Seleninic acids diselenides

Excess of 30% H2O2 added to a soln. of 2,4,6-trimethylbenzaldehyde and a little bis(2,4-dinitrophenyl) diselenide in dichloromethane, stirred at room temp, for 28 h, the catalyst filtered off, the crude intermediate dissolved in methanol, a soln. of KOH in the same solvent added in 3-4 portions with water-cooling, and allowed to stand for at least 1 h at room temp. - 2,4,6-trimethylphenol. Y 91%. The method is particularly useful for substrates with 2 or more alkoxy groups or with alkyl groups, acid-sensitive substituents remaining intact. F.e. and with diselenides, seleninic acids, or Se02 as catalyst s. L. Syper, Synthesis 1989, 167-72. 

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. 

Iodine in the presence of sodium hydrogen carbonate converts diselenides quantitatively into seleninic acids ... 

Dibenzyl diselenide crystallises from alcohol in yellow needles, which are slightly deeper in colour than those of the p-nitrobenzyl compound, and melt at 92° to 93° C. Exposure to light for an hour or so causes the crystals to turn red. The selenide readily dissolves in hot alcohol, but is only sparingly soluble in ether, insoluble in water. Oxidation with fuming nitric acid converts it into benzyl seleninic acid, and boiling with copper or mercury in suspension precipitates selenium. Boiling with iodine in chloroform solution gives the tetra-iodide, M.pt. 98° C. the tetrabromide melts at 137° C.5... 

As shown in Scheme 1, the reduction of diselenides generates selenols and selenolates, while their oxidation results in the formation of selenenic and seleninic acids and related compounds (see Section 7). Halogenation of diselenides with... 

The partial oxidation of diselenides with appropriate oxidants such as hydrogen peroxide initially generates the corresponding selenenic acids (29) or anhydrides (28). Further oxidation leads to the corresponding seleninic acids (31) or... 

Oxidation of diselenides with Br2, H202,23s-23 HN03,2 -2 i ozone, 2 TBHP242-244 nd MCPBA affords seleninic acids (30) and/or their anhydrides (31 equation 40), both of which are known as useful oxidants of various organic compounds. The oxidation has been suggested to proceed as shown in Scheme 11 and as evidence intermediate compounds were isolated m the MCPBA oxidation of... 

Organic selenenic acids and their anhydrides are thermally unstable and readily disproportionate into the corresponding diselenides and seleninic acids (or their anhydrides) [15 a, 32]. Because this process is believed to be reversible, these selenium compounds can be generated in situ by the comproportionation, i.e. the reverse processes (going right to left in the following equations), and used directly without isolation (Scheme 15.10) [32-34]. 

Methods of synthesis of seleninic acids are based on oxidation of diselenides (or selenocyanates) with HNOj [38k, 42[ or H2O2 [23a, 42d, 43[. Seleninic anhydrides are prepared by dehydration of seleninic acids [42 e, 44[ or by oxidation of diselenides with ozone (Scheme 15.14) [44, 45]. 

Benzeneseleninic acid, CsHjSeOH Mol. wt. 189.07, m.p. 122-124". Diphenyl diselenide reacts with 3 moles of ozone to form benzeneseleninic anhydride, which reacts with water to form the seleninic acid. ... 

The catalysts applied to alkene epoxidation in fluorinated alcohol solvents can be subdivided into those which are metal/chalconide-based and those which are purely organic in nature (Scheme 4.5). The former comprise arsanes/arsane oxides [27,28], arsonic acids [29, 30], seleninic acids/diselenides ]31-35], and rhenium compounds such as Re207 and MTO (methylrhenium trioxide) ]36,37]. As shown in Scheme 4.5, their catalytic activity is ascribed to the intermediate formation of, for example, perseleninic/perarsonic adds or bisperoxorhenium complexes. In other words, their catalytic effect is due to the equilibrium transformation of hydrogen peroxide to kmetically more active peroxidic spedes. 

Selenenic acids and sym. diselenides from seleninic acids s. 13, 906 ... 

Furthermore, the authors demonstrated that excellent enantiomeric excesses can be obtained with hydrogen peroxide at -10°C by employing the sulfur-containing chiral diselenide 499 (Scheme 7.80). Se NMR indicated that the diselenide 499 suffered oxidation to seleninic acid or peracid. H NMR and NMR signals of the aliphatic moiety suggested that the sulfur has been oxidized too, thus the corresponding sulfone may be involved. 

Sym. diselenides from seleninic acids 2 R SeOgH RSeSeR... 

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