Redoxkinetik von Metallkomplexen in nichtwäßrigen Lösungen,XI. Die Reduktion von Thallium(III)oxinat mit Eisen(II) in schwach koordinierenden Lösungsmitteln

The kinetics of the iron(II) reduction of thallium(III) oxinate does not differ essentially from that of the oxinate-transfer from thallium(III)-oxinate to iron(III), described before: formation of a binuclear intermediate, rearrangements within, and subsequent reaction with the excess reactant to the final products. As for the redox process, these intermediates are binuclear Tl(II)-Fe(III) complexes which, with initial reactants, form further complexes in which the second electron is transferred. In the cases of excess Tl(ox)₃ and of equimolar reactants, disproportionations are likely involved.     

Sequential oxidimetric determination of thallium(I) and (III)

The reaction between thallium(III) and oxalic acid in sulphuric acid medium has been investigated. Spectrophotometric results show that thallium(III) can be quantitatively reduced to thallium(I) with oxalic acid in aqueous medium when heated to near boiling point. Conditions for the estimation of the excess of oxalic acid with cerium(IV) sulphate in the presence of thallium(I) and for the estimation of a mixture of thallium(I) and thallium(III) have been investigated. The method is simpler than many other redox methods reported for the determination of thallium(III) and is free from many interferences encountered in these titrations. The reagents are cheap and quite stable.     

Extraction separation of thallium (III) from thallium (I) with n-octylaniline

A novel method is developed for the extraction separation of thallium(III) from salicylate medium with n-octylaniline dissolved in toluene as an extractant. The optimum conditions have been determined by making a critical study of weak acid concentration, extractant concentration, period of equilibration and effect of solvent on the equilibria. The thallium (III) from the pregnant organic phase is stripped with acetate buffer solution (pH 4.7) and determined complexometrically with EDTA. The method affords the sequential separation of thallium(III) from thallium(I) and also commonly associated metal ions such as Al(III), Ga(III), In(III), Fe(III), Bi(III), Sb(III) and Pb(II). It is used for analysis of synthetic mixtures of associated metal ions and alloys. The method is highly selective, simple and reproducible. The reaction takes place at room temperature and requires 15-20 min for extraction and determination of thallium(III).     

Radiation induced exchange reaction between thallium(I) and thallium(III)—Comparison of sulfuric acid and perchiloric acid solution

The rate constant of radiation induced exchange reaction between thallium(I) and thallium(III) ions has been studied for elucidating the mechanisms which are responsible for (T1(II) intermediates or bridging groups (SO ₄ ^2– ) in sulfuric acid and perchloric acid solutions. It was found that the radiation induced exchange reaction is accelerated by the sulfate ion, and the rate of the thallium(II)-thallium(I) reaction is faster than that of the thallium(II)-thallium(III) process in perchloric acid solution.     

Ruthenium(III)-catalyzed oxidation of thallium(i) by 12-tungstocobaltate(III) in hydrochloric acid medium

The reaction between thallium(I) and [Co^IIIW₁₂O₄₀]^5- in the presence of ruthenium(III) as catalyst proceeds viainitial outer-sphere oxidation of the catalyst to ruthenium(VI). The ruthenium(IV) thus generated will oxidize thallium(I) to an unstable thallium(II) which by reacting with oxidant gives the final product, thallium(III). The formation of ruthenium(II) by direct two-electron reduction of the catalyst by thallium(I) is thermodynamically less favorable. The reaction rate is unaffected by the [ H⁺ ], whereas it is catalyzed by chloride ion . The formation of reactive chlorocomplex,TlCl, in a prior equilibrium is the reason for the chloride ion catalysis. Increasing the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer-sphere complex between the catalyst and oxidant. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetik und Mechanismus des Ligandentausches zwischen Thallium(III)oxinat und Eisen(III) in Propylencarbonat

The transfer of oxinate ions from thallium (III)oxinate to trivalent Fe(DMF) ₆ ³⁺ in propylenecarbonate takes place via rearrangements within a rapidly formed binuclear thallium(III)—iron(III) complex. In a last rapid step this rearranged complex reacts with excess reactants to the final products whose composition accordingly depends on the ratio of the reactant concentrations.

