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Kinetics and Mechanism of Oxidation of Bromate by Diperiodatonickelate(IV) in Aqueous Alkaline Medium--A Simple Method for Formation of Perbromate
Abstract
The kinetics of oxidation of bromate by diperiodatonickelate(IV) (DPN) in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between DPN and bromate in alkaline medium exhibits 1:1 stoichiometry (DPN:bromate). The reaction shows first order dependence on [DPN] and zero order dependence in [bromate] and less than unit order dependence in alkali concentrations. Periodate has a retarding effect on the rate of reaction. Reaction rate increases with increase in ionic strength and decrease in solvent polarity of the medium. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the monoperiodatonickelate(IV) (MPN) as the reactive species of the oxidant has been proposed. The reaction constants involved in the mechanism are evaluated. The activation parameters were computed with respect to the slow step of the mechanism.
The oxidation of Rizatriptan by diperiodatoargentate(III) has been studied by spectrophotometry at neutral pH. The kinetics of the reaction of Rizatriptan has been shown to principle of non-complementary oxidation steps. The initial step involves the deprotonated of the diperiodatoargentate(III) with the alkali; this rearranges during the displacement of a ligand to give free periodate and takes up another ligand monoperiodateargentate(III), combines with a substrate to endow with an intermediate complex which decomposes within a slow step to provide the final product in the following step with a first-order rate constant. The main product was identified by spot test, Fourier- transform infrared spectroscopy, Nuclear magnetic resonance and Liquid chromatography-mass spectrometry spectrum. A conceivable mechanism including pre equilibrium of adducts development between the complex and reductant was planned from the kinetics study. The rate conditions got from system can clarify all exploratory phenomena, and the activation parameters alongside rate constants of the rate determining step were ascertained.
The kinetics of oxidation of L-proline by diperiodatonickelate(IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm -3 was studied spectrophotometrically. The reaction is of first order in [DPN], zero order in [alkali] and less than unit order in [L-proline]. Addition of periodate has no effect on the rate of reaction. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The main products were identified by spot test and IR spectra. A mechanism involving the diperiodatonickelate(IV) (DPN) as the reactive species of the oxidant has been proposed. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated. The isokinetic temperature was determined and discussed.
The kinetics of oxidation of L-glutamine by diperiodatonickelate (IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 0.5 mol dM -3 has been studied spectrophotometrically. The reaction is first order in [DPN] and is an apparent less than unit order, each in [L-glutamine] and [alkali] under the experimental conditions. However, the order in [L-glutamine] and [alkali] changes from first order to zero order as the concentrations change from lower to higher concentrations. Addition of periodate has no effect on the rate of reaction. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. A mechanism involving the deprotonated diperiodatonickelate(IV) as the reactive species of the oxidant has been proposed. The reaction constants involved in the different steps of mechanism are evaluated and thermodynamic quantities are also calculated.
A mechanism involving deprotonated diperiodatonickelate(IV) (DPN) as the reactive species of the oxidant has been proposed. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to slow the step of the mechanism are computed and discussed.
The kinetics of the osmium (Os(VIII)) catalyzed oxidation of xylitol (XYL) by a silver(III) periodate complex (diperiodatoargentate(III)) (DPA) in an aqueous alkaline medium at 298 K and at a constant ionic strength of 0.06 mol dm−3 was studied spectrophotometrically. The reaction between DPA and xylitol in an alkaline medium exhibits 1:2 stoichiometry (XYL:DPA). The reaction is of first order in [Os(VIII)] and [DPA] and has a negative fractional order in [IO4−]. It is apparent that it has less than the unit order in [XYL] and [OH−] under the experimental conditions. The main oxidation product was identified as 2,3,4,5-tetrahydroxypentanoic acid by FT-IR and LC-MS spectral studies. A probable mechanism was proposed and discussed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. The active species of the catalyst and oxidant have been identified.
