Kinetics and mechanism of the oxidation of thiosulphate by hexachloroplatinate(IV)

Summary Rate constants for the oxidation of thiosulphate by hexachloroplatinate(IV) have been measured. The kinetics of the oxidation of thiosulphate follow a second-order rate law, first order with respect to thiosulphate and first order with respect to platinum(IV). The influence of pH is small. The rates are found to depend on the nature and concentration of the cations and follow the order: Cs⁺>Rb⁺>K⁺>Na⁺>Li⁺. The activation parameters calculated from the temperature studies are: H=42.9 k J mol^–1 and S=–102 JK^–1 mol^–1. A mechanism of the reaction in terms of intermediate formation of free radicals followed by the formation of tetrathionate is postulated to explain the kinetic behaviour.     

Kinetics of oxidation of sulphite by hexachloroplatinate(IV) in acidic solution

Summary The kinetics of the oxidation of sulphite by hexachloroplatinate(IV) has been studied over wide range of experimental conditions. The reaction is first-order in substrate and in platinum(IV). The rate decreases with the increase in acidity. The effect of salt and of changing dielectric constants on the reaction rate have been studied. Values of H and S have been calculated and are 26.3 kJ mol^–1 and –35.9 JK^–1 mol^–1, respectively. On the basis of experimental evidence, a two-electron reduction mechanism is proposed.     

Solubility of uranium (IV) oxide in alkaline aqueous solutions to 300°C

The solubility of carefully characterized UO₂ in pOH 1.5 and pOH 2.5 aqueous solutions has been determined from 25°C to 300°C using a flow apparatus. Data were analyzed in terms of the reaction $$UO_2 + 2H_2 O + OH^ - \rightleftharpoons U(OH); log K = - 5.86 + 32/T$$ The extreme sensitivity of both the UO₂ surface and aqueous U(IV) to oxidation is discussed.     

Osmium(VIII) catalysed and uncatalysed oxidation of aspirin drug by diperiodatocuprate(III) complex in aqueous alkaline medium: A mechanistic approach

The kinetics of oxidation of a non-steroidal analgesic drug, aspirin (ASP) by diperiodatocuprate(III)(DPC) in the presence and absence of osmium(VIII) have been investigated at 298 K in alkaline medium at a constant ionic strength of 0.10 mol dm⁻³ spectrophotometrically. The reaction showed a first-order in [DPC] and less than unit order in [ASP] and [alkali] for both the osmium(VIII) catalysed and uncatalysed reactions. The order with respect to Os(VIII) concentration was unity. The effects of added products, ionic strength, periodate and dielectric constant have been studied. The stoichiometry of the reaction was found to be 1:4 (ASP:DPC) for both the cases. The main oxidation product of aspirin was identified by spot test, IR, NMR and GC–MS. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. Activation parameters with respect to slow step of the mechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for both reactions. The catalytic constant (K_C) was also calculated for catalysed reaction at different temperatures and the corresponding activation parameters were determined.     

Coordination around thorium(IV) in aqueous perchlorate,chloride and nitrate solutions

The coordination around the thorium(IV) ion in aqueous perchlorate, chloride and nitrate solutions has been determined from large angle X-ray scattering measurements. In perchlorate solutions, where inner-sphere complexes are not formed, the first coordination sphere contains 8.0±0.5 water molecules with Th-H₂O bond lengths of 2.48₅ Å. In chloride solutions inner-sphere complexes are formed, which lead to an increase in the coordination number. In nitrate solutions the nitrate ions are bonded as bidentate ligands to the thorium ion. The bond lengths are similar to those found in crystalline hydrates of thorium nitrate. The coordination numbers found for thorium(IV) in solution are compared with previously reported values for lower charged ions of similar size.On leave from Department of Inorganic Chemistry Royal Institute of Technology S-10044 Stockholm Sweden     

Ruthenium(III) catalyzed oxidation of sulfanilic acid by diperiodatocuprate(III) in aqueous alkaline medium. A kinetic and mechanistic approach

The kinetics of ruthenium(III) catalyzed oxidation of sulfanilic acid by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of (0.50 mol dm⁻³) has been studied spectrophoto-metrically. The reaction between sulfanilic acid and DPC in alkaline medium exhibits 1: 4 stoichiometry (sulfanilic acid: DPC). The reaction is first order with respect to [DPC] and [Ru^III] and has less than unit order both in [sulfanilic acid] and [alkali]. The active species of catalyst and oxidant have been identified. Intervention of free radicals was observed in the reaction. The main products were identified by spot test and IR. Probable mechanism is proposed and discussed. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed. Thermodynamic quantities are also determined.     

