected by two disulfide bridges and there is an intrachain cycHc disulfide link on the -chain (see Insulin and other antidiabetic drugs). Vasopressin [9034-50-8] and oxytocin [50-56-6] also contain disulfide links (48). Oxidation of thiols to disulfides and reduction of the latter back to thiols are quite common and important in biological systems, eg, cysteine to cystine or reduced Hpoic acid to oxidized Hpoic acid. Many enzymes depend on free SH groups for activation—deactivation reactions. The oxidation—reduction of glutathione (Glu-Cys-Gly) depends on the sulfhydryl group from cysteine. 

Gas-phase oxidation of thiols has been discussed in some depth (33). This review mainly emphasi2es atmospheric processes, but a section on nitrogen oxides and thiols appears to be broadly appHcable. The atmospheric oxidation chemistry of thiols is quite different from that of alcohols. 

Alkyl sulfonic acids are prepared by the oxidation of thiols (36,37). This reaction is not quite as simple as would initially appear, because the reaction does not readily go to completion. The use of strong oxidants can result in the complete oxidation of the thiol to carbon dioxide, water, and sulfur dioxide. 

Although the oxidation of thiols with chlorine or bromine in the presence of water gives sulfonyl halides or sulfonic acids, the reaction of thiols with a stoichiometric amount of BTMA Br3 and sodium hydroxide in dichloromethane-water at room temperature gives disulfides in good yields (Fig. 29) (ref. 37). 

A particular interest for clinical applications was a possibility for detection of dopamine by its oxidation on nickel [19], cobalt [65], and osmium [66] hexacyanofer-ates. Except for oxidation of dopamine, cobalt and osmium hexacyanoferrates were active in oxidation of epinephrine and norepinephrine. For clinical analysis it is also important to carry out the detection of morphine on cobalt [67] and ferric [68] hexacyanoferrates, as well as the detection of oxidizable amino acids (cystein, methionine) by manganous [69] and ruthenium [70] hexacyanoferrate-modified electrodes. In general, oxidation of thiols was first shown for Prussian blue [71] and nickel hexacyanoferrate [72], This approach has been used for the detection of thiols in rat striatum microdialysate [73], Alternatively, the detection of thiocholine with Prussian blue was employed for pesticide determination in acetylcholine-esterase test [74],... 

Regeneration of superoxide during the oxidation of thiols hints at the possible prooxidant effect of these antioxidants. This suggestion was recently confirmed by Mottley and Mason [212] who have showed that superoxide was formed in the oxidation of DHLA by horseradish peroxidase in the presence of phenol. However, DHLA is dithiolic compound and the other mechanisms such as the concerted mechanism, which has been proposed earlier for flavonoids may be realized (Figure 29.6). 

The conversion (19) of thiols to disulphides coupled with reduction of flavin (vitamin B2 family) is a topic of import in connection with coenzyme reactivity in flavoenzymes. Since flavin oxidation of thiols involves nucleophilic attack of thiolate ion in the rate-determining step (Loechler and Hollocher, 1975 Yokoe and Bruice, 1975), this biologically important reaction would be markedly affected by hydrophobic environments. 

Oxidation of thiols and related compounds with organoselenium(IV) and organotellurium(rV) compounds 102 Other oxidations with selenoxides and telluroxides 106 Thiolperoxidase and haloperoxidase-like activity of organoselenides and organotellurides 108... 

OXIDATION OF THIOLS AND RELATED COMPOUNDS WITH ORGANOSELENIUM(IV) AND ORGANOTELLURIUM(IV) COMPOUNDS... 

Selenoxides and telluroxides also function as mild oxidants for the conversion of thiols to disulfides as shown in equations (16) and (17) for the reaction of thiophenol with diphenylselenoxide (47) and diphenyltelluroxide (48). Mechanistically, the oxidation of thiols to disulfides with selenoxides and telluroxides is a multi-step process, which takes advantage of the ease with which tellurium(IV) and selenium(IV) species form trigonal bipryamidal... 

Diorgano diselenides have been used extensively as precursors to seleninic acids in the presence of hydrogen peroxide.The catalytic activity of preformed seleninic acids and seleninic acids generated in situ are identical. Diorgano ditellurides have also been used as catalysts in thiolperoxidase-like reactions for the oxidation of thiols with various peroxides. However, tellurinic acids are not thought to be involved even though RTe(=0)SPh types of structures are proposed as intermediates. 

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