Dimethyl selenide

The natural abundance of selenium-77 is 7.58%. The chemical shift of dimethyl selenide is set equal to 0 ppm. The total chemical shift range is around 2200 ppm, organoselenium compounds covering almost the whole range. Figure 41 shows the spectrum of H2Se03 in D20, the linewidth being only... 

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. 

Plant-mediated volatilization of inorgaiuc compounds is an accepted method for reclaiming selenium-contaminated lands. Volatile Se is formed mostly from dimethyl selenide, evolving from the land surface. For example, dimethyl selenide... 

Musaev and Hirao have also reported theoretical studies on the reaction mechanisms of dimethyl sulfide and dimethyl selenide with peroxynitrite (ONO—0 )" ° . 

Several cyclobutenes can be synthesized by elimination of selenoxides from the corresponding methyl- or phenylselanyl derivatives 58 or by elimination of dimethyl selenide from the corresponding selenonium salts 60. The results of these conversions are summarized in Table l.23 The cyclobutenes have been used as precursors for substituted butadienes.23... 

The analogous cations 29 and 30 readily formed in HZSM-5, HY, and even the much weaker acid HX by the reaction of methanol with dimethyl sulfide or dimethyl selenide (145). Formation of the trimethylselenonium ion in zeolite HZSM-5 was established unambiguously by the observation the 77Se resonance (22 ppm downfield of dimethyl selenide). Extensive evaluation of the reactivity of methanol in the presence of trimethylchalco-genonium ions found no evidence of a rate enhancement in MTG chemistry, and this mechanism (Scheme 2) was rejected. 

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. 

Dimethyl selenium dinitrate, (CH3)2Se(N03)2.-—Dimethyl selenide in small quantities is dissolved in concentrated nitric acid. Long, prismatic crystals separate, which correspond to the hydroxynitrate,... 

Diphenyl selenide is a colourless, strongly refractive oil, B.pt. 167° C. at 16-5 mm. insoluble in water but miscible with alcohol or ether in all proportions. It has a faint odour, and a density of 1 3712 at 0° C., 1 3561 at 15 2° C., and 1 350 at 20° C. With cold bromine in ether solution it yields the dibromide. Diphenyl selenide, unlike dimethyl selenide, does not combine with alkyl iodides, and in this respect it resembles diphenyl sulphide.2 When heated nearly to its boiling-point with sulphur it gives diphenyl sulphide, the reaction being practically quantitative at 300° C.3 With palladium chloride it forms the complex PdCl2.2(C6H5)2Se, orange-red needles, M.pt. 181° to 182° C.4... 

Dimethyl selenide, 28 grams, is added to 43 grams of benzyl bromide, the resulting brown mass dissolved in water, and the picrate precipitated by the aid of sodium picrate. The yield is about 38 grams, the product separating from alcohol in small needles, M.pt. 118° C. 

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. 

Organic selenides, e.g. dimethyl selenide (Me2Se), are especially important in aquatic systems. 

Tanzer, D. and K.G. Heumann. 1990. GC determination of dimethyl selenide and trimethyl selenonium ions in aquatic systems using element specific detection. Atmos. Environ. 24 3099-3102. 

It is well known that the toxicity of many elements depends on the physicochemical forms they assume. So, for instance, determining the total content of a certain element in a sample is definitely not sufficient to measure its toxicity. Selenium is a case in point in small amounts this element is essential to human health. But the transition from the necessary amount (about 70pg of selenium per day for an adult) to a toxic dose (about 800 pg of selenium per day) is relatively easy. In rats, moreover, the fatal dose of Se(IV) compounds is 3.2 mg kg 1 of body mass, whereas for dimethyl selenide it is 1600 mg kg 1 of body mass. Nonorganic selenium compounds [Se(IV) and Se(VI)] are believed to be the most toxic ones, whereas in the environment selenium occurs most commonly bound to amino acids (selenomethionine and selenocysteine). The least toxic forms seem to be the volatile methyl compounds of selenium, which are metabolites of a detoxication process. 

Sodium selenite and selenodiglutathione have been found to be more effective in inhibiting the growth of Ehrlich ascites tumors than sodium selenide, dimethyl selenide or seleno-DL-cystine. Preincubation of tumor cells with either 1 or 3 ppm Se as GSSeSG, Na SeO or dimethylselenide before reinoculated into mice resulted in a significant increase in survival in mice inoculated with cells pretreated with GSSeSG (69) (Table IV). Vernie et al.,... 

Adapted from Poirier and Milner (69). All tumor cells were preincubated for 15 minutes in buffer in the presence or absence of selenium as sodium selenite, selenodiglutathione or dimethyl-selenide, before inoculation into Swiss mice. Each received 5 X 10 Ehrlich ascites tumor cells. Vertical means SEM not sharing a common superscript letter differ P < 0.05. 

TEA (Transverse Electrical discharge in gas at Atmospheric pressure) CO2 laser irradiation into gaseous mixtures of 1,3-disilacyclobutane and dimethyl selenide results in chemical vapor deposition of novel polyselenocarbosilane films <2006MI178>. 

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