Dimethyl diselenide

Selenate is the most mobile form of Se. Selenium becomes biologically unavailable by reduction to elemental Se or by formation of metal selenides or Se-sulfides. Inorganic Se compounds can be converted to volatile organic Se such as dimethyl selenide or dimethyl diselenide by... 

R. rubrum was shown to possess hydrogenase and its activity was followed for 72 h. The bacteria were grown synchronously under anoxic conditions, with N2 or CO2 gas, at 30°C and in absence or presence of SeO . The production of dimethyl selenide and dimethyl diselenide was detected by chemiluminescence detection of samples of the gas phase (Fig. 9.12). After a 24 h exposure to complete darkness, the bacteria were transferred to the experimental conditions and changes in the activity of hydrogenase with time were studied in non-growing cells, cultivated in white light. 

Dimethyl selenide, (CH3)2Se.—An intimate mixture of selenium and amorphous phosphorus (5 2) is heated, and the black mass powdered and heated in a retort with concentrated sodium hydroxide and potassium methyl sulphate. The mixture foams and a yellow liquid distils over. This is separated from the water and fractionated to remove dimethyl diselenide, which is present in small quantity. 

Scrambling equilibria in mixtures of dimethyl selenide and dichloro-diselenide as well as dimethyl diselenide and dichloro diselenide have been investigated recently (103). The reactions observed at room temperature to occur in such mixtures are scrambling of methyl groups and chlorine atoms on selenium as well as condensation polymerization resulting from the elimination of methyl chloride. 

In the interaction of dimethyl diselenide and dichloro diselenide, it was shown by proton NMR that the first more-condensed species than the diselenide to appear in the spectra is the mixed tetraselenide, CH3SeSeSeSeCl, Eq. (161). 

The most common methods for the preparation of 1-benzoselenophene and its analogs involve the annulation of the selenophene ring onto a benzene substrate. Early works, such as reaction of selenium with phenylacetylene or the reaction of selenium dioxide with styrene, gave low yields but more recently elaborated procedures, e.g., gas-phase reaction of cinnamaldehyde with dimethyl diselenide at 630 °C, give 1-benzoselenophene in high yield [131, 132],... 

The lithiation of 1,3-oxathiane (296) takes place with s-BuLi at —78 °C to give 2-lithio-1,3-oxathiane (315), an analogue of 2-lithio-l,3-dithiane (161), but with lower stability487. This intermediate reacts with different electrophiles, such as alkyl halides, carbonyl compounds, benzonitrile, dimethyl disulfide, dimethyl diselenide, trimethylplumbyl acetate and trimethylsilyl, germyl and stannyl chlorides488,489. However, further deprotection of 2-substituted 1,3-oxathianes has not been reported yet. 

The gas-phase thermal reaction of cinnamaldehyde with dimethyl diselenide at 630 °C gave benzo[ ]selenophene 2 <1998RCB447>. 

The tin(IV) chloride mediated addition of dimethyl diselenide to disubstituted alkenes proceeds rapidly at room temperature and affords in good yield the corresponding 1,2-bis(selenides) as single stereoisomers107. 

Reaction of diphenyl diselenide or dimethyl diselenide with hydrazine hydrate and sodium hydroxide generates the corresponding selenolates smoothly in solvents like DMF or diethyl ether and in the presence of tetrabutylammonium chloride as a phase-transfer catalyst [13]. The selenolates react with organic halides to give various selenides (Scheme 9). Similar conditions have been applied to the synthesis of aryl vinyl selenides from diaryl diselenides and acetylene [14]. 

Selenolates prepared from diphenyl or dimethyl diselenide by reduction with NaBH4 smoothly transform various benzylic alcohols 24 into the corresponding selenides 25 in the presence of aluminum chloride (Scheme 30 a) [41]. AICI3 is considered to activate the alcohol substrate by coordinating to the oxygen. Similar transformations are possible by the reaction of alcohols with phenyl selenocyanate in the presence of tributyl phosphine [52]. When the selenolate is reacted with aromatic aldehydes or ketones 26 in the presence of AICI3, the corresponding benzylic selenides 27 are obtained in moderate yields (Scheme 30b) [41]. 

Tetrabromocyclopropene (21) reacted very readily with dimethyl diselenide and with dimethyl ditelluride to give the tris(methylchalcogeno)cyclopropenylium tribromidcs 22 in high yield. The reaction with dimethyl disulfide was slower but also afforded the tris(methylsulfanyl)cyclo-propenylium salt in high yield. 

Conditions such as pH, oxidation-reduction potential, and the presence of metal oxides affect the partitioning of the various compounds of selenium in the environment. In general, elemental selenium is stable in soils and is found at low levels in water because of its ability to coprecipitate with sediments. The soluble selenates are readily taken up by plants and converted to organic compounds such as selenomethionine, selenocysteine, dimethyl selenide, and dimethyl diselenide. Selenium is bioaccumulated by aquatic organisms. Very low levels of selenium are found in ambient air. 

The selenium compounds that are most likely to be encountered in air in occupational settings are dusts of elemental selenium, hydrogen selenide, and selenium dioxide. Other volatile selenium compounds (e.g., dimethyl selenide, dimethyl diselenide) might be encountered in some naturally occurring situations. Because selenium is converted from one form to another, as in plant biosynthesis of selenoamino acids, it is not clear which specific forms may be encountered at hazardous waste sites. If a hazardous waste site specifically contains deposits of compounds of selenium, those compounds could be released off-site in dust or air. Toxicity data for exposures via inhalation are available for elemental selenium, selenium dioxide, selenium oxychloride, hydrogen selenide, and dimethyl selenide. Because there are few studies of inhalation of selenium of any single form, all available studies of inhalation exposures to selenium compounds will be included in this discussion. 

The amount of selenium contributed to the air by other sources is not known. Microbial action within the soil may also contribute selenium to the air (Fishbein 1983). Selenium biomethylation volatilizes about 3,000 tons of selenium per year into the atmosphere, which eventually returns to earth in rainfall (NAS 1976a). Volcanic gas is suspected to be the major natural source of atmospheric selenium. Certain plants metabolize inorganic selenium compounds to volatile selenium in the forms of dimethyl selenide (Lewis et al. 1971) and dimethyl diselenide (Evans et al. 1968). Animals are also capable of volatilizing selenium and releasing dimethyl selenide in expired air (Schultz and Lewis 1940). 

The volatile selenium compounds that partition into the atmosphere include the inorganic compounds selenium dioxide and hydrogen selenide and the organic compounds dimethyl selenide and dimethyl diselenide. Hydrogen selenide is highly reactive in air and is rapidly oxidized to elemental selenium and water (NAS 1976a), but the other compounds can persist in air. 

Evans CS, Asher CJ, Johnson CM. 1968. Isolation of dimethyl diselenide and other volatile selenium compounds from Astragalus racemosus (Pursh.). Aust J Biol Sci 21 13-20. 

Preparation. The reagent is prepared in nearly quantitative yield by reduction of dimethyl diselenide with sodium in liquid ammonia. 

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