Of tellurides

Disubstituted isotellurazoles 1 (4-11%) and bis((3-acylvinyl)tellurides 3 (3-10%) were isolated in very low yields from the reaction mixture as the products of nucleophilic addition of telluride anion to the triple bond of the initial ethynyl ketones (83S824). This method cannot be applied to the synthesis of 3//-isotellurazoles. When a-acetylenic aldehydes were used instead of ethynyl ketones, bis((3-cyanovinyl)tellurides 4 obtained in 14-20% yields were the only products (83S824). 

Selenic acid, H2Se04, is a strong acid (/fai 2) and the solubility of its salts parallels that of the corresponding sulfates. It is formed by the oxidation of selenous acid or elemental selenium with strong oxidizing agents in the presence of water. Telluric acid, H2Te04, or tellurates are obtained by oxidation of tellurides,... 

Mishra KK, Ham D, Rajeshwar K (1990) Anodic oxidation of telluride ions in aqueous base ... 

In the case of telluranes, treatment of telluride with tert-butylhypochlorite yielded optically active chlorotellurane 39.58 Optically active fluoro-, bromo-, and iodo-telluranes were obtained from the chlorotellurane by treatment with AgF, NaBr, and Nal, respectively. Optically active spirotelluranes 40 were... 

Aryltellurium trichlorides are highly soluble in methanol and ethanol but less soluble in benzene. Diaryltellurium dichlorides exhibit inverse solubilities, being more soluble in benzene than in methanol or ethanol. These properties allow an easy separation of diaryl tellurides from diaryl ditellurides (frequently formed as by-products in the preparation of tellurides) the mixture is treated with SOjClj and the obtained mixed di- and trichlorides are separated by the appropriate solvents, and reduced back into the pure tellurides and ditellurides. 

This reaction has a general character and can be applied to the different types of telluride. The halogenation is accomplished in inert solvents (ether, benzene, dichloromethane and chloroform) and the dihatides are normally easily crystaUizable products. 

The chlorination of tellurides is more conveniently done by using, instead of chlorine (gaseous or dissolved in solvents), chlorinating reagents such as sulphuryl or thionyl chloride (Uke the chlorinolysis of ditellurides, see Section 3.5.2). 

By this procednre excess 1,2-dibromotetrachloroethane acts as a halogen source, converting a small amount of telluride into the corresponding dibromide, which is then... 

Carboxylic acids are also produced through the detellurative carbonylation of several types of telluride by treatment with carbon monoxide at atmospheric pressure and room temperature in the presence of Pd(ll) salts, in various solvents. ... 

In contrast to selenides, in the case of tellurides the donble bond geometry of the formed alkenes is markedly dependent upon the amount of oxidant employed. Thus, frany-cyclododecene is nearly the sole product of the oxidation of cyclododecyl phenyl tellnride with 1 equiv of oxidant, whereas with excess oxidant (even 2 equiv) a mixture of cis and frany-isomers is formed, in some cases the dy-isomer being the major product. ... 

It was discovered that the acetyl derivalive of iV-hydroxy-2-thiopyridone is especially suitable as a source of methyl radicals, being photolysed by irradiation with a simple tungsten lamp. On this basis, and because of the high radicophilicity of tellurides (especially anisyl tellurides), a radical exchange occurs when the reagent is irradiated in the presence of an... 

Ellis AB, Bolts JM, Wrighton MS (1977) Characterization of n-type semiconducting indium phosphide photoelectrodes stabilization to photoanodic dissolution in aqueous solutions of telluride and ditelluride ions. J Electrochem Soc 124 1603-1607... 

Hydrogen teUuride is used in preparation of telluride salts. 

Remark When syntheses are made in the presence of excess of tellurium (x = [Cd2+]/[Te2 ] - 3), CdTe nanoparticles are formed. After dodecanethiol addition and during the washing process, a black precipitate appears due to the formation of telluride oxide. It is then impossible to separate the CdTe nanoparticles from Te02 aggregates. 

Only three references to pure CD deposition of tellurides, all of them for CdTe, have been found [126-128] and therefore no column for tellurides is given here. Si02, Y2O3, andZr02, not given in the table, have also been deposited, as have Ag halides. 

CdTe has been deposited by hydrazine reduction of TeOi [17,18]. The potential of hydrazine oxidation is sufficiently negative to allow formation of telluride ... 

Most of the compounds deposited by CD have been sulphides and selenides. Apart from a very few examples of tellurides (and some related teUuride experiments) and with a very few exceptions, discussed at the end of this chapter, what is left is confined to oxides (including hydrated oxides and hydroxides and two examples of basic carbonates.) This chapter deals mainly with these oxides. In addition, as noted in Chapter 3, there are a nnmber of slow precipitations that resnlt in precipitates, rather than films, of varions other componnds, not necessarily semiconductors in the conventional sense. These potential CD reactions, briefly discnssed in Chapter 3, will be somewhat expanded on in this chapter. 

Another interesting example of the special behaviour of tellurides is provided by WTe2 and its relatives(Mar era/., 1992). WS2 and WSc2 crystallize in the layered M0S2... 