     

Kinetics of the oxidation of cyclohexene by thallium(III) acetate

The kinetics of the reaction by which thallium(III) acetate oxidizes cyclohexene in glacial acetic acid medium, has been studied by UV spectrophotometric observation at 30°C. The consumption of thallium(III) acetate follows a second-order rate law exhibiting first-order dependence on each of thallium(III) acetate and cyclohexene; however, the first-order dependence on cyclohexene disappears at high cyclohexene concentrations as pseudo-first-order conditions prevail above 0.2 M cyclohexene. A steady-state model of the following form is proposed: where Tl, Cy, and Com are units of Thallium(III) acetate, cyclohexene, and a reaction complex. The value of k₂ has been evaluated as 0.00027 and (k_?1 + k₂) as 0.0385k₁. For low thallium(III) acetate concentrations the reaction kinetics follow the rate law: where α = the excess concentration of cyclohexene over thallium(III) triacetate. For thallium(III) acetate concentrations above 0.02 M, double salt formation of thallium(III) acetate with product thallium(I) acetate removes thallium(III) acetate from the reaction and a modified rate law is observed. Runge–Kutta numerical solutions to the differential equations provide confirmation that the rate expressions are valid in predicting the observed concentrations of thallium(III) acetate.     

The determination of thallium(III) with the 2,2'-bipyridyl-iron(II) chelate

A spectrophotometric determination of thallium (III), based on solvent extraction of an ion-association pair formed between the cationic 2,2'-bipyridyl-iron(II) chelate and the anionic thallium(III) bromide complex is described. The best extractant is 1,2-dichloroethane and extraction is possible over the pH range 2.5–6.7. The composition of the extracted species was confirmed, and conditions were established for the extraction over the concentration range 7.9·10^-6–3.5·10^-5M of thallium in aqueous solution.     

Studies on the potentiometric thallium(III)-selective carbon paste electrode and its possible applications

Construction, performance characteristics and applications of a carbon paste thallium(III) ion-selective electrode are described. The electrode, which is based on ion-associate compounds formed between cetylpyridinium and chlorothallate(III) complexes dissolved in tricresyl phosphate as pasting liquid, showed near-Nernstian response over the concentration range of 5.8 x 10(-6) - 2.9 x 10(-3) mol/L. Potentiometric titrations of thallium(III) with cetylpyridinium chloride were affected by higher concentrations of excess halides, probably due to the formation of higher halogenothallates.     

Influence of thallium(I) and thallium(III) on parameters of oscillating chemical reaction in a bromate-cerium(III,IV)-malonic acid-sulfuric acid system

The influence of thallium(I) and thallium(III) on the parameters of the Belousov-Zhabotinskii oscillating chemical reaction in the bromate-cerium(III, IV)-malonic acid-sulfuric acid system was studied. As a result of the addition of thallium(I) and thallium(III), the oscillation parameters change in the same way, which cannot be explained by the complexation of these ions with the bromide only. It was found that during the oscillating reaction, thallium(I) can be oxidized by bromine-containing compounds and thallium(III) reduced by the transformation products of malonic and bromomalonic acids. A scheme of action of a thallium(III)/thallium(I) two-electron redox pair in the oscillating chemical reaction studied has been proposed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 1, pp. 106–111, January–February, 1987.     

Direct potentiometric determination of tin(II) and (IV), antimony(III), thallium(III), rhenium(VII), and bismuth(III) with cetylpyridinium chloride

Summary The precipitation titrations of the following elements vs. cetylpyridinium chloride were investigated: Rhenium as perrhenate, tin as the (II) and (IV) species, antimony(III), thallium(III), and bismuth(III) as their halogen complexes. Optimum conditions for the determinations are described. Of the elements examined only thallium(III) also could be titrated potentiometrically vs. tetraphenylarsonium chloride. Titrations were monitored with a simple sensor consisting of a graphite rod coated with poly(vinyl chloride) and dioctylphthalate, and a double-junction reference electrode.

