Selenide Reaction

There are similar procedures involving organic selenides. Reaction of ketones and aldehydes with phenylselenyl chloride occurs readily to give the a-seleno derivative, presumably by a mechanism similar to a-halogenation. Alternatively, ketones and esters can be converted to the a-seleno derivatives by reaction of the enolates with phenylselenyl chloride. The a-seleno compounds serve as precursors to a,jS-unsaturated carbonyl compounds because oxidation with hydrogen peroxide leads to spontaneous elimination of PhSeOH. 

Another possibility is that the selenide form of selenium may react with metals to form insoluble metal selenides (reaction 3), thus reducing their toxicity. Consistent with this possibility, Groh et al. (1973), using the scanning transmission electron microscope, found that the addition of mercury and selenium to diets for rats results in the formation of dense aggregates of black particles, composed of mercury and selenium, in the cells of the liver and kidneys. The molar ratio of selenium to mercury (Ganther and Sunde, 1974 Koeman et ai, 1975 Kosta et al., 1975) or cadmium (Gasiewicz and Smith, 1976) in the tissues is also consistent with this possibility. 

Naganuma et al., 1980). Selenide has been found to react with methyl-mercury in vitro to form bis(methylmercuric)selenide (reaction 10), but either protein sulfhydryl groups or reduced glutathione was needed when other chemical forms of selenium were used (Iwata et al., 1981). The detection of selenide, although at very low levels, in the tissues of mice treated with selenium and methylmercury (Naganuma et al., 1980) is evidence that this reaction occurs in animals. Hence, there are several possible mechanisms of interaction of selenium with cadmium, mercury, and silver, and many physiological aspects of this interaction still to be elucidated. 

These two gases can readily be prepared by the action of acids on selenides and tellurides respectively, the reactions being analogous to that for the preparation of hydrogen sulphide. 

Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions. 

AUylic phenyl selenides are obtained by the reaction of allylic acetates with diphenyldiselenide and Sml2[233]. 

Thus a second method was envisaged, the reaction of a nitrile, hydrogen selenide, and an a-halogenated ketone in the presence of a condensation catalyst, which can be POCl, or POCI3 with a Lewis acid such as PCI3 or anhydrous ZnCl. The use of fresh AICI3 leads to the formation of tarry side-products. 

The first involves the reaction of aziridine with an aldehyde or a ketone and the treatment of the resulting carbinol with hydrogen selenide (Scheme 69) (Methode I). 

Selenium heterocycles receive far less mention in the literature than do such homologs as oxazole, thiazole, or imidazole. In fact, preparative methods of selenium heterocycles are much more limited than for the other series, mainly because of manipulatory difficulties arising from the toxicity of selenium (hydrogen selenide is even more toxic) that can produce severe damage to the skin, lungs, kidneys, and eyes. Another source of difficulty is the reactivity of the heterocycle itself, which can easily undergo fission, depending on the reaction medium and the nature of the substituents. 

Alkylthiocyanates and alkylselenocyanates are obtained by treatment of trialkylboranes with potassium thiocycanate (260) and sodium selenoisocyanate (261), in the presence of iron(III) compounds, respectively. Unsymmetrical trialkylboranes react preferentially at the more highly branched alkyl group. Alkenylphenyl selenides are obtained by the reaction of alkenylboronic acids with phenylselenyl bromide (262). 

Detector elements are prepared either by sublimation in the presence of a small partial pressure of O2 or by chemical deposition from alkaline solution containing a lead salt and thiourea or selenourea (63). Lead sulfide and lead selenide deposit from solutions as mirror-like coatings made up of cubic crystallites 0.2—1 p.m on a side. The reaction may nominally be represented by the following ... 

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 ... 

Selenides. Selenium forms compounds with most elements. Biaary compounds of selenium with 58 metals and 8 nonmetals, and alloys with three other elements have been described (55). Most of the selenides can be prepared by a direct reaction. This reaction varies from very vigorous with alkah metals to sluggish and requiring high temperature with hydrogen. 

One area of research is the replacement of sulfur with selenium to enhance the potency of organic compounds in pharmaceutical apphcations. This has seldom been successflil and often the toxicity is increased. There are some exceptions, eg, selenazofurin, phenylaminoethyl selenide, ebselen, and selenotifen (64). Selenazofurin is a cytotoxic compound having antitumor properties, phenyl aminoethyl selenide is used to reduce hypertension, ebselen inhibits a variety of inflammatory and tissue damaging reactions, and selenotifen is an antiallergic agent. 

Both antimony tribromide and antimony ttiiodide are prepared by reaction of the elements. Their chemistry is similar to that of SbCl in that they readily hydroly2e, form complex haUde ions, and form a wide variety of adducts with ethers, aldehydes, mercaptans, etc. They are soluble in carbon disulfide, acetone, and chloroform. There has been considerable interest in the compounds antimony bromide sulfide [14794-85-5] antimony iodide sulfide [13868-38-1] ISSb, and antimony iodide selenide [15513-79-8] with respect to their soHd-state properties, ferroelectricity, pyroelectricity, photoconduction, and dielectric polarization. 

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 comparatively ready accessibility of selenocarboxamides has encouraged the use of this procedure for the synthesis of selenazoles (1889LA(250)294). Reaction of the a-chloro-carbonyl compound (73) with the selenocarboxamide (74) provided a ready synthesis of a variety of substituted selenazoles (75). Useful variations of this general procedure are described in detail in Chapter 4.20, and particularly attractive is the reaction of hydrogen selenide with a mixture of a nitrile and the a-halogenoketone to afford the selenazole (48YZ191, 79S66). 

Thermolysis of the aziridine (446) in the presence of diphenylketene gave a mixture of the pyrrolidone (447 minor product) and the oxazolidine (448 major product). In this instance the preferential addition to the C=0 bond is explained in terms of steric effects (72CC199). Similar addition to diphenylacetaldehyde takes place with the same orientation and the oxazolidine (448a) was obtained. When the reaction of the aziridine with the aldehyde was carried out in the presence of hydrogen selenide a selenazolidine was obtained (72BSB295). 

Mixed aryl selenides have also proven to be excellent ree ents for group transfer reactions.Photolysis of selenides in an inert solvent such as benzene can initiate chain reactions. Substituted radicals can be generated in this manner, from a-selenoe-... 

Appropriately substituted selenides can undergo cyclization reactions via a group transfer process. 

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). 

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