Seleninic acid anhydrides

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... 

There has been recent controversy over the reduction of seleninic acids (RSe02H) to selenenic acids (RSeOH). Reich et al and Kice et a/. have independently concluded that earlier claims for the isolation of stable selenenic acids are probably in error. While selenenic acids are stable in dilute solution, they show a pronounced tendency to form the corresponding anhydrides in the absence of water. 

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]. 

Since seleninic acids and their anhydrides are much more stable than the corresponding selenenic compounds, they can be employed as starting materials for the synthesis of selenenic acids and their anhydrides. Reduction of seleninic acids and their anhydrides with appropriate reducing reagents such as hydrazines [35], hypophosphorous acid (H3PO2) [36], and thiols [37] is a useful alternative method for the synfhesis of selenenic acids and their anhydrides. 

Seleninic acids and their anhydrides, RSe(O)OH and RSe(O)OSe(O)R, are used as versatile and specific oxidizing reagents for a variety of organic compounds. In contrast with selenenic acids, seleninic acids (and their anhydrides) are stable, especially, benzeneseleninic acid, PhSe(O)OH, and benzeneseleninic anhydride, PhSe(O)OSe(O)Ph, which are commercially available. 

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]. 

Finally, aromatic sulphonic acids have been readily formed by the reaction of the corresponding sulphinic acid with benzeneseleninic acid (the selenium equivalent of a sulphinic acid) in a range of solvents, at low temperatures (equation 59)295. A selenosul-phonate is also formed. Benzeneseleninic anhydride [PhSe (0)0Se(0)Ph] may be used in the reaction in place of the seleninic acid. 

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. ... 

Important uses of selenenic and seleninic acids and anhydrides (see also the later sections) have been established, in the synthesis of )ff-silyloxy-a-(phenyl-seleno)aldehydes from allyl silyl ethers (Scheme 3) and in the high-yield syntheses of 2-acetoxyalkyl phenyl selenides [using PhSe(0)OH and AcOH j and... 

Seleninic acids are effective catalysts for the conversion of alkenes into oxirans and of sulphides into sulphones by H2O2. They can be used for the partial oxidation of thiols, three equivalents of the thiol with PhSe(0)0H giving equimolar amounts of PhSeSR and RSSR. Benzeneseleninic anhydride (ref. h), formed by oxidation of PhSeSePh with or with t-butyl hydroperoxide, ... 

Valerolactones.— The unstable dihydropyran anion (73) may be useful for the preparation of a-substituted valerolactones the intermediate dihydropyrans are converted into the latter by acid hydrolysis and Collins oxidation. A new route to the c/s-fused valerolactone portion of vemolepin has been developed which could have other applications. It has been briefly noted that benzene-seleninic anhydride can be used to dehydrogenate fused valerolactones to the a,j8-unsaturated derivatives the conditions, however, are somewhat drastic (120 °C, 42 h). Unsaturated valerolactones can also be obtained from vinyl-oxirans by a light-induced reaction with pentacarbonyliron followed by carbonyl-ation. ... 

Ketosteroids are smoothly oxidized to the l,4-dien-3-ones by benzene seleninic anhydride. Barton and his group have now made this reaction catalytic in selenium by developing the use of iodylarenes for the in situ oxidation of diphenyldiselenide to the anhydride. m-Iodylbenzoic acid was chosen to aid the isolation of the product and the recovery of the aryl iodide. 

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