Selenium dioxide sulfur trioxide

CADMIUM FUME (1306-19-0) Forms explosive mixture with aluminum, ammonium perchlorate, magnesium in the presence of heat, chlorine trifluoride. Explodes or ignites on contact with hydrazinium nitrate, hydrogen peroxide (90%), hydrogen sulfide, hydrogen trisulfide, lithium. Can increase the thermal and explosive sensitivity of nitroalkanes, hydrazinium perchlorate. May react with phosphorus, sulfur, sulfur dioxide, sulfur trioxide, selenium, zinc. 

Selenium trioxide, SeO, is white, crystalline, and hygroscopic. It can be prepared by the action of sulfur trioxide on potassium selenate or of phosphorous pentoxide on selenic acid. It forms selenic acid when dissolved in water. The pure trioxide is soluble in a number of organic solvents. A solution in Hquid sulfur dioxide is a selenonating agent. It is stable in very dry atmospheres at room temperature and on heating it decomposes first to selenium pentoxide [12293-89-9] and then to selenium dioxide. 

The chemical properties of selenium fall between sulfur and tellurium. Thus, selenium reacts with oxygen similarly to sulfur, forming two oxides, selenium dioxide, Se02 and trioxide, SeOs. The metal combines with halogens forming their halides. With nonmetals, selenium forms binary compounds exhibiting oxidation states +4 and -i-6. 

The chief advantages of the contact process are the high purity of the product and the fact that the product is a concentrated acid. Disadvantages are the high cost of the catalysts and the fact that if sulfides are used as raw materials, costly purification of the sulfur dioxide is necessary, because impurities such as arsenic trioxide and selenium dioxide poison the catalyst (i.e., render the catalyst inactive). Platinum catalysts are particularly sensitive to these impurities, while vanadium catalysts are claimed to be free from this disadvantage. 

Of the dozen or more chalcogen oxides which have been reported, only the dioxides and trioxides of sulfur and selenium will be discussed here. Other oxides of sulfur (for example, SO, S2O8, S2O7, and SO4) have been described, but these are unstable and, at present, unimportant. 

Potassium permanganate. Dimethyl sulfide-Chlorine. Dimethyl sulfoxide. Dimethyl sulfoxide-Chlorine. Dimethylsulf-oxide Sulfur trioxide. Dipyridine chro-mium(VI) oxide. Iodine. Iodine-Potassium iodide. Iodine tris(trifluoroacetate). Iodosobenzene diacetate. Isoamyl nitrite. Lead tetraacetate. Manganese dioxide. Mercuric acetate. Mercuric oxide. Osmium tetroxide—Potassium chlorate. Ozone. Periodic acid. Pertrifluoroacetic acid. Potassium ferrate. Potassium ferricyanide. Potassium nitrosodisulfonate. Ruthenium tetroxide. Selenium dioxide. Silver carbonate. Silver carbonate-Celite. Silver nitrate. Silver oxide. Silver(II) oxide. Sodium hypochlorite. Sulfur trioxide. Thalli-um(III) nitrate. Thallium sulfate. Thalli-um(III) trifluoroacetate. Triphenyl phosphite ozonide. Triphenylphosphine dibromide. Trityl fluoroborate. 

As previously noted, the high temperature of the combustion process causes the nitrogen and oxygen in the air to react to produce nitrogen oxides. The non-carbon (elements) impurities in the fuels react to form oxides sulfur dioxide is the primary hazardous product, but others such as selenium dioxide and arsenic trioxide are also produced. Mercury is released as vapor. When vented from the combustion zones this complex mixture of compounds blends with the air. Under the influence of sunlight, it continues to react to produce the complex product, smog. "... 

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