Tellurium compounds organic derivatives

Te2Fio, and oxide fluorides, e.g. TeFjOTeFs, are also formed during the fluor-ination of tellurium oxides, tellurium, organic derivatives Tellurium forms organic derivatives in the +2 and +4 slates. The +2 compounds are similar to divalent sulphur derivatives although less stable. Tellurium(IV) derivatives are comparatively unstable. 

In contrast to the cathodic reduction of organic tellurium compounds, few studies on their anodic oxidation have been performed. No paper has reported on the electrolytic reactions of fluorinated tellurides up to date, which is probably due to the difficulty of the preparation of the partially fluorinated tellurides as starting material. Quite recently, Fuchigami et al. have investigated the anodic behavior of 2,2,2-trifluoroethyl and difluoroethyl phenyl tellurides (8 and 9) [54]. The telluride 8 does not undergo an anodic a-substitution, which is totally different to the eases of the corresponding sulfide and selenide. Even in the presence of fluoride ions, the anodic methoxylation does not take place at all. Instead, a selective difluorination occurs at the tellurium atom effectively to provide the hypervalent tellurium derivative in good yield as shown in Scheme 6.12. 

Orthotelluric acid is a crystalline, well-characterized compound. All the hexavalent tellurium compounds discussed in this chapter are derivatives of orthotelluric acid. Telluric acid (H2Tc04), corresponding to sulfuric acid, is not known. Organic derivatives of such a telluric acid similar, for instance, to dimethyl sulfate, are also unknown. 

Organic tellurium compounds with one Te—C bond containing divalent, tetravalent, or hexavalent tellurium have been prepared. The most widely investigated and best characterized compounds are the diorgano ditellurium derivatives and the organo tellurium trihalides. Pentafluoroethyl tellurium chloride tetrafluoride is the only known example of a hexavalent tellurium compound with one Te-C bond in the molecule. 

Quite a large number of organic tellurium compounds with a C —Te —S or a C-Te —Se unit have been prepared. Most of the compounds are rather stable towards atmospheric agents. The low molecular mass compounds have a tendency to convert to diorgano ditellurium and diselenium derivatives. 

The class of organic tellurium compounds with two Te —C bonds contains divalent, tetravalent, and hexavalent tellurium derivatives. 

Unsymmetrical diorgano tellurium compounds are formed when diorgano ditellurium derivatives are reacted with an equimolar amount of an organic lithium compound or a Grignard reagent. 

Diorganyl mono- and ditellurides are the best-known classes of organic tellurium compounds comprising symmetric and unsymmetric alkyl, aryl, and alkyl-aryl tellurides. In addition to acyclic tellurides, heterocychc aliphatic telluroethers as well as aromatic tellurophene-derivatives are known (for a review, see Ref 36). 

The diorgano tellurium dicarboxylates are white, crystalline materials that are soluble in organic solvents and stable towards atmospheric agents. Diaryl tellurium diacetates can be boiled in water without decomposition. However, bis[trifluoromethyl] tellurium bis trifluoroacetate] was reported to be moisture-sensitive. Aqueous sodium hydroxide converts diaryl tellurium dicarboxylates to diaryl tellurium oxides or dihydroxides . Thermal gravimetric analysis of diaryl tellurium dicarboxylates indicated that these compounds lose carbon dioxide at 240-260° and form the tetraaryl tellurium derivatives. The tetraorgano tellurium compounds decompose slowly to the diaryl tellurium compounds and hydrocarbons. ... 

Hypervalent iodine(III) compounds have found wide application for the oxidation of organic derivatives of nitrogen, sulfur, selenium, tellurium and other elements. Reactions of X -iodanes with organonitrogen compounds leading to the electron-deficient nitrenium intermediates and followed by cyclizations and rearrangements (e.g., Hofmann rearrangement) are discussed in Section 3.1.13. Several other examples of oxidations at a nitrogen center are shown below in Schemes 3.168-3.170. 

In the form of CdS Sei selenium is used as a red pigment in glass and ceramics. Below its melting point, Se is a semiconductor. Tellurium is used as an additive (<0.1%) to low-carbon steels in order to improve the machine qualities of the metal. This accounts for about half of the world s consumption of tellurium. Catalytic applications are also important, and other applications stem from its semiconducting properties, e.g. cadmium telluride has recently been incorporated into solar cells (see Box 14.3). However, uses of Te are limited, partly because Te compounds are readily absorbed by the body and excreted in the breath and perspiration as foul-smelling organic derivatives. 

Although progress in the chemistry of Se-N and Te-N compounds has been slower, there have been impressive developments in the last 10 years. Significant differences are apparent in the structures, reactivities and properties of these heavier chalcogen derivatives, especially in the case of tellurium. In addition, the lability of Se-N and Te-N bonds has led to applications of reagents containing these reactive functionalities in organic synthesis and, as a source... 

For books, see (a) S. Patai (ed), The Chemistry of Sulphinic Acids, Esters and their Derivatives, Wiley, Chichester, 1990 (b) D.H. Reid, Organic Compounds of Sulfur, Selenium, and Tellurium, vol 2, The Chemical Society Burlington House, London, 1973. 

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