Oxidation Of Tellurium Research Articles

Kinetics and mechanism of ruthenium(III)-catalysed oxidation of tellurium(IV) by alkaline diperiodatonickelate(IV)

The kinetics of RuIII-catalysed oxidation of tellurium(IV) by alkaline diperiodatonickelate(IV) were studied spectrophotometrically using a rapid kinetic accessory. The reaction is a two stage process. In both the stages, the reaction is first-order with respect to [oxidant] and to [catalyst] with an apparent less than unit order, each in [substrate] and [alkali]. Periodate has a retarding effect on the reaction rate. A mechanism involving monoperiodatonickelate(IV) (MPN) as the reactive oxidant species is proposed. The data suggest that oxidation proceeds via formation of a complex between the active species of RuIII and TeIV, which then reacts with 1 mol of MPN in a slow step to yield the products. The reaction constants involved in the mechanism were evaluated. There is good agreement between the observed and calculated rate constants under varying experimental conditions for both the stages of reaction. The activation parameters for the slow step were calculated and discussed.

Kinetic and Mechanistic Aspects of Redox Reactions of Tellurium(Iv) and Tellurium(Vi)

Many kinetic and mechanistic studies are reported on the direct and transition metal ion catalysed oxidation of tellurium(IV) with oxidants like persulphate, periodate, chromium(VI), hexacyanoferrate(III), cerium(IV), manganese(III), cobalt(III) etc. Similar studies on the reduction of tellurium(VI) by different reductants are much fewer. An attempt has been made to discuss in brief up-to-date information available on the nature of tellurium(IV) and tellurium(VI) species as well as kinetic and mechanistic studies on the direct and catalysed oxidation and reduction reactions of tellurium(IV) and tellurium(VI) respectively. The majority of reactions concerned with the oxidation of tellurium(IV) to tellurium(VI) seems to prefer a complementary path to a non-complementary one, in accordance with Schaffer's principle of equivalent change.

ChemInform Abstract: Kinetics and Mechanism of Iridium(III) Catalyzed Oxidation of Tellurium(IV) by Cerium(IV) in Sulfuric Acid Medium.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Kinetics and mechanism of iridium(III) catalysed oxidation of tellurium(IV) by cerium(IV) in sulfuric acid medium

Kinetics and mechanism of iridium(III) catalysed oxidation of tellurium(IV) by cerium(IV) in sulfuric acid medium

Production of dimethyl telluride and elemental tellurium by bacteria amended with tellurite or tellurate

AbstractThe purpose of this study was to determine whether a facultative anaerobe, Pseudomonas fluorescens K27, would produce dimethyl telluride when anaerobic cultures were amended with differing concentrations of sodium tellurate and/or sodium tellurite and how that volatile organotellurium production varied over time. Batch bacterial bioreactor experiments were undertaken in order to observe the changes in the headspace of a growth medium solution inoculated with P. fluorescens and amended with tellurium salts. Gas samples were taken from the bioreactor every hour and were analyzed by capillary gas chromatography using fluorine‐induced chemiluminescence detection to determine compounds in the headspace. Liquid samples were analyzed by spectrophotometer to determine optical densities, which were used as an indicator of cell growth. Verification of the identity of the dimethyl telluride produced in the bacterial headspace above a tellurate‐amended culture was achieved by comparison with the chromatographic retention time of an authentic (CH3)2Te standard and by gas chromatography/mass spectrometry. The time course production of dimethyl telluride varied with amendment salts' tellurium oxidation states and concentrations. Increasing tellurate concentrations caused slower bacterial growth, but those cultures reached the stationary phase sooner than cultures amended with tellurite concentrations 10 or 100 times less. Black elemental tellurium (Te0) was produced by live cultures amended with tellurium salts but not by sterile controls. The amount of tellurium in the solid phase (as Te0 and in/or on cells) harvested from replicate, anaerobic cultures of P. fluorescens sampled after 92 h of incubation was approximately 34%. Mixed tellurite/tellurate amendment experiments exhibited a synergistic toxic effect and yielded less final biomass and very little dimethyl telluride production compared with cultures amended with either tellurate or tellurite alone. Copyright © 2001 John Wiley & Sons, Ltd.

Internal oxidation of an Ag-1.3 at.% Te alloy

The internal oxidation of Ag–1.3 at.% Te was studied at 750, 800, and 830°C in pure oxygen (1 atm). The internal oxidation under such high oxygen pressure resulted in formation of two different types of oxide particles and two different fronts of internal oxidation in the internal oxidation zone. The coarser Ag2TeO3 particles were formed through the in situ internal oxidation of Ag2Te particles and the tiny oxide precipitates (most probably also Ag2TeO3) were formed through internal oxidation of tellurium from solid solution. Considering the mechanism of internal oxidation, both diffusionless and diffusive modes were found to be present simultaneously in the oxidation of Ag–1.3 at.% Te alloy. These results were examined with regard to the solubility of tellurium in silver, which was found to be 0.1 at.% Te at 750°C and 0.26 at.% Te at 830°C, as well as the presence and dissolution of Ag2Te particles.

