Kinetics and mechanism of the inner-sphere reduction of hexachloroplatinate(IV) by dithionite in acetate buffer

The kinetics of reduction of hexachloroplatinate(IV) by dithionite have been examined spectrophotometrically in sodium acetate?Cacetic acid buffer medium in the temperature range 288?C303?K. The reaction is first order in both platinum(IV) species and dithionite. H⁺ ion has an inhibiting effect on the rate in the pH range 3.68?C4.80. The pseudo-first order rate constant increased upon increasing both ionic strength and dielectric constant. The suggested mechanism involves an initial transition state between two like charged ions, which then decomposes to give SO₃ ^2? through the intermediate formation of free radicals. The presence of free radicals was confirmed by performing the reaction in the presence of acrylamide. PtCl₆ ^2? is finally reduced to PtCl₄ ^2?, as confirmed by thermogravimetric analysis and IR spectrophotometry. The values of ?H^?? and ?S^?? associated with the rate-determining step have been calculated as 33?±?4?kJ?mol^?1 and ?141?±?7?JK?mol^?1, respectively. The values of ?H° and ?S° for the dissociation of HS₂O₄ ^? are 16?±?4?kJ?mol^?1 and ?14?±?7?JK?mol^?1, respectively.     

Kinetics and mechanism of the oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)iron(II) bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III) in acetate buffer

The rapid oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)-iron(II), [Fe(TPTZ)₂]²⁺, bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III), [Mn^III(Y)]⁻, in acetate buffers was monitored using stopped-flow spectrophotometry. The reaction is first order in the substrate and evidence was obtained for pre-complexation between the oxidant and the substrate. The reaction rate increases as the pH increases. Characterisation of the products using the radiotracers⁵⁴Mn and⁵⁹Fe indicated that [Mn^II(Y)]²⁻ and [Fe(TPTZ)₂]³⁺ are the final products. The reaction obeys the rate law:

Kinetics and mechanism of oxidation of uric acid by hexacyanoferrate(III) in acetate buffers

The second order kinetics of uric acid oxidation by hexacyanoferrate(III) in acetate buffers were studied by estimating oxidant colorimetrically at 420 nm. Two moles of organic acid react with one mole of the oxidant and oxidation products are alloxan and urea. TMC 2661     

Kinetics and mechanism of the reduction of tetrachloroaurate(III) by formate in acidic aqueous solution

Rate data for the reduction of AuCl₄⁻ by formate, were measured at different temperatures, formate, hydrogen and chloride ion concentrations. AuCl₄⁻ and AuCl₃(OH)⁻ react with HCOOH and HCOO⁻ in the rate-determining steps of the suggested reaction mechanism to produce AuCl₃(HCOO)⁻. The latter species undergoes a rapid redox reaction in which AuCl₂⁻, Au(o) and CO₂ are produced.     

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.     

Kinetics and mechanism of formation of penta-ammineglycinecobalt(III) ion from aquopenta-amminecobalt(III) ion and glycine in acid media

The rates of formation of penta-ammineglycinecobalt(III) ion from aquopenta-amminecobalt(III) ion and glycine in acidic media have been studied spectrophotometrically at different glycine concentration and different pH in the range of 50–70°C. The ΔH≠ and ΔSz≠ values are 27.6 kcal mole^?1 and +5.2 e. u. respectively, and increase in ionic strength causes only a slight acceleration of the rate. The results are consistent with a mechanism involving outer-sphere association between the aquopenta-amminecobalt(III) complex and glycine, followed by its transformation into the product by an essentially dissociative process in which rupture of the Co(III)? OH₂ bond is primarily important in the transition state (S_N1IP mechanism).     

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aliphatic acids by peroxodiphosphate in acetate buffers

Summary The kinetics of oxidation of aliphatic acids (AAs), such as propionic acid, butyric acid, isobutyric acid and valeric acids, by peroxodiphosphate (PDP) using ruthenium(III) as catalyst in aqueous H₂SO₄ at constant ionic strength and different acidities were studied. The ruthenium(III)-catalysed oxidation is first order in [PDP] and fractional order in [AA]. The order with respect to [Ru^III] is fractional. An analysis of the rate dependence upon [H^–] suggests that H₃P₂O ₈ ^– is the active oxidizing species in the oxidation. A mechanism consistent with the rate law is proposed.     

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.     

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 of oxidation of glycine and related substrates by diperiodatoargentate (III)

The reactions of diperiodatoargentate(III) with glycine and related compounds have been examined. The monoperiodatosilver(III) species acts as an active oxidant in comparison to that of diperiodatosilver(III) species. These reactions consist of three kinetically distinguishable steps-induction period, complexation and oxidation. Complexation of these substrates takes place with a second order rate constant of (0.2–1.6)×10⁴ dm³ mol⁻¹ s⁻¹ whereas the redox process occurs at a rate of (0.3–6.0)×10² dm³ mol⁻¹ s⁻¹ except in case of cysteine with which these processes occurred by an order of magnitude faster. The rate of electron transfer from carboxylic acids to the silver(III) complex is observed to be several order of magnitude smaller in comparison to that of amino acids. Both the rate of complexation and electron transfer are influenced by the structure of the substrates. The aquated silver(III) species is found to be more reactive in comparison to the hydroxylated silver(III) species.     

