Tellurium compounds, fluorination

C09-0129. Tellurium compounds, which are toxic and have a hideous stench, must be handled with extreme care. Predict the formula of the tellurium-fluorine molecule or ion that has the following molecular geometry (a) bent (b) T-shaped (c) square pyramid (d) trigonal bipyramid (e) octahedron and (Q seesaw. 

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. 

E. Se202Fg, Te202F8, and Other Tellurium-Oxygen-Fluorine Compounds... 

When tetraalkoxy tellurium compounds were fluorinated in fluorotrichloromethane at — 78° with fluorine diluted by nitrogen, several alkoxy tellurium fluorides were formed, the identity of which were established by 19F-NMR spectroscopy1. The reactions were carried out as described on page 123. 

Tris[4-methylphenyl] bismuth difluoride fluorinated diaryl tellurium compounds in benzene solution2 3. 

Sihcon and boron bum ia fluorine forming siUcon tetrafluoride [7783-61-17, SiF, and boron trifluoride [7637-07-2] respectively. Selenium and tellurium form hexafluorides, whereas phosphoms forms tri- or pentafluorides. Fluorine reacts with the other halogens to form eight interhalogen compounds (see Fluorine compounds, inorganic-halogens). 

Stable noble-gas compounds have no industrial uses as of this writing but are frequently utilized in laboratories as fluorinating and oxidizing agents. Xenon difluoride and xenon tetrafluoride are relatively mild oxidative fluorinating agents and have been used for the preparation of phosphoms, sulfur, tellurium. 

Nitrogen and sodium do not react at any temperature under ordinary circumstances, but are reported to form the nitride or azide under the influence of an electric discharge (14,35). Sodium siHcide, NaSi, has been synthesized from the elements (36,37). When heated together, sodium and phosphoms form sodium phosphide, but in the presence of air with ignition sodium phosphate is formed. Sulfur, selenium, and tellurium form the sulfide, selenide, and teUuride, respectively. In vapor phase, sodium forms haHdes with all halogens (14). At room temperature, chlorine and bromine react rapidly with thin films of sodium (38), whereas fluorine and sodium ignite. Molten sodium ignites in chlorine and bums to sodium chloride (see Sodium COMPOUNDS, SODIUM HALIDES). 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

This review is conceived as a progress report. It includes only compounds of selenium and tellurium with the element directly bonded to fluorine. The chemical literature of the last 10 years, including 1979, has been searched thoroughly, and emphasis has been placed on facts rather than on interpretation. There are some earlier reviews covering the same area "Fluorine Compounds of Selenium and Tellurium 1970 (40), "Inorganic Selenium Chemistry 1975 (48), and "Inorganic Chemistry of Tellurium 1975 (53). 

Oxidative Fluorination of Sulfur-, Selenium-, and Tellurium-Containing Compounds... 

In its general chemical behaviour, selenium occupies an intermediate position with respect to sulphur and tellurium. It combines directly with many elements, e.g. oxygen, hydrogen, fluorine, chlorine, bromine and most metals.9 Details of some of its compounds will be given later,... 

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