Osmium(VIII) catalyzed oxidation of tellurium(IV) by periodate in aqueous alkaline medium

Osmium(VIII) catalyzed oxidation of tellurium(IV) by periodate in alkaline medium is found to occurvia oxidant-catalyst complex formation in a slow step followed by the interaction of substrate and complex in the fast step to yield the products with regeneration of catalyst. One of the products, Te(VI), considerably retards the rate of reaction. The reaction shows zero order in [tellurium(IV)], first order each in [IO4] and [Os(VIII)] and an inverse fractional order dependence on [OH]. A plausible mechanism is proposed and the reaction constants involved in the mechanism are derived.

Kinetics and Mechanism of Oxidation of Tellurium(IV) by Alkaline Diperiodatonickelate(IV)

The kinetics of oxidation of tellurium(IV) (Te(IV)) by diperiodatonickelate(IV) (DPN) in aqueous alkaline medium has been studied spectrophotometrically. The reaction exhibits first order in [DPN] and fractional order both in [Te(IV)] and [OH-]. Periodate has a retarding effect on the rate of reaction. Effects of added products, ionic strength and dielectric constant of the reaction medium have been investigated. A mechanism involving the monoperiodatonickelate( IV) (MPN) as the reactive species of the oxidant has been proposed. The constants involved in the mechanism are obtained. There is a good agreement between the observed and calculated rate constants. The activation parameters are computed with respect to the slow step of the mechanism.

Thermal and photo-induced surface damage in paratellurite

Long-term operation of TeO2 acousto-optical device is limited by the formation of surface damage caused by the He–Cd laser irradiation. Similar surface damage occurs during the heat treatment of the TeO2 crystal at 350°C. In this study, TeO2 specimens after various surface treatments have been observed by electron microscopy and X-ray photoelectron spectroscopy. The variation of the transmittance for mechanically polished specimens has been measured in situ during heat treatments. It was found that the thermal surface damage at 350°C was formed in the surface layer damaged by mechanical polishing. The mechanically damaged layer was amorphous and deficient in oxygen in the as-polished state. The electron microscopic observation revealed that the surface damage layer induced by heat treatments or by the ultraviolet light irradiation contained tellurium particles (20–40 nm) in diameter dispersed in the TeO2 matrix. On annealing the TeO2 specimen at 500°C in air, however, the particles disappeared because of the melting, evaporation and oxidation of tellurium which restores the transmittance of the crystal. Based on the results, combined with the observation of surface damage induced by the visible light irradiation, a possible mechanism of the surface damage formation has been briefly discussed.

Solid-state tellurium-125 nuclear magnetic resonance studies of transition-metal ditellurides †

Solid-state 125Te NMR studies of inorganic compounds containing tellurium in oxidations states ranging from –II to VI have been made. The chemical shift tensors of Te(OH)6, TeCl4, TeO2 and elemental tellurium have been determined by simulation of magic angle spinning (MAS) NMR spectra. Binary transition-metal ditellurides have been studied by MAS and static 125Te NMR techniques. The observed MTe2 NMR shifts range from ca. 500 to 8000 ppm [from aqueous Te(OH)6] and are shown to be correlated with the expected tellurium oxidation state. Separation of the chemical shift and Knight shift contributions has been attempted.

Simultaneous oxidation and stripping for separating Se and Te from sulfur

Sulfur as a potential by-product of hydrometallurgical processes contains selenium and tellurium as impurities. These impurities have to be removed if the sulfur is to be marketable. While selective reduction of selenium from sulfur is not realized, the selective oxidation of selenium and tellurium from sulfur in acidic solutions can be achieved provided that proper contact of selenium and tellurium with the oxidant is available. Simultaneous oxidation and stripping has been employed to separate selenium and tellurium from the sulfur in this study.

Kinetics and Mechanism of Oxidation of Tellurium(IV) by Periodate in Alkaline Medium

Kinetics and Mechanism of Oxidation of Tellurium(IV) by Periodate in Alkaline Medium

A Cyclic Voltammetric Study of the Dissolution of Tellurium

A cyclic voltammetric study of the oxidation and reduction of elemental tellurium over the pH range 0-14 has been undertaken with tellurium disk electrodes which could be rotated. In both oxidation and reduction, the behaviour of tellurium is largely that expected from the predictions of the E-pH diagram for this element. Exceptions to this general principle were observed during the oxidation of tellurium at both low and high pH where it was found that tellurous acid was relatively quick to form and slow to dissolve; this led to a type of passivation behaviour. On the reduction side, the system behaved in a complex, fashion between pH 8 and 11 with both HTe - and Te22- being formed.

