Kinetics of Hydrolysis of Diperiodatoargentate(III) Ion and its Reduction by Paracetamol

The kinetics of hydrolysis and reduction of the diperiodatoargentate(III) ion (DPA) has been studied in aqueous acidic medium spectrophotometrically. Upon dilution the silver (III) complex was found to be unstable in the presence of H₂O. Addition of [H⁺], largely increased the hydrolysis rate, whereas [OH⁻] does not have any effect. Under pseudo-first-order conditions ([paracetamol] > [DPA]), the reduction rate was very fast. Second-order conditions were used to determine the reaction rate. The reaction was acid-catalyzed and the rate decreased by the addition of periodate. The Arrhenius equation was valid for the reaction. The changes observed in the direction of the rate constant-[H⁺] profile correspond to aquation of the diperiodatoargentatate(III) complex. The proposed mechanism and the derived rate law are consistent with the observed kinetics.     

Oxidation of diclofenac sodium by diperiodatoargantate(III) in aqueous alkaline medium and its determination in urine and blood by kinetic methods

The kinetics and oxidation of diclofenac sodium (DFS) by diperiodatoargentate(III) (DPA) in alkaline medium at 298 K and at a constant ionic strength of 0.60 mol dm^?3 were studied spectrophotometrically. The oxidation products were [2‐(2,6‐dicloro‐phynylamino)‐phenyl]‐methenol and Ag(I), identified by LC‐ESI‐MS and IR spectral studies. The reaction between DFS and DPA in alkaline medium exhibits 1:1 stoichiometry. The reaction is first order in [DPA] and has a less than unit order dependence each in [DFS] and [alkali]. Increasing concentrations of IO^?₄ retard the reaction. The active species of DPA proposed to be monoperiodatoargentate(III), and a mechanism is suggested. The rate constants involved in the different steps of the mechanism were determined and are discussed. The activation parameters with respect to a rate‐limiting step of the mechanism were determined. The thermodynamic quantities were also determined. Using the oxidation of DFS by DPA, DFS was analyzed by kinetic methods in urine and blood sample. The proposed method enables DFS analysis in the range from 5.0 × 10^?5 to 5.0 × 10^?3 mol dm^?3. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 336–346, 2010     

Kinetics and mechanism of osmium(VIII)-catalyzed oxidation of phosphite by diperiodatoargentate(III) in alkaline medium

Summary The kinetics of the Os^VIII-catalyzed oxidation of phosphite by diperiodatoargentate(III) (DPA) have been investigated in aqueous base. The reaction rate is independent of [DPA], but first order with respect to [phosphite] and to [Os^VIII]. The rate of reaction increases with increase in [KOH] and tends to a limiting value. Activation parameters have been calculated and suitable mechanism is proposed to explain the observed results.     

Kinetics and mechanism of oxidation of some reducing sugars by diperiodatoargentate(III) in alkaline medium

Summary The kinetics of oxidation of d-glucose, d-galactose, d-fructose, d-ribose, d-arabinose, d-xylose and 2-deoxyd-glucose by diperiodatoargentate(III) (DPA) have been investigated in alkaline medium. The order of the reaction with respect to [DPA] is unity while the order with respect to [sugar] is < 1 over the concentration range studied. The rate increases with an increase in [OH ^–] and there is a marginal decrease in the rate with an increase in [IO _inf4 ^sup– ]. No significant dependence on ionic strength was found, but the rate increases with a decreasing dielectric constant. Formic acid and the corresponding aldonic acids were detected as the products of oxidation. The participation of the open chain form of the sugar and a mechanism involving the initial formation of a complex between the enediol of the sugar and Ag^III are proposed.     

