Selenium, tetra-,

After investigating the action of liquid ammonia on a variety of selenium compounds, Streeker and Claus 5 have come to the conclusion that the tetrahalides are the best initial materials for the preparation of selenium nitride. The action of liquid ammonia on selenium tetra-bromide in the presence of carbon disulphide gives a good yield of the nitride. 

Important results and a detailed insight into aqueous chemical deposition processes have been reported and discussed elsewhere for CdSe [248, 249] and ZnS [250, 251] target products. We should note also the work of Davies et al. [252] who described an alternative method for the chemical growth of metal sulfides and selenides on the basis of polysulfide or polyselenide solutions (containing hexa- and tetra-chalcogen anions) formed by the dissolution of sulfur or selenium in hydrazine monohydrate. ... 

No selenium(VI) is extractable from citrate buffered solution containing EDTA and copper. Therefore, tetra- and hexavalent selenium could be determined separately. 

Sulphur, selenium and tellurium are soluble in the oxychloride in the cold, but on heating, reaction may take place. Sulphur interacts to form selenium monochloride, sulphur monochloride and sulphur dioxide. Tellurium is converted into its tetrachloride. Both red and yellow phosphorus react violently with the oxychloride, forming phosphorus pentoxide and selenium mono- and tetra-chlorides. Carbon, silicon and boron are unattacked. 

The sulfide group forms a large number of complexes where it is in chelation with a different heteroatom. Among the common heteroatoms are N, P and As. These complexes are too numerous to list here, but individual complexes can be found from Table 9 or from refs. 1224 and 1667. It is also possible to synthesize compounds which will form bi-, tri- and tetra-dentate complexes to platinum(II), where sulfur, selenium and tellurium.are the only atoms which coordinate to the metal. A review of complexes formed from ligands of the type RS(CH2) SR has been recently published.1734 This article outlines the synthesis, reactions and spectroscopy of these complexes, and allows the complexes of platinum to be placed in context with those of other transition metals. 

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... 

The reaction of tetrachlorodisilane with chalcogenation reagents is one of the synthetic methods to bis-nor-adamantane or double-decker type compounds. When a solution of di-terf-butyltetrachlorodisilane 66 in THF is refluxed together with one equivalent of lithium sulfide or stirred with lithium selenide at room temperature, the tetra(ferf-butylsilicon)pentachalcogenides 67 and 68, respectively, are formed (Scheme 18)6. Each pentachalcogenide exhibits one resonance of a ferf-butyl group in the H and 13C NMR spectra. Most likely, the bis-nor-adamantane derivatives 69 and 70 are initially formed. Insertion of a sulfur or selenium atom into one of the two strained Si—Si bonds would then lead to the observed products. 

A selenium dioxide induced oxidative cyclization of the 2 -hydroxychalcone 745 is a key step in the total synthesis of ( )-5 -methoxyhydnocarin-D (Scheme 189) <2005T4149>. DMSO containing catalytic amounts of iodine also effectively promotes the oxidative cyclization of 2 -hydroxychalcones to afford flavones <1996CHEC-II>. The DMSO-iodine mediated cyclization of the bis(2 -hydroxychalcone) 746 is a key step in the synthesis of the natural atropisomer4 4 ",7,7 -tetra-O-methylcupressuflavone (Equation 298) <1997TL1087>. Likewise, silica gel supported indium(in) halides catalyze the oxidative cyclization of 2 -hydroxychalcones to afford flavones in excellent yield (Equation 299) <2005TL253>. 

This ester cannot be dehydrogenated with palladium-charcoal, selenium, or chloranil 16 similar attempts to aromatize 4,5,6,7-tetrahydrobenzo[c]thiophene have failed.616 Diethyl 4,5,6,7-tetra-hydrobenzo[c]thiophene-l,3-dicarboxylate forms an adduct with maleic anhydride.6... 

Lead tetra acetate Periodic Acid Osmium Tetraxide Selenium Dioxide Perbenzoic Acid... 

A number of reoxidants for selenium dioxide have been examined. For example, while hydrogen peroxide is sometimes successful, oxidation of cholecalciferol (27) or derivatives widi selenium dioxide alone gave poor results not improved by addition of hydrogen peroxide. In this case, use of sodium periodate or tetra-R-butylammonium periodate gave increased yields. The reaction was much improved when carried out under reflux in methanol or solvent mixtures containing methanol, and indeed selenous acid and dialkyl selenites, suggested as intermediates in die reaction, both accomplished a similar oxidation in nonalcoholic solvents in die presence of a reoxidant, A -methylmorpholine iV-oxide proving superior. 

Selenium and tellurium reagents have been used for stereoselective halogenations of alkenes. For example, trans addition of benzeneselenenyl chloride to alkenes followed by the displacement of the seleno moie with chloride can lead to dr-1,2-dichlorides (equation 25). The addition of 2-naph-thyltellurium trichloride proceeds in an anti stereospecific manner (equation 26), whereas tellurium tetra-diloride gives a mixture of syn and anti adducts. The reaction of allyl esters with tellurium tetrachloride accompanies acyl migration to give the l-(trichloiottlluro)-3-chk>io adduct (54 equation 27). ... 

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