A study of the kinetics and mechanism of oxidation of L-tryptophan by diperiodatonickelate(IV) in aqueous alkaline medium

The kinetics of oxidation of L-tryptophan by diperiodatonickelate(IV) (DPN) in an aqueous alkaline medium at a constant ionic strength of 0.30 mol dm⁻³ was studied spectrophotometrically. The reaction was first order in diperiodatonickelate(IV) and less than first order in tryptophan and the OH⁻ ion. The addition of periodate had no effect on the reaction, and nickel(II) produced did not influence the reaction rate significantly. An increase in ionic strength and decrease in medium permittivity did not affect the reaction rate. A mechanism involving the formation of a complex between L-tryptophan and reactive DPN species was proposed. The constants characterizing the mechanism were evaluated. The activation parameters for the slow reaction step were computed and discussed. The text was submitted by the authors in English.     

A new dinuclear Ti(IV)-peroxo-citrate complex from aqueous solutions. Synthetic,structural, and spectroscopic studies in relevance to aqueous titanium(IV)-peroxo-citrate speciation

The wide use of titanium in applied materials has prompted pertinent studies targeting the requisite chemistry of that metal's biological interactions. In order to understand such interactions as well as the requisite titanium aqueous speciation, we launched investigations on the synthesis and spectroscopic and structural characterization of Ti(IV) species with the physiological citric acid. Aqueous reactions of TiCl(4) with citric acid in the presence of H(2)O(2) and neutralizing ammonia afforded expediently the red crystalline material (NH(4))(4)[Ti(2)(O(2))(2)(C(6)H(4)O(7))(2)].2H(2)O (1). Complex 1 was further characterized by UV-vis, FT-IR, FT- and laser-Raman, NMR, and finally by X-ray crystallography. Compound 1 crystallizes in the monoclinic space group P2(1)/n, with a = 10.360(4) A, b = 10.226(4) A, c = 11.478(6) A, beta = 107.99(2) degrees, V = 1156.6(9) A(3), and Z = 2. The X-ray structure of 1 reveals a dinuclear anionic complex containing a Ti(IV)(2)O(2) core. In that central unit, two fully deprotonated citrate ligands are coordinated to the metal ions through their carboxylate moieties in a monodentate fashion. The central alkoxides serve as bridges to the two titanium ions. Also attached to the Ti(IV)(2)O(2) core are two peroxo ligands each bound in a side-on fashion to the respective metal ions. NH(4)(+) ions neutralize the 4- charge of the anion in 1, further contributing to the stability of the derived lattice through H-bond formation. The structural similarities and differences with congener vanadium(V)-peroxo-citrate complexes may point out potential implications in the chemistry of titanium with physiological ligands, when the former is present in a biologically relevant medium.     

Kinetics and mechanism of electron transfer reactions in aqueous solutions: Silver(I) catalyzed oxidation of aspartic acid by cerium (IV) in acid perchlorate medium

Silver(I) catalyzed oxidation of aspartic acid by cerium(IV) was studied in acid perchlorate medium. The stoichiometry of the reaction is represented by the eq. (i) Dimeric cerium(IV) species has been indicated and employed in calculations of monomeric cerium(IV) species concentrations. The reaction is second-order and uncatalyzed reaction also simultaneously occurs along with the silver(I) catalyzed reaction conforming to the rate law (ii) where k is an observed second-order rate constant. A probable reaction mechanism is suggested. © 1995 John Wiley & Sons, Inc.     

Manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid medium: a kinetic and mechanistic study

The manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid has been studied spectrophotometrically at 25 °C and I = 1.60 mol dm⁻³. Stoichiometry analysis shows that one mole of glycerol reacts with two moles of cerium(IV) to give cerium(III) and glycolic aldehyde. The reaction is first order in both cerium(IV) and manganese(II), and the order with respect to glycerol concentration varies from first to zero order as the glycerol concentration increases. Increase in sulphuric acid concentration, added sulphate and bisulphate all decrease the rate. Added cerium(III) retards the rate of reaction, whereas glycolic aldehyde had no effect. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Mn(H₂O)₄]²⁺. A mechanism is proposed, and the reaction constants and activation parameters have been determined.     

Osmium(VIII) mediated oxidation of mercury(I) by cerium(IV) in aqueous sulphuric acid – a kinetic and mechanistic study

The oxidation of Hg^I by Ce^IV has been studied in aqueous H₂SO₄. A minute amount (10^–6 mol dm^–3) of Os^VIII is sufficient to catalyse the reaction. The active catalyst, substrate and oxidant species are H₂OsO₅, [Hg₂(SO₄)HSO₄]^– and H₃Ce(SO₄)^– ₄, respectively. Possible mechanisms are proposed and the reaction constants involved have been determined.     

Kinetics of peroxodisulphate oxidation of octacyanomolybdate(IV) in concentrated aqueous salt solutions

Summary Rate constants are reported for the oxidation by peroxodisulphate ions of octacyanomolybdate(IV) in concentrated aqueous salt solutions containing up to 6 mol dm^–3 salt including mixed salt solutions. The dependence of the logarthm of rate constant on salt concentration is discussed in terms of ionic hydration enthalpies and B-viscosity coefficients. The analysis confirms that ion-pairs play a key role in determining reactivities in these systems.     

Kinetics and mechanism of benzene oxidation by peroxymonosulfate catalyzed with a binuclear manganese(IV) complex in the presence of oxalic acid

It is established that Oxone (peroxymonosulfate, 2KHSO₅ · KHSO₄ · K₂SO₄) oxidizes benzene to p-quinone very efficiently and selectively in a homogeneous solution in aqueous acetonitrile in the presence of a catalyst, i.e., dimeric manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ where L is 1,4,7-trimethyl-1,4,7-triazacyclononane, and a cocatalyst, i.e., oxalic acid. The dependences of the maximum rate of quinone accumulation on the initial concentrations of reagents are studied. It is proposed that benzene is oxidized by the manganyl particle containing the Mn(V)=O fragment that forms upon the reaction of the reduced form of the starting dimeric manganese complex with Oxone.     

Ruthenium(III)‐mediated oxidation of D‐mannitol by cerium(IV) in aqueous sulfuric acid medium: A kinetic and mechanistic approach

The oxidation of D ‐mannitol by cerium(IV) has been studied spectrophotometrically in aqueous sulfuric acid medium at 25°C at constant ionic strength of 1.60 mol dm^?3. A microamount of ruthenium(III) (10^?6 mol dm^?3) is sufficient to enhance the slow reaction between D ‐mannitol and cerium(IV). The oxidation products were identified by spot test, IR and GC‐MS spectra. The stoichiometry is 1:4, i.e., [D ‐mannitol]: [Ce(IV)] = 1:4. The reaction is first order in both cerium(IV) and ruthenium(III) concentrations. The order with respect to D ‐mannitol concentration varies from first order to zero order as the D ‐mannitol concentration increases. Increase in the sulfuric acid concentration decreases the reaction rate. The added sulfate and bisulfate decreases the rate of reaction. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Ru(H₂O)₆]³⁺, respectively. A possible mechanism is proposed. The activation parameters are determined with respect to a slow step and reaction constants involved have been determined. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 440–452, 2010     

Kinetics of alkane oxidation by chromic acid in aqueous solutions of Ir(IV) chloride complexes

The kinetics of propane and isobutane oxidation by aqueous solutions of chromic acid in the presence of Ir(IV) chloride complexes has been studied. Reaction rate decreases with increasing Cl ion concentration and decreasing acidity. Ir(H₂O)Cl ₅ ^– complexes are by an order of magnitude more active than IrCl ₆ ^2– .

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Ir(IV). Cl- . Ir(H₂O)Cl ₅ ^– , IrCl ₆ ^2– .

