Selenium bromide

Selenathietanes also were first prepared by a Soviet research group in 1978. By treating diethylene sulfone with selenium bromide (Eq. 79) the brominated selenathietanone 292 was formed it could be further brominated to 293. 

Selenium bromide, Se2Br2, decomposes in contact with water according to the equation... 

The method of estimation of selenium in sulphur depends upon the fact that sulphur and selenium bromides are decomposed by water according to the equations ... 

The Grignard reagent may be used as in method (2) for aiyl selenides, and the selenium may be replaced by selenium bromide. 

The diselenides occur as by-products when aryl magnesium bromides react with selenium bromide in ether. 

In very poor yield when benzene reacts with selenium bromide in carbon disulphide solution in the presence of aluminium chloride. 

Benzene (3 parts) and one part of selenium tetrachloride are heated together under reflux in the presence of anhydrous aluminium chloride until no further evolution of hydrogen chloride occurs.3 Benzene, aluminium bromide and selenium bromide interact to give bromobenzene and a 22 to 27 per cent, yield of diphenyl selenide.4... 

Phenyl magnesium bromide and selenium bromide react to form diphenyl selenide as one product.5... 

Di-m-aminophenyl selenide, (C6H4NH2)2Se,5 obtained from magnesium m-aminophenyl bromide and selenium bromide, is a yellowish-brown, heavy, viscous oil, B.pt. 130° to 150° C. in vacuo. When treated with an ether solution of bromine it yields the compound (Br.C6H3.NH2.HBr)2Se, which crystallises in tufts of needles, M.pt. 115° to 116° C. 

Five per cent, of selenium in excess of that required by the foregoing equation is used. The mixture is heated for twelve hours at 220° C., then for a short time at 235° to 240° C. By this method the selenide is obtained in rectangular plates, M.pt. 61° to 62° C., B.pt. 186° C. at 16 mm. When aluminium and selenium bromides react with toluene, the chief product is o-bromotoluene, but a small amount of di-o-tolyl selenide also results, B.pt. 174° to 180° C. at 13 mm.8 It yields a dibromide on treatment with bromine and a nitrate with nitric acid. 

Diphenyl diselenide, (CeH5)2Se2, is formed as a by-product in the preparation of phenyl selenide when magnesium phenyl bromide in ether solution reacts with selenium.5 A 2 per cent, yield is obtained when benzene, aluminium and selenium bromides react in dilute carbon disulphide solution. The product melts at 62° C.6 The corresponding oxide is an oil, B.pt. 230° C. at 65 mm.,7 and the sulphide, (C6H5)2Se2S, M.pt. 55° C., is obtained from sulphur chloride and phenyl selenide in carbon disulphide solution.8... 

These derivatives fall into two classes, the first containing an unsubstituted nucleus, and the second having alkoxy-groups in the nucleus. The former may be represented by triphenyl selenium chloride, prepared by adding diphenyl selenium dichloride to a suspension of aluminium chloride in dry benzene. This chloride is crystalline, absorbs atmospheric moisture to yield a dihydrate, and decomposes at its melting-point, forming diphenyl selenide and chlorobenzene. Boiling with ethylene dibromide converts it into triphenyl selenium bromide. The hydroxide has not been isolated in the solid state, but salts have been prepared. The alkoxy-derivatives are represented by... 

Triphenyl selenium bromide, (C6H5)3SeBr, is formed when the foregoing chloride is dissolved in boiling ethylene dibromide. It is crystallised from methyl ethyl ketone and melts with decomposition at 236° C., heating at this temperature causing decomposition with formation of diphenyl selenide and bromobenzene. 

The Selenide [(NHCgHg.CO CSe. —This occurs when malon-anilide (5 mols.) and selenium tetrachloride (4 mols.) react in absolute ether at 27° to 30° C. The product darkens at 217° C. and melts at 222° to 223° C. Malon-m-chloroanilide also occurs during the preparation. Reduction of the selenide by alkali hydrosulphite affords the original anilide and hydrogen selenide, whilst treatment with bromine gives dibromomalonanilide and selenium bromide. 

With a polymer-bound chiral selenium bromide reagent, the stereoselective activation of olefins has been accomplished (entry 19) 24 Uehlin and Wirth24 found that both mesoporous silica and polystyrene-supported... 

Very recently, using polystyrene beads, the preparation of some polymer-sup-ported selenium reagents has been described by Nicolaou [28]. Polymer-bound selenium bromide and selenium phthahmide act as efficient selenenylating agents of alkenes. In view of their versatility and ease of handhng these reagents can find useful applications in sohd phase and combinatorial synthesis. 

With the aim of enhancing the stereoselectivity of this cyclization processes Lipshutz [25] used the (2,4,6-trisisopropylphenyl)selenium bromide derived from the diselenide 17. The results of these reactions are also collected in Scheme 17. Interesting results were obtained with the ( )-olefins 112 and 113,... 

Scheme 17. Stereoselectivity of the Cyclizations of Homoallylic Alcohols to Tetrahydrofurans Promoted by N-(Phenylseleno)phtalimide (A) and by (2,4,6-Trisisopropylphenyl)selenium Bromide (B)...

By further evaluation of the redox system SeBr4/SeBr2/Se/Br in aprotic solvents (Section III,A), the first examples of bromoselenates-(II,IV) containing selenium in both oxidation states +2 and +4 were prepared. Three dinuclear, trinuclear, and tetranuclear types of anions are reported in this novel class of mixed-valence compounds Se2Brg, SeaBrio , and Se4Bri2 . They are shown in Fig. 31. Similar to the bromoselenates(II), they were obtained by nucleophilic addition reactions of bromide ions within the complex reaction mixtures of selenium bromides. Evidently, the formation of Bra" is important for the stabilization of Se(II) in addition to Se(IV), shifting the equilibrium... 

Selenium is usually separated by distillation as the volatile selenium bromide (SeBr4) or chloride (SeCU) [1,2]. Selenium is distilled from concentrated HBr medium [in the presence of bromine to prevent the reduction of Se(IV)] and from concentrated HCl. Perchloric or sulphuric acid is added to the still, and distillation is continued until white fumes of H2SO4 or HCIO4 appear. Passage of nitrogen through the liquid promotes the distillation. During the distillation, Te remains quantitatively in the still, but As, Ge, and Sb are distilled with the selenium. 

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