Efficient solvent-free iron (III) catalyzed oxidation of alcohols by hydrogen peroxide

Selective oxidation of secondary and benzylic alcohols was efficiently accomplished by H₂O₂ under solvent-free condition catalyzed by FeBr₃. Secondary alcohols are selectively oxidized even in the presence of primary ones. This method is high yielding, safe and operationally simple.     

Kinetics of oxidation of o-dianisidine by hydrogen peroxide in the presence of antibody complexes of iron(III) coproporphyrin

The complex of iron(III) coproporphyrinl (FeCPI) with antibody D5E3 was studied as an artificial peroxidase, usingo-dianisidine as a substrate. At saturation with respect to antibody, the initial rates ofo-dianisidine oxidation are practically the same for free and bound FeCPI at a concentration 5 × 10^-9M, but the catalytic rate constant (k_c) for bound FeCPI exceed (k_c) for free FeCPI by two-to threefold. This difference can be explained by a real enhancement of (k_c) at the antibody-active site. The dependence of initial rates of the reaction on substrate concentrations obeyed Michaelis-Menten kinetics and revealed substrate activation at high concentrations ofo-dianisidine. A comparison of the Stern-Volmer constants foro-dianisidineinduced quenching of the porphyrin fluorescence proves that antibody-bound coproporphyrin is equivalently accessible to the substrate as protoporphyrin bound to apoperoxidase from horseradish peroxidase (HRP). Based on analysis of the (k_c) dependence on H₂O₂ concentrations in the FeCPI-antibody system, we suggest that interaction with hydrogen peroxide is the rate-limiting step for the oxidation reaction.     

Determination of hydrogen peroxide by thallium(III) in the presence of iron(II)

A method for estimating hydrogen peroxide by oxidation with excess of thallium(III) in the presence of iron(II) and iodometric determination of excess of thallium(III) is described. Nitrate, sulphate, manganese(II) and copper(II) have no effect. Chloride interferes.     

Trace metal-ion catalysis: kinetics and mechanism of oxidation of l-ascorbic acid by chromium(VI) in phosphate buffers

Summary The kinetics of oxidation of l-ascorbic acid (H₂A) by Cr^VI with and without added Cu^II conforms to the stoichiometry represented by the equation: 2Cr^VI + 3H₂A 2Cr^III + 3A + 6H⁺ where A is dehydroascorbic acid. The mode of the electron transfer from H₂A to Cr^VI is suggested to involve oxidative decomposition of an intermediate complex. Catalysis by Cu^II is indicated via complexation of the catalyst and substrate. The inhibitory effects of Cl^–, NO _f3 ^p– and SO _f4 ^p2– ions indirectly support complexation between Cr^VI and H₂A.     

Molybdenum(VI) catalysis of perborate or hydrogen peroxide oxidation of iodide ion

Summary Perborate in aqueous solution generates H₂O₂; in its presence the molybdenum(VI) catalysed oxidation of iodide ion is first order with respect to the oxidant and catalyst, and is independent of [I^–] and [H⁺]. Kinetic studies point to peroxymolybdenum(VI) species as the oxidizing species.     

Study on kinetics and mechanism of copper-catalyzed oxidation of hydrazine by iron (III) in acid solution

The copper-catalyzed oxidation of hydrazine by iron(III) in acid solution follows the rate law -d[Fe(III)]/dt = kK_h[Cu(II)]²/(K_h + [H⁺]), where K_h is the hydrolysis constant of Cu²⁺, k was found to be 8.8±0.8, 13.2±1.4 and 17.5±1.3 min^?1 at 35, 40, and 45°C respectively and μ= 0.2 mol/L. The composition of the activated complex is Cu²⁺, CuOH⁺, N₂H₄, H⁺ or others. Perhaps several hydrazine complexes of Cu(II) participate in the reaction and one of them isolated was Cu(N₂H₄)₂(HSO₄)₂. Study on the oxidation of this complex is also in conformity with the above rate law.     

The kinetics of iodide oxidation by hydrogen peroxide in acid solution

The kinetics of the complex reaction between I⁻ and H₂O₂ in acid media was investigated. The particular attention was focused on the determination of the rate constant of the reaction between HIO and H₂O₂ involved in the investigated complex process. The examination of the whole kinetics was performed by simultaneously monitoring the evolution of O₂ pressure, I₃⁻ and I⁻ concentrations. We modeled the behavior of experimentally followed components based on Liebhafsky’s research. Our preliminary results suggest a significantly higher rate constant (3.5 × 10⁷ M⁻¹ s⁻¹) of the reaction between HIO and H₂O₂ as those proposed in the literature.     

