Tellurium elimination

In contrast to 2//-chromenes 61 (M = O) (66JA5931), thia- (M = S) (68JPC997) and selenachromenes 61 (M = Se) (73TL2007), on UV irradiation, undergo reversible valence isomerization to quinoneallydines 61a 2//-tellurachromene 61 (M = Te) eliminates tellurium and converts to indene under the same conditions (90UP1). 

The second method employed for the synthesis of telluraxanthene is similar to that widely used for the preparation of various tricyclic heterocycles containing one or two heteroatoms. It is based on the interaction of 2,2 -dilithiodiphenylmethane with powdered tellurium, by which reaction telluraxanthene 82 has been prepared in 50% yield [81JOM(205)167]. The reaction apparently proceeds through the intermediate bis(telluro-phenolate) 86 which is oxidized to the heterocyclic ditelluride 87. The latter compound eliminates tellurium from its stericaily strained seven-membered ring and converts to telluraxanthene. This mechanistic scheme seems to be corroborated by the observation that the treatment of lithi-oarenes ArLi usually ends in the formation of diarylditellurides Ar2Te2 (74MI1 83MI2). 

Diorgano ditellurium compounds eliminate tellurium on heating to form the corresponding diorgano tellurium. These reactions begin above 200° in the absence of a solvent but proceed in good yields only above 300°8. Less stable substrates, e.g., bis[3-methoxyphenyl]... 

The acetal from 1,2-dihydroxyethane and bis[benzoylmethyl] tellurium eliminated tellurium from the molecule upon treatment with p-toluenesulfonic acid in dry acetone or with traces of sulfuric acid in wet acetone11. 

Bis[benzoyImethyl] tellurium dichloride eliminates tellurium in a photon-induced reaction7. This process is the basis for the use of bis[benzoylmethyl] tellurium dichloride as a component in photo-imaging systems. Dibenzyl tellurium dihalides deposit tellurium on standing at 20°8. 

A solution of 2-phenyltellurophene in diethyl ether kept in a Pyrex container eliminates tellurium upon irradiation with light from a 300 nm lamp and produces 1-phenylbut-l-yn-3-ene8. 

The tellurazepine eliminated tellurium on heating in xylene to give a phenanthridine derivative1. 

The tellurepin (29) spontaneously eliminates tellurium over 2-3 days in solution at room temperature to give naphthalene in a manner similar to borepins and benzophosphepines <91CC802>. Higher temperatures (about 200 °C) are required to eliminate selenium from (30) <72JHC1427> and from (19) <84JHC1321> to give the aromatic products (31) and (32), respectively. 

The unusual physical complaints and findings in workers overexposed to teUurium include somnolence, anorexia, nausea, perspiration, a metallic taste in the mouth and garlic-like odor on the breath (48). The unpleasant odor, attributed to the formation of dimethyl teUuride, has not been associated with any adverse health symptoms. Tellurium compounds and metaboUc products have been identified in exhaled breath, sweat, urine, and feces. Elimination is relatively slow and continuous exposure may result in some accumulation. No definite pathological effects have been observed beyond the physical complaints outlined. Unlike selenium, teUurium has not been proved to be an essential biological trace element. 

Tellurium-chilled kon has been used in mining, automotive, railroad, and other equipment. Tellurium used as a coating for molds and cores, so-called corewashes, eliminates troublesome localized shrinkage in castings. These corewashes may contain ca 25% tellurium the remainder consists mainly of siUca and some bentonite. 

A treatment of 2-butyltelluroaniline with an equimolar amount of bromoacetic acid results in spontaneous cyclization of the formed telluronium salt 31 to give 1-butylbenzotellurazinonium bromide 30. That the alkylation occurs at the tellurium and not at the nitrogen atom of 2-butyltelluroaniline has been proved by the isolation of the methyl ester of 31 in 60% yield when the amine was coupled with methyl bromoacetate under the same reaction conditions. Elimination of butyl bromide from 30 readily occurs on heating of its DMF solution leading to 2//-l,4-benzotellurazin-3(4//)-one 32 in 90% yield. 

The compound 92 is extremely light-sensitive. Under the action of phosphites or compounds with multiple bonds, it readily eliminates a tellurium atom and thus may be considered as a synthetic equivalent of the heterodiene 93a. 

On treatment with sodium ethanolate or aqueous ethanolic KOH, 2,5-diaza-1,6-dioxa-6<2-tellurapentalenes 97 eliminates a tellurium atom to give l,2,3-triketone... 

Tellurium sources, 22-24 Thermodynamics in cyclo-oligomerization, 185-186 butadiene insertion, 187-188 reductive elimination, 193, 194 selectivity control, 212 polysilane isomerisation, 158-160 see also Stability Thermolysis, 135, 136, 158 THF (tetrahydrofuran), 97, 150, 153 Thio-Wittig reaction, 37 Tin, 121... 

In the tellurium(IV) oxidation state, the 5p orbital of the tellurium(fV) atom is involved in the three-center, four-electron bonding to the halides and cannot interact with the carbon rr-framework. Long-wavelength absorption maxima for 6-11 are found between 515 and 565 nm in dichlromethane. Reductive elimination generates the tellurium(II) oxidation state in compounds 12 and 13. The tellurium(II) 5p orbital can now overlap with the carbon 7r-framework and long-wavelength absorption maxima for 12 and 13 are observed between 765 and 830 nm in dichloromethane. The rate of loss of the 515-565 nm band and the rate of appearance of the 765-830 nm band are identical, which is consistent with reductive elimination as the rate-determining step of this process. 

Fig. 2 Reductive elimination of halogens from chalcogenopyrylium dyes 6-11 containing tellurium(IV) dihalide groups. 

The transfer of iodine to the organic substrate represents a formal reductive elimination at tellurium(lV) to give tellurium(ll) as well as oxidation of the alkene. In a series of diaryltellurium(lV) diiodides, iodination of organic substrates is accelerated by electron-withdrawing substituents and is slowed by electron-donating substituents, which is consistent with the substituent effects one would expect for... 

Enriched or should be used for the reactor irradiation to eliminate unwanted background radiations from the other tellurium isotopes. Radiation damage to the source is unimportant since annealing (13) the ZnTe after irradiation did not change line intensity or width. 

Diaryl ditellurides are relatively thermolabile compounds and eliminate one tellurium atom by heating at 300°C. ° In the presence of copper metal, however, the extrusion of tellurium is achieved during reflux with toluene or dioxane. " " ... 

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