Tellurides reductions

Tellurium 2.1 221 Nagyagite (mixed sulfide and telluride) Reduction of ore with S02... 

On the other hand, the triflate 254 was treated with sodium azide, followed by reduction of the lactone carbonyl function, and subsequent mesylation, complete removal of the protecting groups and reprotection by EtsSiCl, to afford 259 (Scheme 25). Sodium hydrogen telluride reduction of the azide function in 259 followed by intramolecular double cyclization with sodium acetate afforded the bicycle 260, which on deprotection furnished 261 in 45% overall yield from the triflate 254. 

Lead Telluride. Lead teUuride [1314-91 -6] PbTe, forms white cubic crystals, mol wt 334.79, sp gr 8.16, and has a hardness of 3 on the Mohs scale. It is very slightly soluble in water, melts at 917°C, and is prepared by melting lead and tellurium together. Lead teUuride has semiconductive and photoconductive properties. It is used in pyrometry, in heat-sensing instmments such as bolometers and infrared spectroscopes (see Infrared technology AND RAMAN SPECTROSCOPY), and in thermoelectric elements to convert heat directly to electricity (33,34,83). Lead teUuride is also used in catalysts for oxygen reduction in fuel ceUs (qv) (84), as cathodes in primary batteries with lithium anodes (85), in electrical contacts for vacuum switches (86), in lead-ion selective electrodes (87), in tunable lasers (qv) (88), and in thermistors (89). 

When sulfuryl chloride was used in this reaction instead of POCI3 or PCI3, imidoyl chlorides 17 were isolated as the products (89KGS120). By reduction of 17 with Na2S205 aryl methyl tellurides 18 are formed which readily eliminate a molecule of methyl chloride to give 2-arylbenzotellurazoles 12 (R = Ar) in 40-65% yields. 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in... 

The electrochemical behavior of single-crystal (100) lead telluride, PbTe, has been studied in acetate buffer pH 4.9 or HCIO4 (pH 1.1) and KOH (pH 12.9) solutions by potentiodynamic techniques with an RRDE setup and compared to the properties of pure Pb and Te [203]. Preferential oxidation, reduction, growth, and dissolution processes were investigated. The composition of surface products was examined by XPS analysis. It was concluded that the use of electrochemical processes on PbTe for forming well-passivating or insulating surface layers is rather limited. 

When the conditions are controlled properly, Zn can mediate the reduction of the C-C double bond of a, (3-unsaturated carbonyl compounds in the presence of a nickel catalyst in aqueous ammonium chloride (Eq. 10.7). The use of ultrasonication enhances the rate of the reaction.15 Sodium hydrogen telluride, (NaTeH), prepared in situ from the reaction of... 

A more extensive and detailed study of these reactions (i. e. 32 to 33) was carried out by Dabdoub et al., who found that two equivalents of Cp2Zr(H)Cl are needed for complete consumption of acetylenic tellurides 35 (Scheme 4.24) [51]. Solubilization of Cp2Zr(H)Cl in the reaction medium (THF) is apparently not a sufficient indication of educt consumption when only 1.1 equivalents are employed (e. g., following a proton quench, 58% of the product 37 and 41% of the acetylenic telluride 35 were recovered). Furthermore, care must be taken to avoid Cp2ZrH2, potentially present following the Buchwald route [3] to Cp2Zr(H)Cl, since Csp—Te bond reduction can occur to a significant extent in the presence of this dihydride or of residual LAH. 

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. 

Several other oxidation reactions of selenoxides and telluroxides are summarized in Fig. 23. Ley, Barton, and co-workers discovered that di-4-methoxyphenyltellur-oxide (54) could be used catalytically as an oxidant in the presence of 1,2-dibromotetrachloroethane. After reduction of the telluroxide to the telluride, the di-4-methoxyphenyltelluride (24) debrominated the 1,2-dibromotetrachloroethane to give the tellurium(IV) dibromide, which was hydrolyzed in situ to give the telluroxide 54. This process was used to oxidize phosphines to phosphine oxides and... 

Sodium hydrogen telluride is prepared by reduction of tellurium with NaBH4 under several conditions. The original procedure uses ethanol as the solvent, adding, after complete reduction of the tellurium, an appropriate amount of acetic acid (see Section 4.1.2, ref. 10 Section 4.1.7, ref. 29). 

The tellurolate anion formed can be alkylated in situ, giving alkyl aryl tellurides, if the above reaction is effected in the presence of a phase transfer catalyst. Otherwise, performing the reaction in the presence of the reducing agent TUDO a telluride yield near to quantitative is generated, owing to the reduction of the aryl tellurinate anion to aryl tellurolate. ... 

Reduction of diaryltellurium dichlorides with sodium ascorbate (typical procedure). Bis (p-methoxyphenyl)tellurium dichloride (0.20 g, 0.48 mmol) dissolved in acetone (10 mL) was added to a stirred solution of sodium ascorbate (0.20 g, 1.0 mmol) in water/methanol (2+8 mL). After 24 h, water (50 mL) and CH2CI2 (50 mL) were added and the two phases separated. The organic phase was dried (CaCl2) and the solvent evaporated in vacuo. Flash chromatography yielded 0.14 g (84%) of bis(p-methoxyphenyl) telluride. 

Elemental tellurium, treated with strong aqueous alkali, undergoes an oxido-reduction disproportionation giving the corresponding telluride ion which reacts with acetylenes to give divinylic tellurides in modest yields. ... 

Alkyl- and aryltellurols generated in situ by the well-established reduction of ditellurides with NaBH /EtOH add to terminal acetylenes, giving (Z)-vinylic tellurides. "" ... 

The divinylic ditellurides, obtained as described, are converted into alkyl vinyl tellurides by reduction with AILiH4 followed by alkylation. ... 

The reduction of acetylenic tellurides to the vinylic ones is achieved by treatment with NaBH4 in EtOH. The formal unusual reduction of the carbon triple bond by NaBH4 can be rationalized involving the attack of a hydride ion to the tellurium atom producing a tellurol and an acetylenic anion followed by the addition of the tellurolate anion to the acetylene, DIBAL-H has later been employed as a reducing agent. ... 

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