Dilution with water reverses the reaction, and heating the solution liberates sulfur dioxide. Upon being added to a solution of tellurides, tellurium forms colored polytellurides. Unlike selenium, tellurium is not soluble in aqueous sodium sulfite. This difference offers a method of separating the two elements. Like selenium, tellurium is soluble in hot alkaline solutions except for ammonium hydroxide solutions. Cooling reverses the reaction. Because tellurium forms solutions of anions, Te2-, and cations, Te4+, tellurium films can be deposited on inert electrodes of either sign. 

Electronic and Optoelectronic Applications of Tellurides. Most metal tellurides are semiconductors with a large range of energy gaps and can be used in a variety of electrical and optoelectronic devices. Alloys of the form HgCdTe and PbSnTe have been used as infrared detectors and CdTe has been employed as a gamma, ray detector and is also a promising candidate material for a thin-film solar cell. 

Whereas no other methods of synthesis of 21 and its derivatives are currently known, the nucleophilic addition of telluride anion to 1,5-diorganylpentadi-1,4-ynes may be considered a promising approach, based on the finding that sodium telluride reacts smoothly with monosubstituted alkynes, giving rise to divinyltellurides (89MI1). 

Likewise, no products of the anti-Michael addition were found in the reaction above. Compound 27 was obtained in 28% yield in the case of 1,5-diphenylpenta-l, 4-diyn-3-one (82JOC1968) when bis(ferf-butyldimeth-ylsilyl) telluride was used as the source of telluride anion. Heterocycle 22 (R1 = R2 = Ph) is also formed (in 19% yield). 

The addition of telluride anion to l-(trimethylsilyl)penta-l, 4-diyn-3-ones apparently represents a general method for the preparation of 2-substituted l-telluracyclohexa-2,5-dien-4-ones 22 (92MI3). In actual fact, the reaction of l-(trimethylsilyl)-5-phenylpenta-l,4-diyn-3-one with telluride anion affords 22 (R1 = Ph, R2 = H) in 38% yield, whereas only 12% of this compound is attained in the reaction with l-phenylpenta-l,4-diyn-3-one (87JOC3662). 

In the case of tellurides, strongly oxidizing peroxyl radicals may also undergo ET in competition, and the adduct to phosphines may be sufficiently long-lived to react further with 02 (Engman et al. 1995). 

Isotellurazoles 4 were obtained in low yields (3-11%) by the one-pot reaction of alkynyl ketones with hydroxylamino-O-sulfonic acid and K2Te in aqueous solution containing sodium acetate (83S824 87H1587). A plausible mechanism of the reaction includes formation of the oxime derivative and subsequent nucleophilic addition of telluride anion to the triple bond followed by cyclization to 4. The reaction is accompanied by the formation of telluro bis(alkenyl ketones) 5 in yields approximately equal to those of 4. When alkynyl aldehydes are used instead of ketones, the single reaction products are the tellurobis(alkenyl nitriles) 6 (83S824). 

A general method of synthesis of l-hetera-4-telluracyclohexa-2,5-dienes 90 is founded in the nucleophilic addition of telluride anion to type 91 diacetylene derivatives. The telluride dianion is prepared in situ from the elements in liquid ammonia. The reaction was carried out with methanol or mixtures with DMSO and liquid ammonia as solvents, with the following diacetylenes di(l-alkynyl)sulfides (73RTC1326), I-alkynylethynyl sulfides (75RTCI63), di(l-alkynyl)sulfones (78RTC244), and di(l-alkynyl)phosphi-noxides (75RTC92). 

The diaryl or aryl alkyl tellurides are dense yellow oils or crystalline solids, which are easier to handle than the dialkyl tellurides of similar molecular weight. Some of the diaryl derivatives are almost odorless solids. The same comments are valid for the diorganoditellurides 4, which are dark red oils (aliphatic derivatives) and dark red solids (aromatic derivatives). It is recommended that solutions of tellurides or ditellurides should not be kept in contact with air, since an amorphous white solid will form after some time. For some compounds, this reaction with oxygen is very fast. Aliphatic derivatives are more air sensitive than the aromatic ones. In view of this fact, it is recommended to bubble nitrogen into the solutions while a column or thin-layer chromatographic separation is performed. Evaporation of the solvent, however, minimizes the air oxidation. Pure liquids or solids can be handled in air with no need for special precautions, but prolonged exposure to air and to ambient light should be avoided. 

The introduction of tellurium into an organic substrate promotes functional groups transformations or presents structural features that can be used for synthetic purposes, if suitable methods to remove tellurium from the resulting structures are available. To date, four main strategies have been explored for this end, namely, the telluroxide elimination, the tellurium/metal exchange, the coupling of tellurides with organometallic species and with alkynes, and the reductive removal via free radicals. 

The removal of tellurium from organic substrates through the oxidation of tellurides to tellurium oxides followed by elimination was first described by Sharpless.234 However, soon it was observed that this reaction does not present the same attractiveness of the analogous selenoxide ry -elimination, since the tellurium version requires long heating or... 

---