Diselenoic acids

For the preparation of secondary and tertiary selenoamides, several methods have been used reaction of lithium alkyneselenolates (obtained using metallic selenium) with amines, aromatic diselenoic acid Se-methyl esters with amines or dihalomethane with elemental selenium, NaH and amines (Scheme 83).258 266... 

The acids thus produced are crystalline products, which are not very stable and show a tendency to pass into diseleno-acids. Some are fairly stable in neutral solution, but yield diseleno-acids in the presence of alkalis, whereas others yield the latter class of acids on prolonged treatment with dilute mineral acids. 

Keywords Selenothioic acid Diselenoic acid Se-substituted selenothioate Se-substituted selenothioate Diselenoate... 

Selenothioic and diselenoic acids and their derivatives were once a rare class of compounds indeed, a review of them [1] pubhshed in 1995 summarized their chemistry in just a few pages. Since then, however, their chemistry has developed rapidly, and several types of derivatives have been prepared by appropriate methods. Syntheses of these compounds were exhaustively described in the review [2] pubhshed in 1998. In this article, selenothioic and diselenoic acids and their derivatives are reviewed in terms of theoretical techniques, syntheses, and reactions. 

A few metal complexes of selenothioic and diselenoic acids have been reported. In a study on the reactivity of metal-carbon triple bond compounds toward chalcogens, it was found that molybdenum (52) and tungsten (53) carbyne complexes reacted with elemental selenium to yield the corresponding di-selenoate complexes 54 and 55, respectively (Eqs. 13 and 14) [18]. 

Selenothioic acid Sc-esters serve as thioacylating agents toward amines and alcohols. Similarly, selenothioic acid S-esters and diselenoic acid esters can be used as selenoacylation agents. In addition, their thiocarbonyl and selenocar-bonyl groups act as dienophiles. The reactions of S-substituted selenothioates with electrophiles under basic conditions were investigated in detail. 

Although ammonium salts and inner salts of selenothioic and diselenoic acids have been synthesized, isolation of their free acids has yet to be achieved. Eight selenothioates I-VIII and four diselenoates IX-XII are possible if we take all of... 

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