ChemInform Abstract: Oxidation of Tellurium by Molybdenum and Uranium Hexafluoride in Acetonitrile and Reactions Between Uranium Hexafluoride and Dichlorine or Hydrogen Chloride in Acetonitrile.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Oxidation of tellurium 'by molybdenum and uranium hexafluoride in acetonitrile and reactions between uranium hexafluoride and dichlorine or hydrogen chloride in acetonitrile

Reactions between elemental tellurium and UF 6 or MoF 6 at room temperature lead to the isolation of solid products formulated as [Te IVF 3(NCMe) 2][M VF 6][M VF 5(NCMe)] 3 (MMo or U) on the basis of their spectroscopic properties. In contrast, oxidation of Te by SbF 5, AsF 5 or the [NO] + cation in MeCN appears to be limited to the formation of the [Te 4] 2+ cation. Uranium hexafluoride is reduced to [UF 5(NCMe)] in the presence of Cl 2 or HCl in MeCN, the reduction being followed by Cl-for-F exchange to give [UF 5− x Cl x (NCMe)] mixtures. A rationalization of these reactions is presented.

The reaction of some substituted ortho-benzoquinones with elemental tellurium and with tellurium(II) compounds

The oxidation of elemental tellurium by three ortho-benzoquinones (RO2: R = Cl4C6, Br4C6 or 3,5-But2H2C6) is a direct route to the corresponding tellurium(IV) catecholates Te(O2R)2. The analogous reaction with organotellurium(II) TeR′2[R′= Me2, Et2, Ph(Et) or Ph(Br)] gives the products Te(O2R)R′2. The reactions proceed in each case by one-electron transfer, since the presence of the semiquinone radical RO2˙ in the reaction mixture has been demonstrated by ESR spectroscopy. The Te(O2R)2 species resist further oxidation, and also show weak donor and acceptor properties. The structure of the compound Te(O2C6H2But2-3,5)2(bipy)1(bipy = 2,2′-bipyridine) has been determined by X-ray crystallography. Crystal parameters: triclinic, space group P, a= 10.388(2), b= 14.468(3), c= 15.820(3)Å, α= 106.00(1), β= 115.98(2), γ= 94.98(2)°, Z= 2 and R= 0.0424 for 3424 reflections. For Te(O2C6Cl4)·18-crown-6 2(18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane), the crystal parameters are: monoclinic, space group P21/n, a= 10.809(4), b= 18.571(7), c= 19.287(9)Å, β= 91.53(4)°, Z= 4 and R= 0.057 for 3768 reflections. In 1 the bipy is co-ordinated by weak Te–N interactions, with clear evidence for a stereochemically active lone pair, while in 2 the cryptand ring is situated around the axis of the presumed lone pair.

A Polymeric Tellurium Cation by Oxidation of Tellurium with Tungsten Bromides

The polymeric tellurium cation [Te] in Te7WOBr5 is made up of almost planar Te7 units, which are linked to form a folded band (see Figure). Related structural motifs were hitherto only known in the case of tellurium polyanions. Te7WOBr5 can be obtained by oxidation of tellurium with a WOBr4/WBr5 mixture.

Improved synthesis of Te 6(AsF 6) 4, and TeF 3·AsF 6

▪ Original preparation of Te 6(AsF 6) 4 1 involved the reaction of elemental tellurium with excess AsF 5 for several days followed by a tedius and not totally complete separation from Te 4(AsF 6) 2. The present method involves the oxidation of tellurium with AsF 5 in the presence of traces of Br 2 in SO 2 at r.t. (eq. 1). The sparingly soluble Te 6(AsF 6) 4 is easily separated from other side products, TeF 4 and TeF 3·AsF 6 as they are highly soluble in SO 2. TeF 3·AsF 6 was detected by NMR in the solutions of TeF 4 and excess AsF 5 in SO 2 2. The present preparation of TeF 3AsF 6 (eq. 2) is effected in a simple one step, without the prior preparation of TeF 4, which is prepared by the reaction of TeO 2 and SF 4 at high pressure 3. The method has been extented (eq. 3) to give TeF 4 but needs careful removal of traces of TeF 3·AsF 6. Te + AsF 5 ▪ TeF 4 + 2 AsF 3 (3)

Anodic polarization of HgTe, CdTe and Hg0.8Cd0.2Te ? Oxide formation kinetics and composition

A comparative study of the anodic polarization behaviour of HgTe, CdTe and Hg0.8Cd0.2Te at constant current density was undertaken. It is argued that metal dissolution starts first, which renders the semiconductor surface negatively charged and tellurium rich. The process continues until the overpotential across the interface rises sufficiently to dissociate the tellurium at which point tellurium dissolution and oxidation begins. The continuation of this process evidently requires that the metal dissolution follows. This dissolution-precipitation mechanism for oxide nucleation is supported here. It is predicted that the molar ratio of HgTeO3 to CdTeO3 in the anodic oxide on Hg0.8Cd0.2Te should be ∼1.1. This is in good agreement with the experiments. The overvoltages required to initiate oxidation are shown to decrease when the current density is increased.

Te, a New Tellurium Polycation

Te8[WCl6]2 is formed upon oxidation of tellurium with WCl6. In the crystal the bicyclic Te cation is associated to give chains (see 1) and can be regarded as a tellurium polycation [Ten]n/4⊕ Such polycations were already postulated almost 20 years ago by R. J. Gillespie, but up to now they have never been structurally characterized.