Tellurium compounds fluorides

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. 

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. 

SAFETY PROFILE Poison by inhalation. Human skin (systemic) effects. When heated to decomposition it emits very toxic fumes of F" and Te. See also FLUORIDES and TELLURIUM COMPOUNDS. 

Bis[t-butyldimethylsilyl] tellurium and bis[phenylethynyl] ketone in tetrahydrofuran at 20° in the presence of /-butanol and tetrabutylammonium fluoride formed five- and six-membered heterocyclic tellurium compounds. ... 

Caution. Tellurium compounds are highly toxic. They should be handled with care in a well-ventilated fume hood and treated in the same way as toxic inorganic fluorides (e.g., HF, CIF, AsF ). ... 

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. 

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. 

Ceric ammonium sulfate, 5 674 Ceric fluoride, 5 674 Ceric hydroxide, 5 676 Ceric oxide, 5 670, 675 Ceric rare earths (RE), 74 631 Ceric sulfate, 5 674 Ceric sulfate method, for tellurium determination, 24 415 Cerium (Ce), 5 670-692 74 630, 63 It, 634t. See also Cerium compounds analysis, 5 679-680 color, 7 335... 

The dialkylaminotellurium(VI) pentafluorides are pale yellow liquids that decompose rapidly above 35°C. Bis(dimethylamino)tellurium(VI) tetrafluoride is a pale yellow solid, mp 57°C. The compounds have been characterized by IR, Raman, H-NMR, 19F-NMR, and mass spectroscopy. Reaction of (RaSi)2NH with TeF6 produces RaSiNHTeF5 (mp 9°C), which can be cleaved with HF to yield aminotellurium(VI) penta-fluoride (155) [Eq. (14)]. 

A number of hexahalogenotellurates(IV) have been investigated. A few rather unstable hexafluoro complexes are known, for example the nitrosonium compounds of composition (NO)2XF6 have been obtained40 from the reaction of nitrosulfuryl fluoride, NOS02F, with selenium or tellurium tetrachloride. The selenium compound loses nitrosyl fluoride at room temperature to leave the pentafluoroselenate(lV), whereas the tellurium analogue remains... 

Tellurium hexafluoride itself has been found to form complexes with potassium, rubidium and cesium fluorides. The cesium compound has a stochiometry approaching Cs2TeF8 and, in these types of complexes, the stability of the lattice appears to be inversely related to the polarizing power of the cation and the compounds are only stable in the solid state.41 Several heptafluorotellurates(VI) have been prepared from the reaction of tellurium with chlorine trifluoride in anhydrous hydrofluoric acid followed by addition of the metal fluoride.42... 

The platinum metal chalcogenides in general are easier to prepare than the corresponding oxides. Whereas special conditions of temperature and pressure are required to prepare many of the oxides, the platinum metals react most readily with S, Se, and Te. A number of additional differences concerning the chemistry of the chalcogenides and the oxides are summarized as follows The metal—sulfur (selenium, tellurium) bond has considerably more covalent character than the metal-oxygen bond and, therefore, there are important differences in the structure types of the compounds formed. Whereas there may be considerable similarity between oxides and fluorides, the structural chemistry of the sulfides tends to be more closely related to that of the chlorides. The latter compounds... 

Pentaalkoxy tellurium monofluorides were formed by fluorination of tctramethoxy tellurium1, by reaction of m-tetramethoxy tellurium difluoride with sodium methoxide in methanol1, by the action of anhydrous hydrogen fluoride on hexamethoxy tellurium2, and by the condensation of primary alcohols with tellurium hexafluoride1. None of these compounds was isolated. Their presence in the reaction mixture was detected by 19F-NMR spectroscopy. 

Tellurium hexafluoride heated with at least 4.5 molar equivalents of a primary alcohol at 90° for 9 days in the presence of excess sodium fluoride, formed a mixture of alkoxy tellurium fluorides containing cis- and trans-tetraalkoxy tellurium difluorides1. These mixtures could not be separated by distillation. The compounds were identified by 19F-NMR spectroscopy. 

Fluorination with elemental fluorine diluted 1 20 with nitrogen was used to prepare pentafluorophenyl tellurium trifluoride from bis[pentafluorophenyl] ditellurium at — 60° with fluorotrichloromethane as the reaction medium. The yield in this reaction was 80% 4-Methoxyphenyl tellurium trifluoride was obtained by electrochemical oxidation of the diaryl ditellurium in 0.5 M hydrofluoric acid at platinum electrodes2. Bisfpentafluoroethyl] ditellurium and chlorine fluoride (1 6) reacted at — 78° to give pentafluoroethyl tellurium trifluoride, a white solid melting at 95°3. The same compound was obtained with xenon difluoride as the fluorinating agent and melted at 143°4. 

Treatment of aryl tellurium trichlorides with silver fluoride, potassium bromide, or potassium iodide causes chlorine to be exchanged for other halogens (see p. 320). The reaction of 4-ethoxyphenyl tellurium trichloride with silver acetate gave a compound of indefinite composition6. 

Diaryl tellurium dichlorides, obtainable from aromatic compounds and tellurium tetrachloride, react with excess bromine or iodine in refluxing DMF or acetonitrile in the presence of a metal fluoride to give aryl halides in low yields. The reactions with chlorinating agents are very sluggish. The reaction of bromine and bis[4-methoxyphenyl] tellurium dichloride formed 2,4-dibromomethoxybenzene in 76% yield. Reactions of these tellurium dichlorides with copper(I) cyanide in DMF produced aryl cyanides in yields of less than 8%3. 

All of these compounds are stable gases, exhibiting the maximum valency of the elements. They neither attack glass nor decompose spontaneously. The selenium and tellurium fluorides attack mercury making it adhere to glass, and m this respect they resemble (worn. Sulphur hexafluoride does not do this. 

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