Ruthenium(III) catalysed oxidation of l-leucine by a new oxidant,diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of Ru(III) catalysed oxidation of l-leucine by diperiodatoargentate(III) (DPA) in alkaline medium at 298 K and a constant ionic strength of 0.60 mol dm⁻³ was studied spectrophotometrically. The oxidation products are pentanoic acid and Ag(I). The stoichiometry is [l-leucine]:[DPA] = 1:2. The reaction is of first order in Ru(III) and [DPA] and has less than unit order in both [l-leu] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Ru(III)–l-leucine complex, which further reacts with one molecule of monoperiodatoargentate(III) (MPA) in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectral studies. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant (K_c) was also calculated for the Ru(III) catalysed reaction at different temperatures. From the plots of log K_c versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to the slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. The active species of catalyst and oxidant have been identified.     

Kinetics and mechanism of the oxidation of a ferrous complex with an α,α′-diimine chelate ligand by ceric sulfate in aqueous acidic medium by UV-vis absorption spectroscopy

Kinetics of the oxidation of tris(2,2′-bipyridine)iron(II) sulfate by ceric sulfate was spectrophotometrically studied in an aqueous sulfuric acid medium. Different methods, including isolation, integration and half-life, were employed to determine the reaction order. The redox reaction was found to be first-order with respect to the reductant, tris(2,2′-bipyridine)iron(II) sulfate, and the oxidant, ceric sulfate. Complex kinetics was observed with an increase in the initial concentration of the oxidant. The influence of the dielectric constant, [H⁺] and [SO₄ ^2-] on the rate was also investigated. The increase in the dielectric constant and H⁺ ion concentration of the medium retard the rate, while an increase in the SO₄ ^2- ion concentration first accelerates the rate, and then retards the reaction. The effect of each factor, i.e., the dielectric constant, H⁺ ions and SO₄ ^2- ions, suggests that Ce(SO₄)₃ ^2- is the active species of cerium(IV). A rate law consistent with the observed kinetic data and the proposed mechanism is suggested to be: {fx631-1     

Mechanism and kinetics of the 2,2′-bipyridyl catalysis of the chromium(VI) oxidation of malic acid

A spectrophotometric study of the kinetics and mechanism of the oxidation of malic acid (Mal) by chromium(VI) catalyzed by 2,2′-bipyridyl (bpy) in aqueous acidic medium was conducted in a temperature range of ～298 to 313 K. This reaction was found to be pseudo-first order with respect to Cr(VI) and first order with respect to malic acid. Under the conditions of the pseudo-first order ([Mal]_o ? [Cr(VI)]_o), the observed rate constant (k _obs) increased with the increase in [H⁺] and [bpy]. There was a weak negative salt effect. Based on the experimental results, a possible reaction mechanism for this oxidation catalyzed by bpy is proposed. The rate equation derived from this mechanism can explain all the experimental phenomena.     

Kinetics and Mechanism of Oxidation of Sarcosine by Diperiodatocuprate(III) Complex in Alkaline Medium

The kinetics of oxidation of sarcosine by diperiodatocuprate(III) (DPC) was studied with spectrophotometry in a temperature range of 292.2–304.2 K. The reaction between diperiodatocuprate(III) and sarcosine in alkaline medium exhibits 1:1 stoichiometry (DPC:sarcosine). The reaction was found to be first order with respect to both DPC and sarcosine. The observed rate constant (k_obs) decreased with the increase of the [IO^?₄], decreased with the increase of the [OH^?], and then increased with the increase of the [OH^?] after a turning point. There was no salt effect, and free radicals were detected. Based on the experimental results, a mechanism involving the diperiodatocuprate(III) (DPC) as the reactive species of the oxidant has been proposed. The activation parameters, as well as the rate constants of the rate‐determining step, have been calculated.     

