Thallium oxide phase

Crystal growth of these compounds is complicated by the high volatility of thallium oxides and thallium-containing compounds at elevated temperatures and the toxicity of thallium. Also, the similarity in structures leads to problems controlling phase purity and samples which appear to be single crystals based on their morphology can be shown to be complicated intergrowths by X-ray diffraction studies. 

It was found that at pH > 11 in the region of low anodic overpotentials the product of thallium oxidation on an inert substrate represents the individual phase of a mixed-valence oxide which was previously unknown [352,253]. On a copper substrate, this same phase can be formed simultaneously with thallium cuprate, while at the higher overpotentials the amounts of both products in the deposit prove to be small due to the preferential formation of TI2O3 which proceeds at a high rate. At anodic overpotentials that are not too high, the rations of the amount of thallium cuprate to that of the mixed oxide in the deposits grown on copper correlates with the rate of active dissolution of copper [354], i.e., cuprate is preferentially formed at the higher pH. 

Thallium, unlike the lighter metals in the series, forms both a univalent and triva-lent ion that are stable in aqueous solution. The univalent ion Tl forms an oxide phase according to reaction (2.13) (M = Tl, x = 0.5). 

Data for the thermodynamic parameters of thallium species (both thallium(I) and thallium(III) are listed in Table 13.28). Also listed in the table are thermodynamic data for Tl", TP" and Tl(s) taken from Bard, Parsons and Jordan (1985). The table also contains thermodynamic data reported by Bard et al. for the oxide phases of thallium and some hydrolysis species. There is good agreement between the data presented by Bard et al. for Tl20(s) and those accepted in the present review. However, there is much poorer agreement for the hydrolysis species of thallium(I) and the oxide phase of thallium(III). 

Properties. Thallium is grayish white, heavy, and soft. When freshly cut, it has a metallic luster that quickly dulls to a bluish gray tinge like that of lead. A heavy oxide cmst forms on the metal surface when in contact with air for several days. The metal has a close-packed hexagonal lattice below 230°C, at which point it is transformed to a body-centered cubic lattice. At high pressures, thallium transforms to a face-centered cubic form. The triple point between the three phases is at 110°C and 3000 MPa (30 kbar). The physical properties of thallium are summarized in Table 1. 

Isobutylene oxide is produced in a way similar to propylene oxide and butylene oxide by a chlorohydrination route followed by reaction with Ca(OH)2. Direct catalytic liquid-phase oxidation using stoichiometric amounts of thallium acetate catalyst in aqueous acetic acid solution has been reported. An isobutylene oxide yield of 82% could be obtained. 

Much of the experience gained in the field of solution-phase oxidative deprotection of cysteine peptides can be applied to solid-phase chemistry. For this purpose the iodine, thallium(III), and chlorosilane/sulfoxide procedures have been usually employed,163 107-1121 generally, the results obtained with the thallium(III) reagent are better than with iodine. 

Within weeks after superconductivity was observed above 77 K in the Bi-Sr-Ca-Cu-O system, Sheng and Hermann (3) reported a record-high Tc value of 120 K for a Tl-Ba-Ca-Cu-O phase. The results were quickly confirmed (4)-(9) and the existence of a large family of thallium-containing superconducting oxides was revealed (10). 

The layer-type structures and chemical nature of the constituents of the bismuth and thallium-based cuprate superconductors - notably the lone-pair stereochemistry of Bis+, variable valence of copper, and considerable exchange among some of the cation sites - combine to make structural non-ideality, nonstoichiometry, and phase intergrowth the rule rather that the exception in these families of materials. These features, as well as the probable metastability of the phases (and possibly all high-temperature oxide superconductors), also contribute to the difficulties typically encountered in preparing single-phase samples with reproducible properties and compositions. 

Jones reagent (1, 142-143).1 Phenols substituted by at least one alkyl group in the ortfio-position can be oxidized to / -quinones by a two-phase (ether/aqueous Cr03) Jones oxidation. Yields range from 30 to 85%, but the process is simple and more economical than use of Fremy s salt or thallium(III) nitrate. 

Not only compositions containing all the HTSC metal components, but also simpler subsets, may be considered as the precursors. Thus, by a combined technique [189], Ba-Ca-Cu films were obtained by electrodeposition and then thallium was introduced from the vapor phase in the course of simultaneous oxidation. In [190, 191], it was shown that reproducible preparation of Bi-Pb cuprates can be achieved when three-component precursors are deposited and the alkaline earth cations are then introduced before annealing. It is practically impossible to provide reproducible deposition of five-component precursors. Two-stage electrosynthesis of HBCCO [200] included the intermediate annealing of a Ba-Ca-Cu deposit followed by mercury electrodeposition on the resulting oxide substrate. 

Oxidation of olefins. Kabbe explored briefly the oxidation of cyclohexene, styrene, and o-allylphenol and expressed the view that thallium triacetate is intermediate between lead tetraacetate and mercuric acetate. Anderson and Winstein followed the oxidation of cyclohexene in acetic acid at room temperature (several days) by vapor-phase chromatography and accounted quantitatively for all the five products formed the cij-and rrans-diacetates (1 and 2), the ring-contracted diacetate (3) and aldehyde (4), and the product of allylic oxidation (5). In dry solvent the transdiacetate (2) predominated, and in moist solvent the cis-diacetate (I) predominated. 

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