Kinetics and mechanism for the aquation of bismalonatoethylenediaminecobaltate(III) ion in acid perchlorate media

Summary The title complex aquates in acid media, first to [Co(mal)-(H₂O)₂(en)]⁺ (1) (Step 1) and subsequently to [Co(H₂O)₄(en)]³⁺ (2) (Step 2). Complex species (1) has been separated and characterised in solution. While Step 1 involves only a second-order acid catalysed path, Step 2 involves both a first-order acid independent path and a second-order acid catalysed path. The rate constants and activation parameters evaluated for these reaction paths have been compared with those for similar carboxylato-cobalt(III) complexes. This, together with an observed isokinetic relation, indicates that the rate-determining step involves opening of the unprotonated (in the spontaneous acid independent path) or the protonated (for the acid catalysed path) chelate ring of the malonate ligand and insignificant solvation of the central metal ion.     

Ru(III)-EDTA catalyzed oxidation of ascorbic acid by hydrogen peroxide in aqueous solution

The kinetics of oxidation of ascorbic acid to dehydroascorbic acid by hydrogen peroxide catalyzed by ethylenediaminetetraacetatoruthenate(III) has been studied over the pH range 1.50 – 2.50, at 30°C and μ = 0.1 M KNO₃. The reaction has a first-order dependence on ascorbic acid and Ru(III)-EDTA concentrations, an inverse first-order dependence on hydrogen ion concentration, and is independent of hydrogen peroxide concentration in the pH range studied. A mechanism has been proposed in which ascorbate anion forms a kinetic intermediate with the catalyst in a pre-equilibrium step. Ruthenium(III) is reduced to ruthenium(II) in a rate-determining step and is reoxidized with hydrogen peroxide back to the Ru(III) complex in a fast step.     

Kinetics and mechanism of decomposition of hydrogen peroxide in the presence of manganese(III) porphyrins

The kinetics of homogeneous decomposition of hydrogen peroxide in the presence of manganese complexes with anionic ligands and various aromatic macrocycles were studied by the volumetric method. Ionmolecular mechanism was proposed on the basis of spectrophotometric data for catalytic decomposition of hydrogen peroxide with participation of manganese(III) porphyrins. The catalytic activity of the porphyrin complexes was higher by a factor of 1.5–3 than the activity of the corresponding solvate complexes with anionic ligands. The catalytic activity of porphyrin manganese complexes can be controlled by variation of the electronic structure of the macroring and the nature of anionic ligand coordinated at the apical position.     

Kinetics and mechanism of oxidation of manganese(III) acidoporphyrin complexes with hydrogen peroxide

The reactions of manganese(III) acidotetraphenylporphyrin complexes with hydrogen peroxide in an aqueous-organic medium at 288–308 K are studied by spectrophotometry. The reaction is the oxidation of the manganese(III) complex. The spectral and kinetic data correspond to a multistep mechanism including the step of coordination of a hydrogen peroxide molecule by the central manganese atom. A possibility of formation of oxidized complexes without macrocycle destruction upon the reaction with H₂O₂ makes manganese(III) porphyrins quite promising for use as models of natural catalases.     

Kinetics and mechanism of the oxidation of hydrogen peroxide by the octacyanotungstate(V) ion in alkaline aqueous media

Summary The oxidation of H₂O₂ by [W(CN)₈]^3– has been studied in aqueous media between pH 7.87 and 12.10 using both conventional and stopped-flow spectrophotometry. The reaction proceeds without generation of free radicals. The experimental overall rate law, , strongly suggests two types of mechanisms. The first pathway, characterized by the pH-dependent rate constant k _s, given by , involves the formation of [W(CN)₈· H₂O₂]^3–, [W(CN)₈· H₂O₂·W(CN)₈]^6– and [W(CN)₈· HO]^3– intermediates in rapid pre-equilibria steps, and is followed by a one-electron transfer step involving [W(CN)₈·HO]^3– (k _a) and its conjugate base [W(CN)₈·O]^4– (k _b). At 25 °C, I = 0.20 m (NaCl), the rate constant with H _a =40±6kJmol^–1 and S _a =–151±22JK^–1mol^–1; the rate constant with H _b =36±1kJmol^–1 and S _b =–136±2JK^–1mol^–1 at 25 °C, I = 0.20 m (NaCl); the acid dissociation constant of [W(CN)₈·HO]^3–, K ₅ =(5.9±1.7)×10^–10 m, with and is the first acid dissociation constant of H₂O₂. The second pathway, with rate constant, k _f, involves the formation of [W(CN)₈· HO₂]^4– and is followed by a formal two-electron redox process with [W(CN)₈]^3–. The pH-dependent rate constant, k _f, is given by . The rate constant k ₇ =23±6m ^–1 s ^–1 with and at 25°C, I = 0.20 m (NaCl).     

Kinetics and mechanism of the oxidation of formic acid by thallium(III). Reinvestigation of hydrogen ion dependence

The rate of the oxidation of formic acid by thallium(III) in (Li, H)ClO₄ solutions is not affected by variation in hydrogen ion concentration and the experimental rate law, $$\frac{{ - d\left[ {T\left( {III} \right)} \right]}}{{d t}} = \frac{{k_1 K\left[ {T\left( {III} \right)} \right]\left[ {HCOOCH} \right]}}{{1 + K\left[ {HCOOH} \right]}}$$ is consistent with the mechanism which requires the formation of intermediate complex [HCOOHTl]³⁺ in a rapid preequilibrium followed by its slow decomposition to yield the final products. At 75°,k ₁ andK have the values of 16±1×10^?5 sec^?1 and 7.3±0.5M ^?1 resp.     