Thermodynamic quantities for the different steps involved in the mechanism of osmium(VIII) catalysed oxidation of l-lysine by a new oxidant,diperiodatoargentate(III) (stopped flow technique)

The kinetics of Os(VIII) catalysed oxidation of l-lysine by diperiodatoargentate(III) (DPA) in alkaline medium at T = 298 K and a constant ionic strength of 0.50 mol · dm^?3 was studied spectrophotometrically. The oxidation products are aldehyde (5-aminopentanal) and Ag(I). The stoichiometry is i.e. [l-lysine]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)] and [DPA] and is less than unit order in both [l-lys] and [alkali]. Addition of periodate has no effect on the reaction. Effect of added products, ionic strength, and dielectric constant of the reaction medium have been investigated. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)-l-lysine complex, which further reacts with one molecule of deprotonated DPA in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, and GC-MS. The reaction constants involved in the different steps of the mechanism are calculated at different temperatures. The catalytic constant (K_C) was also calculated at different temperatures. From the plots of lg K_C versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. The active species of catalyst and oxidant have been identified.     

Oxidation of L-phenylalanine by diperiodatoargentate(III) in aqueous alkaline medium. A Mechanistic approach

The kinetics of oxidation of L-phenylalanine (L-Phe) by diperiodatoargentate(III) (DPA) in alkaline medium at a constant ionic strength of 0.25 mol/dm⁻³ has been studied spectrophotometrically. The reaction between DPA and L-phenylalanine in alkaline medium exhibits 1: 1 stoichiometry (L-phenylalanine: DPA). The reaction shows first order in [DPA] and has less than unit order dependence each in both [L-Phe] and [Alkali] and retarding effect of [IO₄⁻] under the reaction conditions. The active species of DPA is understood to be as monoperiodatoargentate(III) (MPA). The reaction is shown to proceed via a MPA-L-Phe complex, which decomposes in a rate-determining step to give intermediates followed by a fast step to give the products. The products were identified by spot and spectroscopic studies. The reaction constants involved in the different steps of the mechanisms were calculated. The activation parameters with respect to slow step of the mechanism were computed and discussed. The thermodynamic quantities were also determined for the reaction.     

Effect of Anionic Surfactant on the Oxidation of DL-Aspartic Acid by N-Bromophthalimide: A Kinetic Study

The kinetics of oxidation of DL-Aspartic acid (Asp) by N-bromophthalimide (NBP) was studied in the presence of sodium dodecyl sulfate (SDS) in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Asp] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant, that is, [Phthalimide] has decreased the rate of reaction. The rate of reaction increased with increase in inorganic salts concentration, whereas a change in [Cl^?], ionic strength of the medium and [Hg(OAc)₂] had no effect on the oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. COOH-CH₂-CN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable reaction mechanism consistent with the experimental findings has been proposed. The micelle-binding constant has been calculated.     

Oxidations by iron(VI). Kinetic study of uncatalysed and osmium(VIII) catalysed oxidation of dimethyl sulphoxide in alkaline medium

Summary Uncatalysed and Os^VIII-catalysed oxidation of dimethyl sulphoxide (DMSO) by potassium ferrate [Fe^VI] has been studied in alkaline medium in the 9.8–11.9 pH range, in the presence of IO ₄ ^– as a stabilizing agent. The order in [Fe^VI] and [DMSO] was found to be unity for the uncatalysed reaction and zero and fractional respectively for the catalysed reaction. The [Os^VIII] order was unity in the catalysed reaction. The rate of oxidation decreased with increase in pH and the order in [H⁺] was fractional for the uncatalysed oxidation. However in the catalysed oxidation, the rate at first decreased and then increased with increase in pH. The effect of changing [IO ₄ ^– ] and [buffer] on the oxidation rate was negligible in both cases. Suitable mechanisms consistent with the observed kinetics have been proposed.     

