Selenium metal oxides

Oxidation reactions were used in the synthesis of porphyrin d, the metal-free ligand system of naturally occurring heme d,. In a total synthesis of porphyrin d,12d oxo functions were introduced into isobacteriochlorin 3 by selenium dioxide oxidation to yield 4. The selenium dioxide selectively attacks the 3- and 8-positions of the partially reduced pyrrole rings of the chromophore. In another synthesis23a c of porphyrin d, an isobacteriochlorin 5, derived by... 

See Metal oxides, also Non-metal oxides, both above Selenium, etc., also Sulfur, and Sulfuric acid, all below Ammonium nitrate Ammonium sulfate, etc. 

Dining attempted conversion of recovered selenium metal to the dioxide by heating in oxygen, a vigorous explosion occurred. This was attributed to selenium-catalysed oxidation of traces of organic impurities in the selenium. Oxidation of recovered selenium with nitric acid is rendered vigorous by presence of organic impurities, but is a safe procedure [1]. The later reference incorrectly attributed the explosions to the nitric acid procedure [2],... 

Templeton AS, Trainor TP, Spormann AM, Brown GE Jr (2003b) Selenium speciation and partitioning within Burkholderia cepacia biofilms formed on a-Al203 surfaces. Geochim Cosmochim Acta 67 3547-3557 Templeton AS, Trainor TP, Traina SJ, Spormann AM, Brown GE Jr (2001) Pb(II) distributions at bio film-metal oxide interfaces. Proc Natl Acad Sci USA 98 11897-11902... 

In coastal environment, detrital and authigenic Fe and Mn oxides, which accumulate in oxic surface sediments, play a pivotal role in determining the geochemical behaviour of arsenic (Mucci et al., 2000) and selenium (Belzile et al., 2000). Arsenic and selenium differ in their affinities for metal oxide surfaces. Although both adsorb onto iron oxides, arsenate (As(V)) adsorbs more strongly than arsenite (As(lll)), and selenite (Se(IV)) adsorbs more strongly than selenate (Se(VI)) (Belzile et al., 2000). 

Treatment of 73 with selenium metal at 360° yields dibenzothio-phene. Oxidation of 73 with hydrogen peroxide was accompanied by partial dehydrogenation yielding 1,2,3,4-tetrahydrodibenzothiophene 5,5-dioxide (68). ... 

Of the important properties of glass, color is one of the most interesting. Color is usually achieved by the addition of various metal oxides. The strongest of these are titanium, vanadium, chromium, manganese, selenium, iron, cobalt, nickel and copper. Silver and uranium will give weak colors. Some of the rare earths are also used as colorants with sharp absorption bands in contrast to the broad bands given by most colorants. (4)... 

The dissolution and measurement experiments start with attempts to dissolve a sample (300 yg or less) of a metal or metal compound species using the prescribed NIOSH procedure, followed by measurement using the NIOSH atomic absorption spectrometric (AAS) procedure. If 90 percent recovery of the metal is not achieved, the dissolution procedure is modified, or changed completely, to achieve 90 percent recovery. From previous studies, it is expected that the metal oxides, and selenium generally, would pose problems. The NIOSH-AAS procedures are to be evaluated also, especially when the dissolution matrix is changed. The AAS detection limits using standards are determined through the measurement of blanks. 

When selenium is heated with a metallic oxide or carbonate, a mixture of selenide and selenite is commonly obtained. At high temperatures selenium is able to displace sulphur partially from sulphides such as copper sulphide and silver sulpiride, the effect probably being due to selenium being less volatile than sulphur.10 At ordinary temperatures... 

The Selenites.—Selenious acid is a weak acid but neutralises hydroxides and carbonates witli the production of selenites. Ammonium selenite is formed by dissolving selenious acid in aqueous ammonia.3 The selenites can be obtained in an anhydrous condition by heating the metal oxides in a current of selenium dioxide vapour or with selenium dioxide in a sealed tube in the latter case the products can be obtained crystalline if the selenium dioxide is used in excess.4... 

Studies of semiconductor films have shown many facets. The properties of epitaxial films have mainly been investigated on Ge and Si, and to a lesser degree on III—V compounds. Much work, lias been done on polycrystalline II-VI films, particularly with regard to the stoichiometry of the deposits, doping and post-deposition treatments, conductivity and carrier mobility, photo-conductance, fluorescence,electroluminescence, and metal-semiconductor junction properties. Among other semiconductors, selenium, tellunum. and a few transition metal oxides have found some interest. 

Diaz-Somoano, M., L6pez-Ant6n, M.A. and Martfnez-Tarazona, M.R. (2004) Retention of arsenic and selenium during hot gas desulfurization using metal oxide sorbents. Energy and Fuels, 18(5), 1238-42. 

Chlorine trifluoride Metals Chromium trioxide Alkali metals Dichlorine oxide Oxidisable materials Nitryl fluoride Metals See Selenium, etc., below See also Non-metal oxides, above See also Sulfur, below See also Sulfuric acid, below... 

Cadmium pigments have been manufactured by both a direct calcination process and a precipitation-calcination process. In the first instance, a mixture of cadmium carbonate and sulfur (and zinc oxide and selenium if the hue to be produced requires their addition) is calcined at 520-600°C for 1-2 h. This direct calcination process is complicated by the volatility of cadmium oxide and selenium, both of which are toxic and require special handling. In the precipitation process, an alkali sulfide solution is added to a solution of cadmium and (in the case of green-shade yellows) zinc salts or to a solution of cadmium and (in the case of deep oranges, reds, and maroon) selenium metal to precipitate the appropriate compound. The precipitate is washed, dried, and calcined at 600-700°C in an inert or reducing atmosphere to convert the precipitated cubic structure to a more stable wurtzite crystal. The calcination conditions control particle size, which ranges from 0.2 to 1.0pm. 

It is well known that other non-metal oxides can react with hydrogen peroxide to form similar compounds which can be viewed as inorganic peracids. Such species include boron(III), arsenic(III) and selenium(IV). For example, selenium dioxide can be used as a catalyst for epoxidations or amine oxidations through perselenous acid (Figure 2.29).86... 

Osmium tetraoxide (osmic acid) Pentachlorophenol Perchloric acid Phosphorus pentasulfide Phosphorus pentoxide Phosphorus, red Phosphorus, yellow or white Picric acid, trinitrophenol Potassium cyanide Potassium perchlorate Potassium sulfide Potassium, metal Pyridine flammable Selenium Silver oxide Silver cyanide Sodium metal lump Sodium arsenate Sodium arsenite Sodium azide... 

Among oxi tions producing allylic alcohols or their derivatives the modem variants of selenium dioxide oxidations are by far the most popular. Systems based on metal acetates, particularly palladium tri-fluoroacetate, can be very useful and are receiving increasing attention but the Kharasch-Sosnovsky reaction, once very common for allylic oxidation, is now rarely used. Sensitized photooxidation with singlet oxygen, a very well-known procedure, is still somewhat unpredictable and has periu K received less consideration than it deserves. 

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