Kinetics and mechanism of ruthenium(III) catalyzed oxidation of tellurium(IV) by cerium(IV)

The reaction is zero order in cerium(IV), fractional order in tellurium(IV) and first oder in ruthenium(III). While the ionic strength has no effect, the rate increases with increasing [H⁺], and decreases with increasing [HSO ₄ ^– ]. H and S are 54.4 kJ mol^–1 and –60.3 JK^–1 mol^–1, respectively. A suitable mechanism is proposed.

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(IV), (IV) (III). , [H⁺] [HSO ₄ ^– ]. H S 54,4 ^–1 –60,3 ·^–1·^–1, . .

     

Kinetics and mechanism of oxidation of hypophosphite by Waugh-type enneamolybdomanganate(IV) in perchloric acid

The reaction between hypophosphite and enneamolybdomanganate(IV) in perchloric acid was carried out under pseudo-first-order conditions keeping large excess of hypophosphite. The order in oxidant was found to be unity and that of hypophosphite was found to be less than unity. The reaction proceeds with prior formation of complex between the reactants followed by its rate determining decomposition. The accelerating effect of hydrogen ions on the reaction is due to the formation of active hexaprotonated oxidant species. The formation of the complex is supported by kinetic results and also by spectrophotometric study. The product of the reaction was found to be phosphitomolybdate, [H₁₀(HP)Mo₆O₂₆]²⁻, which was confirmed by FTIR study and AAS analysis. The reaction involves direct two-electron transfer step without any free radical intervention. The effect of ionic strength, solvent polarity and the activation parameters were also in support of the mechanism proposed.     

Kinetics and mechanism of oxidation of D-altrose by aqua-cerium(IV) in perchloric acid medium

Kinetics of the oxidation of D-altrose by Ce(IV) perchlorate has been studied in perchloric acid medium. At equivalent concentrations the overall order of the reaction is two, being unity in each reactant. The reaction is characterized by a primary positive kinetic salt effect. Perchloric acid has been found to enhance the rate, while the addition of the reaction products retards the rate. No evidence for initial complexation has been obtained. Thermodynamic parameters have been determined and a mechanism consistent with the observed results is proposed.

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D- Ce(IV) . , . . , . . , .

     

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

The kinetics of Ru^III-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 Ru^III and Te^IV, 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.     

Mechanism of oxidation of selenium(IV) by cobalt(III) in perchloric acid — a kinetic study

Summary The kinetics of Co^III oxidation of Se^IV have been studied in aqueous HClO₄. The order with respect to Co^m is two the order with respect to Se^IV is one at low concentrations; two at high concentrations. The latter variation is attributed to the greater reactivity of the Se^IV dimier A mechanism involving complexation between oxidant and substrate is proposed. [CoOH]²⁺ is presumed to be the reactive Co^III species and H₂SeO₃ and HSeO ₃ ^– to be those of Se^IV. At 25° C, E_a, H and S for the monomeric path are 125.6±4.0 kJ mol^–1, 122.1±3.8 kJ mol^–1 and 206±12 JK^–1 mol^–1 respectively and those for the dimeric path are 88.6±3.6 kJ mol^–1, 85.9±3.4 kJ mol^–1 and 62.6±11.3 JK^–1 mol^–1 respectively.     

Kinetics and mechanism of the oxidation of 2-furancarbox-aldehyde by thallium(III) in perchloric acid solutions

The kinetics of the oxidation of 2-furancarboxaldehyde by thallic perchlorate at 50°C obeys the rate law

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aminoalcohols by chloramine-T in perchloric acid

Summary The kinetics of the ruthenium(III) catalysed oxidation of 2-aminoethanol, 3-aminopropanol, diethanolamine and triethanolamine by chloramine-T in HClO₄ medium have been studied. The reactions exhibits first order rate dependence with respect to the oxidant and to the catalyst, and are zeroth order with respect to the substrate. The rate of oxidation is proportional to k[HClO₄]/{k+k'[HClO₄]} where k, k and k' are constants (a mixture of elementary rate constants and equilibrium constants). A suitable mechanism consistent with the observed kinetic data is proposed.     