Kinetics and mechanism of palladium(II) acetate reduction by hydrogen on the surface of a carbon support

The kinetics of the reduction of Pd(II) compounds by dihydrogen on the surface of a carbon support has been investigated for palladium acetate as an example. A kinetic model has been constructed for this reaction. An autocatalytic mechanism is suggested, in which the key role is played by Pd(0) compounds and their hydrides. The reaction occurring on the support surface is compared with the same reaction in solutions of palladium phosphine acetate complexes, where a similar mechanism is observed. One of the most important features of the surface reaction is the relatively slow reduction of the Pd(I) compounds to Pd(0). This makes it possible to obtain materials with a high Pd(I) content of 5% and above.     

Kinetics and mechanism of oxidation of uric acid with thallium(III) in acetate buffers

The kinetics of oxidation of uric acid by thallium(III) has been studied in acetate buffers; the oxidation products are alloxan and urea. Deprotonated uric acid, UaH⁻, and T1(OAc)₃ are the reacting species. A probable reaction mechanism has been proposed conforming with rate law (1)-d[T1^III]/dt=(k′₁K′₁+k′₂K′₂K₁/[H⁺]) [T1^III][UaH₂]/1+K₄[OAc⁻] A comparative analysis with other soft acids Hg^II and Pb^IV has been attempted.     

Kinetics of reduction of ruthenium(III) by sodium tetrahydroborate

Summary The kinetics of reduction of ruthenium(III) by sodium tetrahydroborate in aqueous acidic medium have been studied. The effect of variation in the concentration of substrate (RuCl₃·3H₂O), pH, and reductant (BH₄ ^–1) has been studied. The activation parameters were evaluated. Based on a one-electron transfer, the mechanism involves the reduction of ruthenium(III) by hydrogen.     

Kinetics and mechanism of the reduction of enneamolybdomanganate(IV) by sulfite

The kinetics and mechanism of reduction of enneamolybdomanganate(IV) by sulfite in HOAc—NaOAc buffer solution was studied by spectrophotometry. The reaction, with respect to enneamolybdomanganate(IV), is pseudo-first-order and, with respect to sulfite, is first-order. [H⁺]/k _obs increases with the concentration of H⁺ and the reaction rate increases with temperature. The rate constants and activation parameters of the rate-determining steps were evaluated. A mechanism related to the reaction is proposed.     

Kinetics and mechanism of formation of square-planar copper(II) and nickel(II) complexes of ethylenebisbiguanide in aqueous acetate buffer media

Summary The kinetics of formation of square-planar Cu^II and Ni^II complexes of the quadridentate ligand, ethylenebisbiguanide, have been studied spectrophotometrically in aqueous HOAc–NaOAc buffer, at ionic strength 0.2 mol dm^–3, in the 25–35°C temperature range. The observed rate constants for the formation reactions are independent of pH (and of OAc^– concentration) in the pH range used (3.6–4.8 for Cu^II and 5.0–5.8 for Ni^II) where the product complexes form stoichiometrically, but show first-order dependence on the ligand concentration;i.e. k_obs=k_f[L]_total. At 25°C k_f values (dm³ mol^–1s^–1) are 35.2±0.4 for Cu^II and (8.4±0.1)×10^–3 for Ni^II. The mechanism of the reactions is discussed.     

Kinetics and mechanism of the reduction of enneamolybdonickelate(IV) by iodide

The kinetics and mechanism of the reduction of enneamolybdonickelate(IV) by iodide in acid aqueous solution was studied by spectrophotometry. The reaction rate increases, as the concentration of H⁺ increases and with temperature. It shows that the reaction rate law is The reaction rate constants and activation parameters of the rate-determining steps were evaluated. A mechanism related to the reaction is proposed.     

Kinetics and mechanism of oxidation of the binary and ternary complexes of chromium(III) involving inosine and glycine by N -bromosuccinimide

The kinetics of oxidation of the chromium(III) complexes, [Cr(Ino)(H₂O)₅]³⁺ and [Cr(Ino)(Gly)(H₂O)₃]²⁺ (Ino?=?Inosine and Gly?=?Glycine) involving a ligands of biological significance by N-bromosuccinimide (NBS) in aqueous solution to chromium(VI) have been studied spectrophotometrically over the 25–45°C range. The reaction is first order with respect to both [NBS] and [Cr], and increases with pH over the 6.64–7.73 range in both cases. The experimental rate law is consistent with a mechanism in which the hydroxy complexes [Cr(Ino)(H₂O)₄(OH)]²⁺ and [Cr(Ino)(Gly)(H₂O)₂(OH)]⁺ are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant, k ₁, for the oxidation of the [Cr(Ino)(H₂O)₅]³⁺ (6.90?×?10^?4?s^?1) is lower than the value of k ₂ (9.66?×?10^?2?s^?1) for the oxidation of [Cr(Ino)(Gly)(H₂O)₂]²⁺ at 35°C and I?=?0.2?mol?dm^?3. The activation parameters have been calculated. Electron transfer apparently takes place via an inner-sphere mechanism.     

Kinetics and mechanism of the oxidation of glycolaldehyde by tetrachloroaurate(III)

The kinetics of the reaction between glycolaldehyde (GA) and tetrachloroaurate(III) in acetic acid-sodium acetate buffer has been studied. The reaction is first-order with respect to [Au^III] as well as [GA]. Both H⁺ and Cl⁻ ions retard the rate of reaction. AuCl₄⁻, AuCl₃(OH₂), and AuCl₃(OH)⁻ are the reactive species of gold(III) with gradually increasing reactivity. A reaction mechanism involving two-electron transfer rate determining steps has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 613–619, 1998