Free-radical-mediated oxidation of ascorbic acid by peroxomonosulphate

The kinetics of the oxidation of ascorbic acid (AH₂) by peroxomonosulphate (PMS) were determined in aqueous medium in acidic (pH 4.4), neutral (pH 7.0) and alkaline (pH 9.0) conditions over the temperature range 13-28°C. The reactions were found to obey total second-order kinetics, first-order each with respect to peroxomonosulphate and ascorbic acid concentration, obeying-d[AH₂]/dt = k ₂[PMS][AH₂]. Dehydroascorbic acid was detected as the product of the reaction. The stoichiometry of the reaction, [peroxomonosulphate]/[ascorbicacid] = 1 : 1, indicated the absence of self-decomposition of peroxomonosulphate. The influence of neutral salt (NaClO₄) was found to increase the reaction rate. Evidence for the formation of radical intermediates was obtained. A mechanism involving the formation of hydroxyl, sulphate and ascorbate free radicals as intermediates is proposed. The rate and activation parameters were evaluated to substantiate the mechanism proposed. A comparison is made with the corresponding reactions of the similar peroxides, S₂O₈ ^2- and P₂O₈ ^4-.     

Kinetic Study of Oxidation of DL-Serine by N-Bromophthalimide in the Presence of Sodium Dodecyl Sulfate

The kinetics of oxidation of DL-serine (Ser) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ser] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant [Phthalimide] and [Hg(OAc)₂] has no effect on the rate of reaction. The change in ionic strength of the medium had no effect on oxidation velocity. The rate of reaction increased with increasing [Br^?] and decreased with increasing [Cl^?]. The rate of reaction decreased with decrease in dielectric constant of the medium. OHCH₂CN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable mechanism consistent with the experimental findings has been proposed. The micelle-binding constant has been calculated.     

Kinetics and mechanism of oxidation of L-Alanine by <Emphasis Type="Italic">N</Emphasis>-bromophthalimide in the presence of sodium dodecyl sulfate

The kinetics of oxidation of L-Alanine (Ala) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ala] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant [Phthalimide] has decreased the rate of reaction. The rate of reaction increased with increase in inorganic salts concentration i.e., [Cl⁻] and [Br⁻], whereas a change in ionic strength of the medium and [Hg(OAc)₂] had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. CH₃CN was identified as the main oxidation product of the reaction. The various activation parameters have been computed and suitable mechanism consistent with the experimental findings has also been proposed. The micelle-binding constant has been calculated. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 386–396. The article is published in the original.     

Studies of Unusual Oxidation States of Transition Metals Ⅱ——Kinetics and Mechanism of Oxidation of Pyruvate by Diperiodatoargentate (Ⅲ)Ion

The kinetics of oxidation of pyruvate by diperiodatoargentate( III) ion (DPA) has been studied spec-trophotometrically in alkaline medium. It was found that the reaction order with respect to both DPA and pyruvate is unity and the rate equation can be expressed asThe rate increases with the increase in [OH ] and decreases with the increase in [periodate]. There is a positive ionic strength effect in this reaction system. A mechanism has been proposed to explain the experimental results. The observed activation parameters are presented.     

Mechanistic studies of oxidation of maltose and lactose by [H2OBr]+ in presence of chloro-complex of Rh(III) as homogeneous catalyst

Kinetic studies in homogeneously Rh(III)-catalyzed oxidation of reducing sugars, i.e. maltose and lactose, by N-bromoacetamide (NBA) in the presence of perchloric acid have been made at 40 °C using mercuric acetate as Br⁻ ion scavenger. The results obtained for the oxidation of both reducing sugars show first-order dependence of the reactions on NBA at its low concentrations, which shifts towards zero-order at its higher concentrations. First-order kinetics in [Rh(III)] and zero-order kinetics in [reducing sugar] were observed. Positive effect of [Cl⁻] was observed in the oxidation of both maltose and lactose. Order of reaction was found to be one and half (1.5) throughout the variation of [H⁺] in the oxidation of both maltose and lactose. An increase in the rate of reaction with the decrease in [Hg(OAc)₂] and [NHA] was observed for both the redox systems. The rate of oxidation is unaffected by the change in ionic strength (μ) of the medium. The main oxidation products of the reactions were identified as formic acid and arabinonic acid in the case of maltose and formic acid, arabinonic acid and lyxonic acid in the case of lactose. A common mechanism for the oxidation of both maltose and lactose, showing the formation of most reactive activated complex, [RhCl₄(H₃O)H₂OBr]⁺, and an unreactive complex, [RhCl₄(H₂O)(H₂OBrHg)]²⁺, has been proposed. Various activation parameters have also been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.     