Kinetics and mechanism of osmium(VIII) catalyzed oxidation of tellurium(IV) by cerium(IV)

The reaction is first order in substrate and catalyst and zero order in cerium(IV). The rate decreases with increasing [H⁺] as well as with increasing ionic strength. H and S have been found to be 44.8 kJ mol^–1 and 161.8 JK^–1 mol^–1 respectively. A mechanism is proposed.

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(IV). [H⁺], . , H S 44,8 ·^–1 161,8 ·^–1–1, . .

     

Determination of tellurium(IV) in perchloric acid by stripping voltammetry with collection

The deposition and stripping of teUurium(IV) at a rotating gold ring—gold disk electrode is described. Tellurium(IV) is reduced to the metal by two cathodic procedures, and three activity states of electrodeposited tellurium are observed. For sub-monolayer depositions, a single stripping peak is observed. Determination of telIurium(IV) by stripping voltametry and by Stripping voltammetry with collection is described. The detection limits are 1 X 10^-5 M and 5 X 10^-11 M, respectively.     

Kinetics and mechanism of sulphurous acid oxidation by hexachloroiridate(IV) in hydrochloric acid

Summary The reaction between sulphurous acid and hexachloroiridate(IV) appears to take place through the formation of an intermediate complex followed by decomposition to give oxidation products. The rate is retarded as the hydrogen ion concentration increases. Thermodynamic parameters associated with the equilibrium step as well as with the slowest step have been calculated. The probable mechanism of the reaction is discussed.     

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 the oxidation of acetaldehyde by chromic acid in perchloric acid

Summary The oxidation of MeCHO by chromium(VI) has been studied in HClO₄ medium over a wide range of experimental conditions and has been found to obey the rate law;v=k[MeCHO][HCrO ₄ ^– ][H⁺]. The calculated H and-S values for the reaction are 30±2kJ mol^–1 and 171±7J mol^–1deg^–1, respectively. The mechanism is discussed in terms of carbon-hydrogen bond cleavage.     

Kinetics of cerium(IV) oxidation of propionic acid in perchloric acid: Role of solvent

The oxidation rate of propionic acid (PROA) by cerium(IV) in aqueous perchloric acid (1.0–6.0 mol/dm³) is proportional to the PROA concentration, the total order of the reaction being two. It was found that the rate is related to the values of Hammett's acidity function (H₀) in agreement with both Zucker-Hammett's hypothesis and Bunnett-Olsen's criterion, the water acting as a proton transfer agent. A mechanism consistent with the findings is proposed.

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() (IV) (1,0–6,0 /³) . (H₀) -, -. . .

     

Kinetics and mechanism of osmium (VIII) and ruthenium(III) catalyzed oxidation of aliphatic amines by chloramine-T in alkaline and perchloric acid media

The kinetics of oxidation of aliphatic amines viz., ethylamine, n-butylamine, isopropylamine (primary amines), diethylamine (secondary amine), and triethylamine (tertiary amine) by chloramine-T have been studied in NaOH medium catalyzed by osmium (VIII) and in perchloric acid medium with ruthenium(III) as catalyst. The order of reaction in [Chloramine-T] is always found to be unity. A zero order dependence of rate with respect to each [OH^?] and [Amine] has been observed during the osmium(VIII) catalyzed oxidation of diethylamine and triethylamine while a retarding effect of [OH^?] or [Amine] on the rate of oxidation is observed in case of osmium(VIII) catalyzed oxidation of primary aliphatic amines. The ruthenium(III) catalyzed oxidation of amines follow almost similar kinetics. The order of reactions in [Amine] or [Acid] decreases from unity at higher amine or acid concentrations. The rate of oxidation is proportional to {k′ and k″ [Ruthenium(III)] or [Osmium(VIII)]} where k′ and k″ (having different values in case of ruthenium(III) and osmium(VIII)) are the rate constants for uncatalyzed and catalyzed path respectively. The suitable mechanism consisting with the kinetic data is proposed in each case and discussed.     