Kinetics and mechanism of reduction of thallium(III) by hydrogen peroxide in perchloric acid medium

The kinetics and mechanism of reduction of thallium(III) by hydrogen peroxide has been studied in 1.0 mol dm^–3 perchloric acid medium. The reaction is first order with respect to thallium(III) and second order with respect to hydrogen peroxide. A negative hydrogen ion and chloride ion catalysis is observed. Bromide ion is found to catalyze the reaction in low concentration. There is no effect of ionic strength on the rate of the reaction. A plausible mechanistic pathway for the reaction is suggested which leads to the following rate law: Rate=–d[T1(III)]/dt=kK[T1(III)][H₂O₂]²/[H⁺] where K is the formation constant of the complex between thallium(III) and hydrogen peroxide and k is the rate constant of the reaction between that complex and hydrogen peroxide. The computed values of E_a and S^# are 44.8±6.5 kJ mol^–1 and –107.8±22.2 JK^–1 mol^–1, respectively.

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(III) - - . - (III) . - - . . -- . , - :=–[T1(III)]/dt=kK[T1(III)][H₂O₂]²/[H⁺], - (III) - . E_A S^# 44,8±6,5 / –107,8±22,1 /·, .

     

Kinetics and mechanism of oxidation of quinols by tris(1,10-phenanthroline) iron(III) complexes in aqueous acidic perchlorate media

The kinetics of oxidation of several substituted quinols by a series of Tris(1,10-phenanthroline)iron(III) complexes has been investigated with a stopped-flow technique at 6.0 and 20.0°C. The reactions were found to be first order on both reactants and independent of acidity. The second-order specific rate constants were strongly dependent on free energy of reaction. An interpretation of the mechanism in the light of Marcus theory has been developed. The first electron abstraction with semiquinone radical formation has been suggested as the rate-determining step, and on this basis, intrinsic parameters of the reactions have been derived. A good agreement was found between experimental and computed data.     

Kinetics and mechanism of ruthenium(III)-catalysed oxidation of allyl alcohol by acid bromate-autocatalysis in catalysis

The kinetics of oxidation of CH₂=CHCH₂OH with KBrO₃ in the presence of Ru^III catalyst in aqueous acid medium has been studied under varying conditions. The active species of oxidant and catalyst were HBrO₃ and [Ru(H₂O)₆]³⁺ respectively. The autocatalysis exhibited by one of the products, i.e., Br^–, was attributed to the formation of a complex between the bromide ion and Ru^III. A composite scheme and rate law were proposed. Reaction constants involved in the mechanism have been evaluated.     

The decomposition kinetics of hydrogen peroxide catalyzed by diethylenetriaminepentaacetatoiron(III) complex

The rate of reaction of (Fe(DTPA)) with H₂O₂ was investigated at various temperatures. The observed rate law is given by the expression. The rate constants and the related thermodynamic parameters are calculated. Substitution controlled mechanisms are suggested to account for the formation of the violet peroxy intermediate. The results are compared with previously data for Fe EDTA complex.     

Simple one‐pot conversion of organic compounds by hydrogen peroxide activated by ruthenium(III) chloride: organic conversions by hydrogen peroxide in the presence of ruthenium(III)

The aromatic compounds p‐nitrobenzaldehyde, p‐hydroxybenzaldehyde, naphthalene, toluene, catechol, quinol, aniline and toluidine dissolved in aqueous acetic acid or aqueous medium were oxidized in quantitative to good yields by 50% H₂O₂ in the presence of traces of RuCl₃ (～10^?8 mol; substrate/catalyst ratio 1488:1 to 341 250:1). Conditions for highest yields, in the most economical way, were obtained. Higher catalyst concentrations decrease the yield. Oxidation in aromatic aldehydes is selective at the aldehydic group only. In the case of hydrocarbons, oxidation results in the introduction of a hydroxyl group with >85% (in the case of toluene) selectivity for the ortho position. Formation of low‐molecular‐weight polyaniline was reduced to 10%, along with 90% formation of higher molecular weight polyaniline. In this new, simple and economical method, which is environmentally safe and requires less time, oxo‐centered carboxylate species of ruthenium(III) in acetic acid medium and hydrated ruthenium(III) chloride in aqueous medium probably catalyze the oxidation. Copyright © 2005 John Wiley & Sons, Ltd.     

Kinetics and mechanism of the oxidation of hydrazinium ion by gold(III) in hydrochloric acid medium

Summary Kinetics of the oxidation of hydrazinium ion by gold(III) have been studied spectrophotometrically in hydrochloric acid medium. The reaction is first-order with respect to both gold(III) and hydrazinium ion. Hydrogen ion inhibits the oxidation. The mechanism of the reaction is discussed.