Selenides diselenides

The base dissolves the amphoteric gallium oxide and the acidic arsenic oxides. The selenide-diselenide solution dissolves residual arsenic, when present, by the reaction... 

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]. 

Trifluoromethyl thiirane is formed by the action of tris(diethylamino)-phosphineon l-chloromethyl-2,2,2-trifluoroethyldisulfide [S2] (equation 73) Difluoromethyl phenyl selenide is prepared by treatment of lithium phenyl-selemde with chlorodifluoroniethane via a carbene mechanism [Si] (equation 44) Bis(2,2,2-trifluoroethyl)diselenide is formed in the reaction of 2,2,2-trifluoroethyl mesylate with lithium diselenide [84] (equation 74). 

According to Hofman-Bang carbon sulfide selenide, CSSe, catalyzes the iodine-azide reaction but is at the same time decomposed with the formation of selenium. Experiments, in both this laboratory and that of Hofman-Bang have shown that carbon diselenide reacts with sodium azide (in aqueous or aqueous-alcoholic solution) with immediate precipitation of red selenium even at — 20° C. //a selena-triazole is formed in this reaction it must be extremely unstable. 

Kwon and coworkers have reported the use of diphenyl diselenide 2865"66 and a variety ofben/.ylic selenides (e.g. 29,67 615 30,69 3170 71 and 32K) as photoiniferters for polymerization of S, MM A and some derivatives. Very narrow dispersities were not obtained ( / Mn typically 2-2.5). However, it was possible to prepare... 

Diphenyl diselenide has been prepared by disproportionation of phenyl selenocyanate in the presence of potassium hydroxide" or ammonia/ and by air oxidation of benzeneselenol. The preparation of benzeneselenol is described in an earlier volume in this series/ In the present procedure phenylselenomagnesium bromide formed from phenylmagnesium bromide and selenium is oxidized directly to diphenyl diselenide with bromine/ Thus the liberation of the malodorous and toxic hydrogen selenide and benzeneselenol is avoided. Benzeneselenenyl chloride has been prepared by thermal elimination of ethyl chloride from ethyl phenyl selenide di-chloride/ by thermal elimination of chlorine from phenylselenium trichloride," and by chlorinolysis of diphenyl diselenide with either sulfuryl chloride " or chlorine. " ... 

The residue in the still (or alkali-insoluble material in the ether layer if Note 6 has been employed) contains diphenyl selenide (b.p. 167°/16 mm.) and diphenyl diselenide (m.p. 63°). It can be separated by a combination of distillation and crystallization from alcohol, but the amounts are small, and, unless the residues from several runs are combined, the procedure is not economical. 

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... 

When colloidal selenium was heated with mercuric trifluoroacetate or silver trifluoroacetate, bis(trifluoromethyl)diselenide was formed (43). Later work with selenium/silver carboxylate, RC02Ag (R = CF3, C2F5, or C3F7), mixtures at 280° C in a vacuum produced a mixture of the bis(perfluoroalkyl)selenide and the bis(perfluoroalkyl)diselenide (44). Formation of a polyselenium trifluoroacetate, which decarboxylates to produce the trifluoromethylselenides, was the proposed mechanism for R = CF3 (44). However, silver trifluoroacetate is a source of trifluoromethyl radicals when heated above 260° C (21), hence the trifluoromethylselenides may be formed by reaction of trifluoromethyl radicals with selenium, as in the reaction of CF3I with selenium [Eq. (34)] (45). 

Parkinson, B.A., Heller, A., and Miller, B., Effects of cations on the performance of the photoanode in the n-gallium arsenide/potassium selenide (K2Se)-potassium diselenide (K2Se2)-potassium hydroxide/carbon semiconductor liquid junction solar cell, /. Electrochem. Soc., 126,954,1979. 

An isocyanate intermediate may also be involved in the selenium-catalyzed process, which starts with the formation of carbonyl selenide from the reaction between selenium and CO, followed by nucleophilic attack by NuH (Scheme 28). When NuH = primary amine, the resulting RNH(CO)SeH intermediate may eliminate H2Se to give the isocyanate, which then reacts with Nu H to give the final product (Scheme 28, path a). Alternatively, oxidation of Nu(CO)SeH by 02 may lead to a bis(carbamoyl)diselenide species, which is attacked by NuH (Scheme 28, path b). 

Phenyl hydrogen selenide, generated from diphenyl diselenide and sodium borohydride in ethanol, promotes the /V-bcnzylation of cyclohex-2-enylamine (equation 54)164. 

The absence of dimer radical cation formation by diphenyl selenide under the pulse radiolysis conditions is in contrast to bimolecular reactions believed to occur under electrochemical conditions/ In these experiments, a rotating disk electrode was used in combination with commutative voltammetry under anhydrous conditions. The results led to the conclusion that reversible one-electron oxidation is followed by disproportionation, then reaction of the resulting dication with diphenyl selenide or an external nucleophile, with the likely intermediacy of the dimer dication (Fig. 33). As expected, the dihydroxy selenane is formed when water is present. Based on the kinetics of the electrochemical reaction, the authors believe the diselenide dication, not the radical cation, to be the intermediate that reacts with the nucleophile. 

Aryl trimethylsilylmethyl selenides also yielded the diaryl diselenide as the major product, but possibly through a somewhat different mechanism, due to the increased stability of the initially formed radical cation (Fig. 31) ... 

Table 15 Oxidation potentials and peak potentials of selenides and diselenides...

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. 

A number of companies are currently involved in thin-fllm photovoltaics [17], and low-cost multilayer thin-fllm amorphous silicon and CdTe (cadmium telluride) systems have already been installed in large numbers with efficiencies of the order of 10% and of about 80% output after 25 years of operation. Large-scale plants have been announced for the so-called CIS (cadmium indium selenide) and CGIS (copper gallium indium diselenide), technologies with production efficiencies in the range 12-13% and laboratory measurements up to 19.9% [18]. 

In the reaction between trifluoromethyl iodide and selenium at 265—290° bistrifluoromethyl selenide, (CF3)2Se, and bistrifluoromethyl diselenide, (CF3)2Sea, are produced in yields of 40 and 20% respectively (Table 4). These two compounds show a number of interesting reactions. The compound (CF3)2Se is converted quantitatively to CF3CI and, SeCl4 when irradiated in a quartz vessel with ultraviolet light. If the irradiation is done in Pyrex, however, a new solid compound CFjSeClg is formed, which hydrolyses to the crystalline acid CF3SeO(OH) (m.p. 118°). The... 

For the synthesis of selenocysteine derivatives that are suitable for peptide synthesis essentially two approaches have been used to date (1) conversion of p-chloroalanine 23 or serine-O-tosylate derivatives 24 into the desired selenocysteine derivatives by a nucleophilic displacement reaction with an areneselenol and (2) full reduction of selenocystine and in situ reaction with aryl halides to produce the aryl selenides. 7 25 In this context, reduction of selenocystine in 2 M NaOH with 2-methyl-2-propanethiol for concomitant formation of the mixed selenide/sulfide derivative 5e-(tert-butylsulfanyl)selenocysteine in analogy to the formation of 5-(fett-butylsulfanyl)cysteine 26 fails as a consequence of the difficult reduction of the diselenide with monothiols. 27 ... 

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