The oxidation of xylitol (XYL) by Ag (III) periodate complex (DPA) in aqueous alkaline medium at 298 K and a constant ionic strength of 0.06 mol dm was studied spectrophotometrically. The reaction between xylitol and DPA in alkaline medium exhibits 1:2 stoichiometry in the reaction. The order of the reaction with respect to [DPA] was unity while the apparent order with respect to [XYL] was less than unity over the concentration range studied. The rate of the reaction increased with increase in [OH] whereas the rate decreased with increase in [IO]. The main products were identified by FT-IR and LC-MS spectral studies. The probable mechanism was proposed. The activation parameters with respect to slow step of the mechanism were computed and are discussed. Thermodynamic quantities were also calculated. Kinetic studies suggest that [Ag (H2IO6) (H2O) 2] is the reactive species of Ag (III).
The kinetics of oxidation of ruthenium(III)-catalysed oxidation of 4-hydroxycoumarin (HDC) by diperiodatonickelate(IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 1.0moldm−3 was studied spectrophotometrically. The reaction between DPN and 4-hydroxycoumarin in alkaline medium exhibits 3:1 stoichiometry (DPN:HDC). The reaction is of first order in [DPN] and less than unit order in [HDC] and [alkali]. Periodate has no effect on the rate of reaction. The reaction rate increases with increase in ionic strength and decrease in dielectric constant of the medium. The main products were identified by spot test and spectral studies. A mechanism involving the DPN as the reactive species of the oxidant and a complex formation between 4-hydroxycoumarin and ruthenium(III) species has been proposed. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.
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 kinetics of ruthenium(III)-catalysed oxidation of paracetamol by diperiodatonickelate(IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 1.0 mol dm−3 was studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 1:2 stoichiometry (DPN:paracetamol). The reaction shows first order dependence on [DPN] and [ruthenium(III)] and (apparent) less than unit order in both [paracetamol] and [alkali] under the experimental conditions. However, the order in [paracetamol] and [alkali] changes from first order to zero order as the concentrations change from lower to higher concentrations. Addition of periodate has a retarding effect on the reaction. The effects of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The main products were identified by spot test, IR and NMR. A mechanism involving the monoperiodatonickelate(IV) (MPN) as the reactive species of the oxidant has been proposed. The active species of ruthenium(III) is understood as [Ru(H2O)5OH]2+. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.
Oxidation of sulfacetamide (SUL), a sulfonamide drug by alkaline diperiodatoargentate(III) (DPA), a powerful oxidizing agent at 298 K and at a constant ionic strength of 0.50 mol/dm3, has been carried out spectrophotometrically at 360 nm. The results indicate that 3 mol of DPA consumed 1 mol of SUL (3:1). The oxidation product has been separated and characterized by IR and NMR spectral studies. The reaction is first order in [DPA] and has less than unit order in [SUL]. The rate constants increased with an increase in alkali concentration and decreased with increase in [IO4−]. Ionic strength and dielectric constant of the medium had negligible effect on the reaction rate. A mechanism has been proposed which explains the observed orders and experimental observations. Monoperiodatoargentate(III) (MPA) has been considered as the active species for the title reaction. The reaction proceeds through a SUL:MPA complex which decomposes in a slow step to give the p-hydroxylamine benzenesulfonamide and Ag(I) species. Further oxidation in the subsequent fast steps yeilds nitroso and nitro derivative of benzenesulfonamide, each transformation consuming 1 mol of MPA. 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, and thermodynamic quantities are also determined. The probable active species of oxidation have been identified.