     

Removal of uranium from aqueous solutions by diatomite (Kieselguhr)

In this study, the removal of uranium from aqueous solutions by diatomite earth (Kieselguhr) fine particules has been investigated. Diatomite earth is an important adsorbent material in chromatographic studies. Uranium adsorption capacity of four different types of diatomite was determined. The adsorption of uranium on the chosen diatomite sample was examined as a function of uranium concentration, solution pH, contact time and temperature. The adsorption of uranium on diatomite followed a Langmuir-type isotherm.     

Reaction between cis-diaquabisbiguanideruthenium(III) and hexathiocyanatochromium(III) ions in aqueous media. A mechanistic survey on the formation of a dinuclear bridged complex

The reaction between two complex species [Ru(BigH)₂(H₂O)₂]³⁺ and [Cr(SCN)₆]^3– has been investigated in aqueous medium in the pH range 4.00–6.10, and followed in the 21–40 °C range. Pseudo-first order rate constants were evaluated using the chromium complex in a ten-fold excess. The plot of k _obs versus pH has a bell shaped profile. From this and other evidence it was concluded that only the [Ru(BigH)₂(OH)(H₂O)]²⁺ form of the ruthenium complex is reactive under the experimental conditions, and forms the dinuclear complex [Ru(BigH)₂--(SCN)₂-Cr(NCS)₄]⁰. The rate constant for the dinuclear complex formation at 31 °C is (2.57 ± 0.05) × 10^–3 mol^–1 s^–1. H = 60 ± 2 kJ mol^–1 and S = 116 ± 10 J K^–1 mol^–1.     

Kinetics and mechanisms of the oxidation of iodide and bromide in aqueous solutions by a trans-dioxoruthenium(VI) complex

The kinetics and mechanisms of the oxidation of I (-) and Br (-) by trans-[Ru (VI)(N 2O 2)(O) 2] (2+) have been investigated in aqueous solutions. The reactions have the following stoichiometry: trans-[Ru (VI)(N 2O 2)(O) 2] (2+) + 3X (-) + 2H (+) --> trans-[Ru (IV)(N 2O 2)(O)(OH 2)] (2+) + X 3 (-) (X = Br, I). In the oxidation of I (-) the I 3 (-)is produced in two distinct phases. The first phase produces 45% of I 3 (-) with the rate law d[I 3 (-)]/dt = ( k a + k b[H (+)])[Ru (VI)][I (-)]. The remaining I 3 (-) is produced in the second phase which is much slower, and it follows first-order kinetics but the rate constant is independent of [I (-)], [H (+)], and ionic strength. In the proposed mechanism the first phase involves formation of a charge-transfer complex between Ru (VI) and I (-), which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [Ru (IV)(N 2O 2)(O)(OHI)] (2+), and a one electron transfer to give [Ru (V)(N 2O 2)(O)(OH)] (2+) and I (*). [Ru (V)(N 2O 2)(O)(OH)] (2+) is a stronger oxidant than [Ru (VI)(N 2O 2)(O) 2] (2+) and will rapidly oxidize another I (-) to I (*). In the second phase the [Ru (IV)(N 2O 2)(O)(OHI)] (2+) undergoes rate-limiting aquation to produce HOI which reacts rapidly with I (-) to produce I 2. In the oxidation of Br (-) the rate law is -d[Ru (VI)]/d t = {( k a2 + k b2[H (+)]) + ( k a3 + k b3[H (+)]) [Br (-)]}[Ru (VI)][Br (-)]. At 298.0 K and I = 0.1 M, k a2 = (2.03 +/- 0.03) x 10 (-2) M (-1) s (-1), k b2 = (1.50 +/- 0.07) x 10 (-1) M (-2) s (-1), k a3 = (7.22 +/- 2.19) x 10 (-1) M (-2) s (-1) and k b3 = (4.85 +/- 0.04) x 10 (2) M (-3) s (-1). The proposed mechanism involves initial oxygen atom transfer from trans-[Ru (VI)(N 2O 2)(O) 2] (2+) to Br (-) to give trans-[Ru (IV)(N 2O 2)(O)(OBr)] (+), which then undergoes parallel aquation and oxidation of Br (-), and both reactions are acid-catalyzed.