Diperiodatoargentate(III) Oxidation of D-Galactose in Absence and Presence of Anionic and Cationic Surfactants

Diperiodatoargentate(III) (DPA) was used as an oxidizing titrant in the spectrophotometric degradation of D-galactose for the first time. The kinetics is based on the reduction of silver(III) to silver(I) by D-galactose at specified experimental conditions. Effects of added [H⁺] and [periodate] have also been investigated. The premicellar environment of cetyltrimethylammonium bromide (CTAB) and sodiumdodecyl sulphate (SDS) strongly inhibits the reaction rate. The observed rate constant is strongly affected by [CTAB] and [SDS] changes for [surfactant] <cmc. Surfactant concentration range above the cmc does not influence the reaction rate. The monoperiodatoargentate(III) ions act as an active oxidant in comparison to that of DPA. A suitable mechanism involving a two-electron transfer from D-galactose to the silver(III) species has been proposed and hence a corresponding rate equation has been derived.     

Cu(II) promoted oxidation of L-valine by hexacyanoferrate(III) in cationic micellar medium

The kinetics of Cu(II) accelerated L-valine (Val) oxidation by hexacyanoferrate(III) in CTAB micellar medium were investigated by measuring the decline in absorbance at 420 nm. By adjusting one variable at a time, the progression of the reaction has been inspected as a function of [OH⁻], ionic strength, [CTAB], [Cu(II)], [Val], [Fe(CN)₆³⁻], and temperature using the pseudo-first-order condition. The results show that [CTAB] is the critical parameter with a discernible influence on reaction rate. [Fe(CN)₆]^3- interacts with Val in a 2:1 ratio, and this reaction exhibits first-order dependency with regard to [Fe(CN)₆³⁻]. In the investigated concentration ranges of Cu(II), [OH⁻], and [Val], the reaction demonstrates fractional-first-order kinetics. The linear increase in reaction rate with added electrolyte is indicative of a positive salt effect. CTAB significantly catalyzes the process, and once at a maximum, the rate remains almost constant as [CTAB] increases. Reduced repulsion between surfactant molecules' positive charge heads brought on by the negatively charged [Fe(CN)₆]^3-, OH⁻, and [Cu(OH)₄]^2- molecules may be responsible for the observed drop in CMC of CTAB.     

Kinetic and mechanistic studies on the oxidation of pyrrolidine by bis(hydrogenperiodato)argentate(III) complex anion

The kinetics of oxidation of pyrrolidine by bis(hydrogenperiodato)argentate(III) complex anion ([Ag(HIO₆)₂]^5?) was studied in alkaline medium, with reaction temperatures in the range of 15.0–30.0 °C. The experiments indicated that the oxidation follows an overall second-order reaction, being first-order in both Ag(III) and pyrrolidine. The observed second-order rate constants, k′, decreased with increasing [IO₄ ^?] but increased slightly with increasing [OH^?]. The influence of ionic strength on the reaction rate was also investigated. The oxidation resulted in oxidative deamination of pyrrolidine, giving 4-hydroxybutyrate as the product. A reaction mechanism is proposed which includes an equilibrium between [Ag(HIO₆)₂]^5? and [Ag(HIO₆)₂(OH)(H₂O)]^2?; these two Ag(III) species are reduced by pyrrolidine in parallel rate-determining steps. The rate equation derived from the proposed mechanism can explain the experimental observations. The rate constants of the rate-determining steps, together with the associated activation parameters, were calculated accordingly.