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Direkte potentiometrische Bestimmung von Zinn(II) und (IV), Antimon(III), Thallium(III), Rhenium(VII) und Bismut(III) mit Hilfe von Cetylpyridiniumchlorid

Zusammenfassung Die Fällungstitration der genannten Elemente mit Cetylpyridiniumchlorid wurde untersucht: Re als Perrhenat; Zinn in 3- und 4wertiger Form; Sb(III), Tl(III) und Bi(III) in Form ihrer Halogenkomplexe. Die optimalen Bedingungen werden mitgeteilt. Nur Thallium(III) kann auch potentiometrisch gegen Tetraphenylarsoniumchlorid titriert werden. Die Titrationen werden mit Hilfe eines einfachen Sensors kontrolliert, der aus einem mit Polyvinylchlorid und Dioctylphthalat überzogenen Graphitstab besteht sowie einer double-junction Bezugselektrode.

     

Determination of thallium(I) in solutions containing cations interfering in potentiometric ion-pair formation-based titrations

The possibility of the use of simple potentiometric coated-wire sensors in the analysis of mixtures of ions, the determination of which is based on the ion-pairing principle, was studied. Attention was especially paid on the determination of thallium(I) in the presence of alkali metal ions, mercury(II), copper(II) and silver(I). It was found that thallium(I) can selectively be titrated with sodium tetraphenylborate in diluted solutions. Interferences of ions of the alkali metals are practically negligible if their concentrations are lower than 10(-3) mol dm(-3). Interference of Cu(II) is minimized using EDTA as a masking agent, Hg(II) and Ag(I) ions are sufficiently screened by additions of sodium cyanide. In mixtures containing higher concentrations of alkali metals, thallium(I) can be oxidized to thallium(III) and selectively titrated as TlCl(-)(4) with a cationic titrant.     

Studies on the potentiometric thallium(III)-selective carbon paste electrode and its possible applications

Construction, performance characteristics and applications of a carbon paste thallium(III) ion-selective electrode are described. The electrode, which is based on ion-associate compounds formed between cetylpyridinium and chlorothallate(III) complexes dissolved in tricresyl phosphate as pasting liquid, showed near-Nernstian response over the concentration range of 5.8 × 10^–6– 2.9 × 10^–3 mol/L. Potentiometric titrations of thallium(III) with cetylpyridinium chloride were affected by higher concentrations of excess halides, probably due to the formation of higher halogenothallates.     

Vanadium(III) as an analytical reagent: The titrimetric determination of iron, copper, thallium, molybdenum, uranium, vanadium, chromium and manganese

Vanadium(III) solutions can be used in direct titrations of iron(III), copper(II), thallium(III), molybdenum(VI), uranium(VI), vanadium(V), chromium(VI) and manganese(VII) in milligram amounts. The titrations are done at 70-80 degrees for iron(III), copper(II), thallium(III), molybdenum(VI) and at room temperature for vanadium(V), chromium(VI) and manganese(VII). Uranium(VI) is titrated at 70-80 degrees in presence of iron(II). The vanadium(III) solution is prepared by reduction of vanadium(V) to vanadium(IV) with sulphur dioxide, followed by addition of phosphoric acid and reduction with iodide, and is reasonably stable.     

Voltammetric determination of thallium(I) at a mechanically renewed Bi-graphite electrode

A composite of high-purity grade carbon powder and an epoxy resin is used to in situ obtain a bismuth-film electrode. The surface of the indicator electrode is renewed by cutting a thin surface layer before each determination. The in situ obtained Bi-film electrode is virtually no different from an Hg-film electrode in sensitivity, reproducibility, and the ability to separate signals from Tl, Cd, and Pb. The calibration graph is linear in the range of thallium concentrations from 0.01 to 1 mg/L (RSD varies from 4 to 2%). A significant excess of Pb(II), Sn(II), and Cd(II) does not interfere with the determination of thallium. A procedure for determining down to 5 × 10^?6% thallium in lithium carbonate is developed.     

Studies with dithizone : Part 26. The interaction of thallium(III) with solutions of dithizone in organic solvents

