Sulfur trioxide, selenium

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. 

Sulfur [7704-34-9] S, a nonmetallic element, is the second element of Group 16 (VIA) of the Periodic Table, coming below oxygen and above selenium. In massive elemental form, sulfur is often referred to as brimstone. Sulfur is one of the most important taw materials of the chemical industry. It is of prime importance to the fertilizer industry (see Fertilizers) and its consumption is generally regarded as one of the best measures of a nation s industrial development and economic activity (see Sulfur compounds Sulfurremoval and recovery Sulfuric acid and sulfur trioxide). 

Tellurium burns in air with a greenish-blue flame. The combustion product is dioxide, Te02, the most stable oxide of the metal. Tellurium also forms other oxides the monoxide, TeO, the trioxide, TeOs, and the pentoxide, Te205. Monoxide has not yet been obtained in solid form. Like sulfur and selenium, tellurium forms oxyacids. Such oxyacids include orthotelluric acid, HeTeOe and tellurous acid, H2Te03, in which the metal is in +6 and +4 valence states respectively. 

Solid sulfur trioxide exists in two well-defined modifications. Orthorhombic y-SOs consists of cyclic trimers (Figure 12.38a)/ which are converted by traces of water to the one-dimensional polymeric structure of monoclinic jl-SOi, (Figure 12.38b). In contrast, selenium trioxide forms a cyclic tetramer (Figure 12.38c). ... 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

In Group VIA (16) the same phenomenon is encountered. Selenium trioxide is thermodynamically unstable relative to sulfur trioxide and tellurium trioxide. The enthalpies of formation of SF6, SeF6, and TeFft are -1210. — 1117, and — 1320 kj mol 1, respectively. This indicates comparable bond energies for S—F and Te—F bonds (317 and 330 kj mol-1, respectively), which are more stable than Se—F bonds (285 kj mol 1). 

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. 

The colored solutions produced on dissolving elemental selenium in sulfuric acid were first observed by Magnus in 1827 80). Since then a number of workers have investigated the nature of selenium solutions in sulfuric acid, oleum, and sulfur trioxide, providing 81) a substantial amount of data but little understanding of the system. Recently, it has been shown that these solutions contain the yellow Se and green Seg " polyatomic cations 82). 

Oxidation of 3,5-dialkylpyridines. 3,5-Dialkylpyridines are oxidized to pyridine-3,S-dicarboxylic acids in very good yields by sulfur trioxide or oleum when catalyzed by I-4 % selenium. 

The species, SeJ and TeJ, appear to be square-planar like whose similarity is supported by theoretical calculations that treat all of them as 6-ir electron systems.The yellow selenium cation is obtained by treating elemental selenium with fluorosulfuric acid, fuming sulfuric acid, sulfur trioxide, disulfuric acid, or antimony pentafluoride. The red tellurium cation is obtained simi-larly. = ... 

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. 

Selenosulfur trioxide, SeSO, is formed when selenium is dissolved in fuming sulfuric acid or in sulfur trioxide. It forms a green solution. 

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