Selenium commercial sources

Tellurite TeOj is a rare, white or yellowish orthorhombic mineral. The principal commercial source of selenium is the slime from lead and copper refineries. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Commercial uses of Se, Te, and Po are limited, though selenium is used to make red colored glass and in photocopiers (see the Interlude at the end of this chapter). Tellurium is used in alloys to improve their machinability, and polonium (2i0po) has been used as a heat source in space equipment and as a source of alpha particles in scientific research. 

It is difficult to make stable hollow cathodes from certain elements, particularly those that are volatile, such as arsenic, germanium, or selenium. The HCLs of these elements have short lifetimes and low intensities. An alternative light source has been developed in the EDL. A commercial EDL design is shown in Fig. 6.7. A small amount of metal or a salt of the element whose spectrum is desired is sealed into a quartz bulb with a low pressure of Ar gas. The bulb is shown centered inside the coils in Fig. 6.7. The coils are part of a self-contained RF generator. When power is applied to the coils, the RF field generated will couple with the metal or salt in the quartz bulb. The coupled energy will vaporize... 

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