The strong oxidising capacity of thallium(III) dominates its reaction with solutions of dithizone (H₂Dz) in organic solvents. When carbon tetrachloride is used as solvent, the unstable thallium(III) complex Tl(HDz)³ is found in the organic phase but it very quickly disproportionates to the thallium(I) complex [Tl(HDz)], and bis-1,5-diphenylformazan-3-yl-disulphide. This reaction is notably faster in chloroform, in which thallium(I) dithizonate is the first identifiable product. In contact with an acidic aqueous phase, thallium(I) dithizonate is reverted to regenerate dithizone in the organic phase and Tl⁺ ions appear in the aqueous phase. Organic solutions of the disulphide disproportionate spontaneously by first-order kinetics to give an equimolar mixture of dithizone and the mesoionic compound, 2,3-diphenyl-2,3-dihydrotetrazolium-5-thiolate: this change is much slower in carbon tetrachloride than in the more polar chloroform and is catalysed by both Tl⁺ and Tl³⁺. If thallium(III) is present in excess, the mesoionic compound is the principal oxidation product of the dithizone although a dication may also be formed. The mesoionic compound does not react with thallium(I) but forms a water-soluble 2:1 complex with thallium(III); partition of this complex into the organic phase is uninfluenced by chloride ions. Because of the large number of competing reactions, the composition of the reaction mixture at any stage of the reaction between thallium(III) and dithizone depends on the relative concentrations of the components, the order in which they are brought together, the time elapsed after mixing, the pH of the aqueous phase, and the nature of the organic solvent.     

Mutual binary separations of cadmium(II), indium(III) and thallium(III) as chlorides by their extraction in high molecular weight amines

The extraction of cadmium(II), indium(III) and thallium(III) with high molecular weight amines have been studied from aqueous hydrochloric acid solutions. Using the data mutual binary separations of these three elements with high separation coefficients are proposed. Various variables like type of amine, amine concentration and organic diluent were explored to propose the best conditions of separations.     

Niobium(III) as an analytical reagent. : Part I. The titrimetric determination of iron,copper, thallium,molybdenum, uranium and vanadium

Niobium(III) solutions can be used in direct titrations of copper(II), iron(III), thallium(III), moIybdenum(VI), vanadium(V) and uranium(VI) in milligram amounts. Phenosafranine is generally satisfactory as the indicator, but potentiometric end-points can also be used. Copper and iron can be determined successively when a mixed indicator containing phenosafranine and méthylene blue is used. Thallium(I) and thallium (III) can be determined in mixtures. The niobium (III) solutions are stable for several days under a carbon dioxide atmosphere.     

Thallium(II) in the chemically induced thallium(I)-Thallium(III) exchange

The rate of the electron exchange between thallium(I) and thallium(III) induced by iron(II) has been measured at various concentrations of Tl(I), Tl(III), and Fe(II).²⁰⁴Tl tracer, initially in the Tl(I) state, was used. Exchange induced by the separation method was less than 0.01%. The mechanism earlier discussed is $$\begin{gathered} Tl^{III} + Fe^{II} \rightleftharpoons Tl^{II} + Fe^{III} \left( {k_1 ,k_{ - 1} } \right) \hfill \\ Tl^{II} + Fe^{II} \rightharpoonup Tl^I + Fe^{III} \left( {k_2 } \right) \hfill \\ *Tl^I + Tl^{II} \rightleftharpoons *Tl^{II} + Tl^I \left( {k_I } \right) \hfill \\ *Tl^{II} + Tl^{III} \rightleftharpoons *Tl^{III} + Tl^{II} \left( {k_{III} } \right), \hfill \\ \end{gathered} $$ which provides an exchange path in addition to the two-electron reaction^*Tl^I+Tl^III?^*Tl^III+Tl^I (k_ex). The rate law deduced from this mechanism agrees with experiment over a limited range of conditions but fails to account for the observed effect at low concentrations of Tl(I). The additional rate can be represented by inclusion of a term in which the rate of the induced exchange is independent of the concentration of Tl(I). When treated according to the resulting complete rate law the data are consistent with earlier photochemical studies. The present results in combination with other data give k₂=3·10⁶ M^?1·sec^?1 in 1M perchloric acid at 25°C. This is in satisfactory agreement with a recent pulse radiolysis measurement as well as with independent flash photolysis studies.     

Effects of some surface-active substances on polarographic waves of thallium(I), lead(II), antimony(III) and uranium(VI) in acetate medium: Determination of Thallium with Electrochemical Masking by Dioctyl Sulphosuccinate

The effects of some surface-active substances on the polarographic waves of Tl(I), Pb(II), Sb(III) and U(VI) in an acetate medium are described. The shifts observed in half-wave potentials offer several possibilities for the selective polarographic determination of these species. A method for the determination of thallium(I) in the presence of large amounts of Sb(III) and U(VI) and commensurate amounts of Pb(II). with dioctyl sulpho-succinate, is proposed.