From Oxide Selenides

Under certain conditions, the action of H2Se on M2O3 gives oxide selenides as intermediate reaction products. These can be converted in a second reaction step into the 0-free M2Se3 or M3Se4 (see pp. 33 and 30), Obolonchik et al. [20, 21 ], also see Skripka [23], Skripka, Obolonchik [24]. 

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With bromine, diorganosulfldes tend to furnish charge transfer adducts, whereas selenides can give equilibria between C.T. adducts and products from oxidative addition, i.e. molecular Se(IV) compounds.23 A particular example of such equilibria is the bromination of selenanthrene reported by Nakanishi et al.24 (see Chapters 8.2 and 10.3).24... 

To some extent the vitamin E requirement may be lessened by the presence in the diet of synthetic antioxidants and by selenium. Much evidence supports a relationship between the nutritional need for selenium and that for vitamin E. Lack of either causes muscular dystrophy in many animals as well as severe edema (exudative diathesis) in chicks. Since vitamin E-deficient rats have a low selenide (Se2 ) content, it has been suggested that vitamin E protects reduced selenium from oxidation.) Vitamin C (ascorbic acid), in turn, protects vitamin E. 

The substitution product was obtained in modest yield when the reaction was performed with PhSe ions153. On the other hand Na2Se, formed in liquid ammonia from Se and Na metals, reacted with neopentyl iodide (97) to give dineopentyl diselenide (100) from oxidation of 98 (equation 73b), together with a small amount of dineopentyl selenide (99) (equation 73 a)155. 

Selenoxides derived from unsymmetrical selenides are chiral and stable toward pyramidal inversion at room or even higher temperatures. They are produced enantioselectively by the use of chiral oxidants such as the Sharpless reagent or camphor-derived oxaziridines or diastereoselectively with achiral oxidants when one of the selenide substituents is itself chiral (see Section 9). Racemic selenoxides have been resolved by chromatography over chiral adsorbents. Chiral selenoxides racemize readily in water, particularly under acid-catalyzed conditions, presumably via the intermediacy of achiral selenoxide hydrates (equation 2). 

The data of Table 6 ), determined by internal cahbration on polycrystalline materials show the expected increase in covalency from oxide to sulphide ( 2x) and from sulphide to telluride. The sulphide, selenide and diselenide are all seen... 

The transformation of carbonyl compounds to a,p-unsaturated carbonyl compounds can be achieved by selenoxide elimination. In fact, this method is superior to the sulfoxide elimination, because of the milder conditions employed and the direct formation of the unsaturated product, without isolation of the selenoxide. Thus, oxidation of the seleitide 25 at 0 °C gave the a-methylene lactone 26, a structural unit found in cytotoxic sesquiterpenes (2.27). The requirement for a syn elimination pathway forces the reaction to proceed to give only the product 26 and none of the regioisomeric a,3-unsaturated lactone 28. However, the lactone 28 is the major product from oxidation of the selenide 27, illustrating the importance of the stereochemistry of the selenide, derived from the order of addition of the phenylselenyl and methyl groups, in determining the regiochemical outcome. 

Sulfides can be oxidized to sulfoxides by reaction with NCS in methanol (0°C, 1 h). Similarly, selenides couple with amines when activated by NCS to form selenimide species. These have been generated from allylic selenides in order to prepare allylic amines and chiral secondary allylic carbamates by [2,3]-sigmatropic rearrangement (eq 8). ... 

From the oxide From the sulphide From the selenide... 

Trioctylphosphine oxide (TOPO) caps are used in quantum dots for LEDs moreover, the CdSe cores of these quantum dots can be obtained directly from cadmium selenide complexes as (12.401) [18,19]. Both TOPO and TOP can be used to produce various nanocrystals [20,21], Quantum dots of InP and GeP are being explored [22,23], Nickel nanoparticles, stabilised by TOPO, have been converted to Ni2P nanoparticles by the action of white phosphorus [21]. Highly luminescent nanocrystals of InP have been obtained. 

As exemplified in the following cases, this addition reaction has often been used as the first step in the preparation of vinyl sulfones. The adduct must therefore undergo a subsequent elimination reaction. A base is needed to perform dehydrohalogenation. The selenides resulting from the addition of selenosul-fonates can be eliminated very smoothly through oxidation. Thus, Yus and co-workers [104] have based a very simple method for the preparation of j9-sulfonyl-a,j9-unsaturated compounds on the addition of tosyl iodide to Michael acceptors (equation (50)) whereas Barton et al. [105] have shown that the addition of phenylseienotosylate to electron-rich olefins, catalyzed by Ru(II) complexes, is efficient (equation (51)). An alternative approach is the Ce(IV)-mediated addition of arylsulfinates to electron-rich olefins which proceeded directly to the olefinic product resulting from oxidative elimination of the intermediate alkyl radical (equation (52)) [106]. 

YSe, like Y3Se4 and Y2Se3, is stable in dry air at room temperature. However, the slightest trace of water caused the surface of the selenide to turn black and, eventually, the entire sample would disintegrate. Selenium vapor evolves on heating in vacuum, probably around 650°C. Oxide selenides or selenates form superficially from YSei le temperatures above 400°C in poor vacuum, Norman [1]. 

Sulfation Roasting. Acid roasting technology (Fig. 2) rehes on differences in the volatiUty of the tetravalent oxides of selenium and tellurium at roasting temperatures of 500—600°C to selectively volatilise selenium from slimes. Acid roasting uses sulfuric acid as the oxidant for the conversion of selenium/selenides and tellurium/teUurides to their respective tetravalent oxides. Typical oxidation reactions are as foUow ... 

Wet chlorination is performed by sparging slimes slurried either in water or hydrochloric acid using chlorine gas, or other oxidants such as sodium chlorate or hydrogen peroxide which Hberate chlorine from hydrochloric acid, at about 100°C. Under these conditions, selenium and selenides rapidly oxidize and dissolve. 

Trialkyl- and triarylarsine sulfides have been prepared by several different methods. The reaction of sulfur with a tertiary arsine, with or without a solvent, gives the sulfides in almost quantitative yields. Another method involves the reaction of hydrogen sulfide with a tertiary arsine oxide, hydroxyhahde, or dihaloarsorane. X-ray diffraction studies of triphenylarsine sulfide [3937-40-4], C gH AsS, show the arsenic to be tetrahedral the arsenic—sulfur bond is a tme double bond (137). Triphenylarsine sulfide and trimethylarsine sulfide [38859-90-4], C H AsS, form a number of coordination compounds with salts of transition elements (138,139). Both trialkyl- and triarylarsine selenides have been reported. The trialkyl compounds have been prepared by refluxing trialkylarsines with selenium powder (140). The preparation of triphenylarsine selenide [65374-39-2], C gH AsSe, from dichlorotriphenylarsorane and hydrogen selenide has been reported (141), but other workers could not dupHcate this work (140). 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

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