Kinetics and mechanism of ruthenium (III) catalyzed oxidation of ethanol by cerium (IV) in aqueous sulfuric acid media

The kinetics of oxidation of ethanol by cerium(IV) in presence of ruthenium(III) (in the order of 10^?7 mol dm^?3) in aqueous sulfuric acid media have been followed at different temperatures (25–40°C). The rate of disappearance of cerium(IV) in the title reaction increases sharply with increasing [C₂H₅OH] to a value independent of [C₂H₅OH] over a large range (0.2–1.0 mol dm^?3) in which the rate law conforms to: where [Ru]_T gives the total ruthenium (III) concentration. The values of 10^?3k_c and 10^?3k_d are 3.6 ± 0.1 dm³ mol^?1 s^?1 and 3.9 ± 0.2 s^?1, respectively, at 40°C, I = 3.0 mol dm^?3. The proposed mechanism involves the formation of ruthenium(III)^? substrate complex which undergoes oxidation at the rate determining step by cerium(IV) to form ruthenium(IV)^? substrate complex followed by the rapid red-ox decomposition giving rise to the catalyst and ethoxide radical which is oxidized by cerium(IV) rapidly. The mechanism is consistent with the existence of the complexes Ru^III · (C₂H₅OH) and Ru^III · (C₂H₅O^?) and both are kinetically active. The overall bisulphate dependence conforms to: k_obsd = A[Ru]_T/{1 + C[HSO₄^?]} where A = 2.2 × 10⁴ dm³ mol^?1 s^?1, C = 1.3 at 40°C, [H⁺] = 0.5 mol dm^?3, and I = 3.0 mol dm^?3. The observations are consistent with the Ce(SO₄)₂ as the kinetically active species. © 1995 John Wiley & Sons, Inc.     

Kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol by cerium(IV) in sulfuric acid media

The kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol (THFA) by cerium(IV) in sulfuric acid media have been investigated spectrophotometrically in the temperature range 298–313 K. It is found that the reaction is first-order with respect to Ce^IV, and exhibits a positive fractional order with respect to THFA and Ru^III. The pseudo first-order ([THFA]≫[Ce^IV]≫[Ru^III]) rate constant k _obs decreases with the increase of [HSO ₄ ⁻ ]. Under the protection of nitrogen, the reaction system can initiate polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a reasonable mechanism has been proposed and the rate equations derived from the mechanism can explain all the experimental results. From the dependence of k _obs on the concentration of HSO ₄ ⁻ , has been found as the kinetically active species. Furthermore, the rate constants of the rate determining step together with the activation parameters were evaluated.     

Kinetics and mechanism of palladium(II) catalysed oxidation of amines and aminoalcohols by N-bromosuccinimide in perchloric acid

Summary The kinetics of oxidation of amines (EtNH₂, Et₂NH, Et₃N) and aminoalcohols [H₂NCH₂CH₂OH, H₂N(CH₂)₃OH, (CH₂CH₂OH)₂NH, (CH₂CH₂OH)₃N] by N-bromosuccinimide (NBS) have been studied in aqueous HClO₄ with PdCl₂ as catalyst, and in the presence of Hg(OAc)₂ to ensure oxidation by pure NBS. The order of reaction with respect to NBS was unity, however, an increase in [NBS]₀ resulted in a decrease in the rate constant. The rate was directly proportional to [Pd^II] for the aminoalcohols while for EtNH₂ the rate was proportional to k + k[Pd^II] (where k and k are rate constants for the uncatalysed and catalysed paths, respectively). Retarding effects for HClO₄, succinimide, Cl^– and AcOH on the rate of oxidation were observed. The kinetic data support the formation of [Pd^II-A] and [Pd^II-(A)₂] complexes (where A represents amine or aminoalcohol). A mechanism, consistent with the observed kinetic data, is proposed.     

Kinetics and mechanism of oxidation of L-ascorbic acid by platinum(IV) in aqueous acid medium

The oxidation of l-ascorbic acid (H₂A) by platinum(IV) in aqueous acid medium exhibits overall second-order kinetics, being first order with respect to each reactant. Increasing both hydrogen and chloride ion concentrations inhibits the rate. The stoichiometry involves reaction of one platinum(IV) ion with H₂A to give dehydroascorbic acid. A reaction mechanism consistent with all the experimental observations is proposed.