Ditellurides oxidation

Data on the electrochemistry of the telluride ion in alkaline media are relatively limited. Mishra et al. [53] studied the oxidation of Te to Te° at solid electrodes, focusing on the intermediate step(s) of this process, and in particular, the possibility of detecting ditelluride Te via rotating ring disk electrode (RRDE) methodology. Oxidation beyond the elemental state to TeO and TeO was also studied using cyclic and hydrodynamic voltammetry. 

It was observed in other works that in sulfide electrolyte, decomposition of ZnSe was still obtained stable PECs could be constructed though from singlecrystal, n-type, Al-doped ZnSe electrodes and aqueous diselenide or ditelluride electrolytes [124]. Long-term experiments in these electrolytes were accompanied by little electrode weight loss, while relatively constant photocurrents and lack of surface damage were obtained, as well as competitive electrolyte oxidation. Photoluminescence and electroluminescence from the n-ZnSe Al electrodes were investigated. 

It has, however, also been reported that the reaction of aryl ditellurides with Ni°, Pd°, and Pt° may result in the cleavage of the carbon-chalcogen bond. The oxidative addition of... 

Diorgano diselenides have been used extensively as precursors to seleninic acids in the presence of hydrogen peroxide.The catalytic activity of preformed seleninic acids and seleninic acids generated in situ are identical. Diorgano ditellurides have also been used as catalysts in thiolperoxidase-like reactions for the oxidation of thiols with various peroxides. However, tellurinic acids are not thought to be involved even though RTe(=0)SPh types of structures are proposed as intermediates. 

Only half of the tellurium of the starting ditelluride is converted into telluride. The other half, converted into tellurolate, can be oxidatively recovered as the starting ditelluride. 

The Grignard route to diorganyl ditellurides suffers from lack of generality and the mechanism of the oxidation seems to be uncertain. Alkylmagnesium halides demonstrate lack of reactivity towards elemental tellurium/ whereas aryhnagnesium halides in ether as the solvent furnish a mixture of ditellurides and tellurides. Satisfactory results are obtained by tellurium insertion in aryhnagnesium halides in THF followed by oxidation before or after aqueous work-up. ... 

Air is then bubbled through it to oxidize the lithium tellurolate. The red oily ditelluride that separates is extracted with ethyl ether (200 mL). The organic phase is washed with H2O (2X50 niL), dried (CaCl2) and evaporated to give 2.83 g of a viscous red oil. Distillation of 5.66 g of the crude material prepared in this manner affords 4.87 g of pure di-n-butyl ditelluride (89% based on Te b.p. 103-105°C/0.8 torr). 

Di-2-thienyl and di-2-furyl ditelluride are prepared from thiophene and furan by lithia-tion with n-buthyllithium, tellurium insertion and oxidative work-up. 

Di-2-thienyl ditelluride (typicalprocedure) n-Butyllithium (ll.OmL, 2.2 M, 24.2 mmol) is added to an ice-cooled stirred solution of thiophene (2.0 g, 23.8 mmol) in dry THF (50 mL). After 10 min at 0°C and 50 min at room temperature, elemental Te (2.9 g, 22.7 mmol) is added rapidly. All Te is completely dissolved after 30 min, when the yellowish solution is poured into a beaker containing H2O (300 mL). CH2CI2 (200 mL) is then added and air passed through the two-phase system for 1 h. To effect complete oxidation, the beaker is left overnight in the open air. The organic phase is separated and the aqueous phase extracted several times with CHjClj. The combined organic extracts are dried (CaCy and evaporated to give a red solid. Recrystallization from EtOH affords 3.54 g (74%) of di-2-thienyl ditelluride (m.p. 89-90°C). 

The direct oxidation of lithium aryl tellurolates into the ditellurides without previous aqueous work-up is exemplified by the preparation of di(2,4,6-tri-t-butylphenyl) ditel-luride. ... 

The arylation of sodium teUuride in NMP (see Section 3.1.2.1) followed by air oxidation gives rise to diaryl ditellurides in medium to good yields. 

