Selenides Seleninic acids

Dibenzyl diselenide crystallises from alcohol in yellow needles, which are slightly deeper in colour than those of the p-nitrobenzyl compound, and melt at 92° to 93° C. Exposure to light for an hour or so causes the crystals to turn red. The selenide readily dissolves in hot alcohol, but is only sparingly soluble in ether, insoluble in water. Oxidation with fuming nitric acid converts it into benzyl seleninic acid, and boiling with copper or mercury in suspension precipitates selenium. Boiling with iodine in chloroform solution gives the tetra-iodide, M.pt. 98° C. the tetrabromide melts at 137° C.5... 

Methyl-j8-naphthylselenone, C10H7.SeO2.CH3, occurs when the sodium salt of naphthalene-j8-seleninic acid in methyl alcohol is boiled with methyl iodide for a long period. After treatment with water and extraction with ether, removal of the latter and crystallisation from alcohol gives a 48 per cent, yield as golden-yellow crystals, M.pt. 136° C. The selenone may also be obtained by the oxidation of methyl-j3-naphthyl selenide with permanganate. 

It has already been pointed out that this compound may be prepared by hydrolysis of the selenocyanate it may also be obtained by the interaction of sodium selenide and 1-chloroanthraquinone. By the latter process orange-red plates, M.pt. 212° C., result. If 2-chloroanthra-quinone be used in the reaction, 2-anihraquinone selenophenol is obtained as an orange-yellow product, which gives a violet-red solution in sulphuric acid. Concentrated nitric acid causes oxidation to the seleninic acid. 

SELENIDE, DIALLYL- see DBL300 SELENINIC ACID, PROPYL- see PNV760 P-SELENINOPROPIONIC ACID see SBN510 SELENINYL CHLORIDE see SBT500 SELENIOUS ACID see SBOOOO SELENIOUS ACID, DIPOTASSIUM SALT (9CI) see SBOlOO... 

One of the major drawbacks of these reactions is clearly the unavailability of the whole set of alkyl phenyl selenones due to side reactions which occur during their preparations. Methyl, n-alkyl and some cyclopropyl phenyl selenones are available from the corresponding selenides and potassium permanganate, peroxycarboxylic acids or hydrogen peroxide/seleninic acids mixtures, whereas s-alkyl phenyl selenones, 2,2,3,3-tetramediylcyclopropyl selenone and benzyl phenyl selenone are not available in these ways. 

Elimination of water is particularly favored from p-chlorophenyF and (p-trifluoromethyl)phenyl selenides, whereas elimination of seleninic acid is mainly observed from methylseleno derivatives. Here, two different effects work in the same direction. The arylseleno group, more than the methylseleno group, makes the a-hydrogen acidic, and has at the same time a lower tendency to stabilize a p-caib-enium ion via the formation of a seleniranium ion. 

A 30% solution of hydrogen peroxide in water was purchased from Mallinckrodt Chemical Works. The reaction requires 2 molar equivalents of hydrogen peroxide, the first to oxidize the selenide to the selenoxide and the second to oxidize the elimination product, benzeneselenenic acid, to benzene.seleninic acid. The submitters recommend that the hydrogen peroxide solution be taken from a recently opened bottle, or titrated to verify its concentration. 

Selenoxide elimination is now widely used for the synthesis of a,p-unsaturated carbonyl compounds, allyl alcohols and terminal alkenes since it proceeds under milder conditions than those required for sulfoxide or any of the other eliminations discussed in this chapter. The selenoxides are usually generated by oxidation of the parent selenide using hydrogen peroxide, sodium periodide, a peroxy acid or ozone, and are not usually isolated, the selenoxide fragmenting in situ. The other product of the elimination, the selenenic acid, needs to be removed from the reaction mixture as efficiently as possible. It can disproportionate with any remaining selenoxide to form the conesponding selenide and seleninic acid, or undergo electrophilic addition to the alkene to form a -hydroxy selenide, as shown in... 

Selenides s. Silyl-selenides, Stannyl-Seleninic acids... 

Important uses of selenenic and seleninic acids and anhydrides (see also the later sections) have been established, in the synthesis of )ff-silyloxy-a-(phenyl-seleno)aldehydes from allyl silyl ethers (Scheme 3) and in the high-yield syntheses of 2-acetoxyalkyl phenyl selenides [using PhSe(0)OH and AcOH j and... 

Similarities are noted between the mass spectra of aliphatic and aromatic selenides with analogous sulphides and phosphines. " Selenoxides show the expected fragments derived from the selenate rearrangement product " " Extensions of these studies cover selenium dihalides (no moleculm ion is seen " ), seleninic acids and esters, " and selenones. Mass spectra of diaryl tellurides are very much like those of S and Se analogues. ... 

Quaternization of selenides with methanesulphonyl fluoride or methyl iodide-silver tetrafluoroborate, followed by elimination with potassium t-butoxide ki THF or DMSO at room temperature, offers an alternative procedure to selenox-ide elimination. An advantage appears to be the formation of the volatile side product dimethyl selenide, rather than the selenenic, seleninic, or selenoic acids... 

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