A theory is developed which relates the rate constant of a reaction to the dielectric constant of the solvent. It is applicable to reactions that are of such a character that the electrostatic interactions are more important than non-electrostatic ones, such as ion-ion, ion-dipole and certain dipole-dipole reactions. The theory is based on the Kirkwood expression for the activity coefficient of a spherical solute molecule bearing a particular distribution of charges. The resulting equation predicts a linear dependence of the logarithm of the rate constant on the reciprocal of the dielectric constant; the proportionality constant depends on the net charges on the reactant molecules and also on the distribution of charges in the reactant molecules and the activated complex. An experimental study has also been made of the acid and base hydrolyses of acetamide and propionamide in various alcohol + water mixtures. The rates are found to increase with increasing dielectric constant. The results of this study, together with data in the literature for the effect of solvent on the acid and base hydrolyses of esters and anilides, are then used as a test of the theory. Specific models are proposed for the activated complexes formed in each case, consistent with various lines of experimental evidence. The procedure used for testing the theory is to calculate values of radii of activated complexes which are required to give the experimental slopes of plots of log k against 1/D. The values obtained are all within a reasonable range.
The kinetics of reduction of a nickel(IV) oxime complex by ascorbate ion to give the corresponding nickel(II) species are reported. Ascorbate ion is the sole reductant with second-order rate constants 3.02 × 105 dm3 mol–1 s–1 and 1.36 × 104 dm3 mol–1 s–1 for reactions with protonated and unprotonated forms of the oxidant respectively at 25.0 °C and 0.10 mol dm–3 ionic strength. The origin of the protonation of nickel(IV), pKh 3.70, is discussed. Electron spin resonance experiments suggest that the redox mechanism involves two discrete one-electron transfer steps with formation of a nickel(III)–oxime intermediate. The first step in the reduction goes by an outer-sphere pathway and a self-exchange rate around 104 dm3 mol–1 s–1 is calculated for the NiIV–NiIII couple. Studies with optically active solutions of nickel(IV) show no chiral discrimination in the reaction.
The title reaction was investigated in aqueous alkaline medium. A first order dependence on both [diperiodatonickelate(IV)]
and [OH−] and an apparent fractional order in [1,10-Phenanthroline] was obtained. Addition of the reaction product has no effect on
the reaction. The effects of dielectric constant, ionic strength, and temperature on the rate of the reaction were studied.
A mechanism based on the experimental results is proposed, and the constants involved in the mechanism were evaluated. A good
agreement between the observed and calculated rate constants at varying experimental conditions was obtained.
The reaction between Thymol Blue (TB) and bromate in the presence of sulfuric acid has been studied by monitoring the depletion kinetics of TB. The reaction exhibits complex kinetic behaviour. Under excess bromate and acid conditions, the reaction was initially fast and was followed by a kinetically controlled slow reaction. After an induction period, the reductant again underwent a rapid depletion. The kinetic data were analysed by determining the reaction rates under the two rapid depletion conditions and by estimating the induction time between the two rapid depletion stages. Under the initial conditions the rate-limiting step was found to be first order with respect to H+, bromate and TB. The overall potential of the reaction increased continuously with the progress of the reaction. The concentration of bromide dropped initially and built up slowly reaching a maximum before decreasing rapidly with corresponding fast depletion of Thymol Blue. At low bromate concentration TB reacted with bromate with a stoichiometric ratio of 3 : 2, but with excess bromate the ratio increased to 4 : 5. The kinetics of the reaction beween Thymol Blue and aqueous bromine were monitored by a stopped-flow technique. The probable reaction mechanism with bromide acting as an autocatalyst is discussed.
The oxidation of antimony(III) by hexacyanoferrate(III) has been studied in alkaline media. A microamount of chromium(III)(10–6 mol dm–3) is sufficient to catalyse the reaction. The active species of catalyst and oxidant in the reaction are understood to be [Cr(OH)4]– and [Fe(CN)6]3–. The autocatalysis exhibited by one of the products, i.e. antimony(V), is attributed to complex formation between antimony(V) and [Fe(CN)6]3–. A composite mechanism and rate law are proposed. The reaction has been utilised for the analysis of chromium(III) in the range 5.2 ng cm–3–1.14 µg cm–3.