Divinylic ditellurides (generalprocedure) Elemental Te (12.7 g, 100 mmol) is added at once to a stirred solution of the vinylic magnesium bromide (0.11 mol) in THE (150 mL) under N2. The mixture is refluxed for 30 min with stirring, allowed to reach room temperature, then stirred for 1 h in the presence of air (by opening the apparatus). Deposition of some Te is observed during the oxidation process. The mixture is treated with brine. 

Method G (typical procedure). NaBH, (5%) in 5% aqueous NaOH, is added dropwise under N2 to a solution of 5a, 6)3-dibromocholestan-3)3-ol (1.50 g, 2.73 mmol) and bis(2-thienyl) ditelluride (0.10 g, 0.24 mmol) in EtOH (20 mL) at room temperature until the red colour of the ditelluride disappears. Air is then introduced to the system to oxidize the catalyst to the ditelluride. The mixture is diluted with ether and H2O, and the organic phase is washed with H2O, dried and evaporated. Chromatography of the residue on SiOj (eluting with CH2Cl2/MeOH, 95 5) furnishes cholesterol (0.95 g (90%) m.p. 149-150°C). 

The observation that the previously described diacetoxylation of olefins by means of tel-lurinic anhydrides produces quantitative yields of the corresponding ditellurides suggested the oxidative functionalization of olefins employing diphenyl diteUuride combined with an oxidizing agent instead of the tellurinic anhydride. ... 

The by-product of the elimination, phenyltellurenic acid, is detected, at least partly, as diphenyl ditelluride, and is probably formed by disproportionation and oxidation reactions. 

It was also demonstrated that acute exposure to diphenyl ditelluride did not change [ H]glutamate release and uptake by rat brain synaptosomes. In contrast, in vitro experiments indicate that 100 am of diphenyl ditelluride clearly inhibit [ H]glutamate uptake by brain synaptosomes and synaptic vesicles. These results also suggested that the inhibitory effect on glutamate uptake may be related, at least in part, to the ability of this compound to oxidize thiol groups. ... 

Diselenides, MSe2, and ditellurides, MTe2 (M = Th, U, Pu), are known but the oxidation state of the metal in these compounds is uncertain. Other selenides and tellurides [e.g. Th2Se5, USe3, MTe3 (M = Th, U) and UTe5] are presumably analogous to the actinide(IV) polysulfides (p. 1135). A more detailed description of these systems is available.139... 

Lithium tris(trimethylsilyl)silyltellurolate bis(tetrahydrofuran) is a pale yellow, air-sensitive solid that is soluble in hydrocarbons, diethyl ether, and THF. The finely powdered solid oxidizes (sometimes pyrophorically) in air to give the dark green ditelluride (SiMe3)3SiTeTeSi(SiMe3)3.8 The lithium tellu-rolate is dimeric in the solid state as shown by X-ray crystallography10... 

The filtrate from the iodide on evaporation in a desiccator yields a colourless crystalline solid (1 3 grams). Extraction with small quantities of hot water gradually removes any remaining iodide, a white powder remaining as residue. This is an anhydride of methyl hydroocytellurium oxide (telluracetic acid), CH3.TeO.OH, which cannot be obtained pure. In aqueous solution it is neutral to litmus, gives no precipitate with silver nitrate, and is reduced by potassium bisulphite to dimethyl ditelluride. It has a persistent odour, and gradually blackens above 230° C. 

Acidification of (35) gives the highly stable tellurol (Me3Si)3SiTeH as an air-sensitive wax, with pKa 7.3, which readily oxidizes to the ditelluride and gives base-free derivatives of the alkali metal with (Me3Si)2NM (M = Li, Na) or KOBu-t31. 

The presence of a 3-methyl group in 53 changes the reaction course. When the oxidant Se02 is used in more than twofold excess relative to 3-methyl-2//-tellurachromene, bis[2-(3 -propene-2 -methyl-1 -al)phenyl]-ditelluride 56a is formed in 60% yield. When a smaller relative amount of Se02 is used in this reaction, aldehyde 56a is formed along with the product of selenium insertion into the Te—Te bond, 58 (in 15% yield [83JOM(258)163]. 

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). 

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