Selenium compounds reductions

In many reactions, selenium is an oxidant as well as a reductant. Strong oxidants convert selenium dioxide and its derivatives to the hexavalent state. Although hexavalent selenium compounds are oxidants, these are less active and difficult to reduce. Selenium salts resemble the corresponding sulfur and tellurium salts in behavior. 

The reaction of selenium with CO and H2O in fhe presence of tertiary amines generates amine salts of hydrogen selenides ([HSe ]- [R3NH], =1 or 2), which can be used for the synthesis of selenium compounds such as selenides, diselenides, and selenocarbonyl compounds and for fhe selective reduction of carbonyl, nitro, and olefinic compounds [118]. 

Other reductions using selenium compounds involve the stereospecific deoxygenation of epoxides by use of selenocyanates or selenoamides [178]. 

There is no evidence to support a causal association between selenium compounds and cancer in humans. In fact, some epidemiological and experimental evidence suggests that selenium exposure under certain conditions may contribute to a reduction in cancer risk. Currently, the chemopreventive potential of selenium is under research. Selenium sulfide and ethyl selenac are the only selenium compounds that have been shown to be carcinogenic upon oral administration in rodents however, significant exposure to these forms of selenium is extremely unlikely. 

A study completed by Bender et al. (1991) using a simulated laboratory pond found that bacteria and cyanobacteria have two possible mechanisms for the uptake and transformation of selenate. The uptake mechanism involves the reduction of selenate to elemental selenium that will be physically held within the biological mat. The microorganisms were also found to cause the transformation of soluble selenium into volatile alkyl selenium compounds (Bender et al. 1991). 

Inorganic selenium compounds are metabolized by reduction to selenide, followed by methylation or enzymatic conversion to selenophosphate, which serves as the reactive form of selenium for the synthesis of selenocysteine-containing selenoproteins. Whereas selenite requires no specific activa-... 

There are many papers which contain large-ring selenium compounds that involve functional group transformations which do not involve the selenium atom. One example being the many reactions of (28), for example reduction to the alcohol, elimination to the alkene, Grignard reactions, etc., which produce derivatives which have been used in neurotropic and psychotropic studies <69CCC3801>. 

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