- Kinetics of the Oxidation of chromium(III) by Periodate
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The kinetics of oxidation of III(H2O)(TOH)>, (TOH=N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetate) by periodate in aqueous solutions has been found to obey the following equation: where k2 is the rate constant for
- Abdel-Khalek, Ahmed A.,Elsemongy, Mahmoud M.
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- Photochemically induced autocatalysis in the chlorate ion-iodine system
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Light initiates an autocatalytic reaction sequence in the chlorate ion-iodine reaction. A previous report on the same system (Oliveira, A. P.; Faria, R. B. J. Am Chem. Soc. 2005, 127, 18022-18023.) failed to recognize the role of photoinitiation by the diode-array spectrophotometer used in the experiments. A mechanism is proposed to interpret the observations. Copyright
- Galajda, Monika,Lente, Gabor,Fabian, Istvan
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- Disproportionation Kinetics of Hypoiodous Acid As Catalyzed and Suppressed by Acetic Acid-Acetate Buffer
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The kinetics of the disproportionation of hypoiodous acid to give iodine and iodate ion (5HOI ? 2I2 + IO3- + H+ + 2H2O) are investigated in aqueous acetic acid-sodium acetate buffer. The rate of iodine formation is followed photometrically at -log [H+] = 3.50, 4.00, 4.50, and 5.00, μ = 0.50 M (NaClO4), and 25.0°C. Both catalytic and inhibitory buffer effects are observed. The first process is proposed to be a disproportionation of iodine(I) to give HOIO and I-; the iodide then reacts with HOI to give I2. The reactive species (acetato-O)iodine(I), CH3CO2I, is postulated to increase the rate by assisting in the formation of I2O, a steady-state species that hydrolyzes to give HOIO and I2. Inhibition is postulated to result from the formation of the stable ion bis(acetato-O)iodate-(I), (CH3CO2)2I-, as buffer concentration is increased. This species is observed spectrophotometrically with a UV absorption shoulder (λ = 266 nm; ∈ = 530 M-1 cm-1). The second process is proposed to be a disproportionation of HOIO to give IO3- and I2. Above 1 M total buffer, the reaction becomes reversible with less than 90% I2 formation. Rate and equilibrium constants are resolved and reported for the proposed mechanism.
- Urbansky, Edward T.,Cooper, Brian T.,Margerum, Dale W.
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- Pitfall of an initial rate study: On the kinetics and mechanism of the reaction of periodate with iodide ions in a slightly acidic medium
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The kinetics of the periodate-iodide reaction has a contradictory history dating back to almost a century. This reaction has been reinvestigated spectrophotometrically in the pH range 3.13-5.55 in both buffered (acetic acid/acetate) and unbuffered solution at T = 25.0 ± 0.1 °C with an I = 0.5 M ionic strength. The spectra between 290 and 500 nm were recorded and the reaction was followed until at least 95% of one of the reactants was consumed. The stoichiometry has been found to be strongly dependent on pH, but the rate of the initial step is independent of pH within the pH range studied. An eight-step kinetic model is proposed with four fitted kinetic parameters to take all the important characteristics of the experimental curves into account. On the basis of the model, a perfect reconciliation of the previous contradictory results is presented. It is shown that the kinetic parameters obtained from the initial rate of formation of a product unavoidably leads to misinterpretation of the results in the case of a branching mechanism (and stoichiometry).
- Horvath, Attila K.
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- Oxidation of hexaaquoiron(II) by periodate in aqueous acidic solution
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The oxidation of Fe(II) by periodate in aqueous acidic solutions obeys the rate law (i) {A figure is presented} where [L6]T represents the total periodate concentration. The magnitudes of k0, k′1, k″2 and k3 are 0.235 sec-1, 120 sec-1, 7.5 ± 1.5 sec]-1, and (7.3 ± 0.5) X 104M-2 sec-1 respectively at 25 °C and I = 1.0 M. The terms in equation (i), that are first order in [L-]T, correspond to the oxidation process with possibly one-electron (term showing first order in [Fe(11)] and two electron-transfer (term showing second order in [Fe(II)]. At low [H+] (0.10 M), the pathway first order in [Fe(II)] predominates, whereas at high [H+] (0.80 M), the term second order in [Fe(II)] prevails. An explanation of the term independent of [L-]T is not quite obvious.
- El-Eziri,Sulfab, Yousif
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- Mechanism for the Oscillatory Bromate-Iodide Reaction
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A mechanism is proposed for the reaction between bromate and iodide ions in acidic solution.The mechanism consists of 13 elementary steps and involves the interhalogen compound IBr but does not contain any radical species.Extensive numerical simulations show that the mechanism gives good agreement with the observed clock behavior in batch and with the bistability and oscillations observed in a CSTR.The present system appears to be the first in which bistability between a stationary and an oscillatory state has been succesfully described by a mechanism consisting of elementary steps.
- Citri, Ofra,Epstein, Irving R.
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- Kinetics and Mechanism of the Chlorite-Periodate System: Formation of a Short-Lived Key Intermediate OClOIO3 and Its Subsequent Reactions
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The chlorite-periodate reaction has been studied spectrophotometrically in acidic medium at 25.0 ± 0.1 °C, monitoring the absorbance at 400 nm in acetate/acetic acid buffer at constant ionic strength (I = 0.5 M). We have shown that periodate was exclusive
- Baranyi, Nóra,Cseko, Gy?rgy,Valkai, László,Xu, Li,Horváth, Attila K.
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p. 2436 - 2440
(2016/03/19)
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- On the complexity of kinetics and the mechanism of the thiosulfate- periodate reaction
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The thiosulfate-periodate reaction has been studied spectrophotometrically in a slightly acidic medium at 25.0 ± 0.1 °C in an acetate/acetic acid buffer by monitoring the absorbance in the 250-600 nm wavelength range at a constant ionic strength adjusted by the buffer component sodium acetate. In agreement with a previous study, we found that the reaction cannot be described by a single stoichiometric equation, tetrathionate and sulfate are simultaneously formed, and its ratio strongly depends on the pH. As expected at certain initial concentration ratios of the reactants, the reaction behaves as a clock reaction, but after its appearance, iodine is slowly consumed mainly because of the moderate tetrathionate-iodine reaction. It is also enlightened that the initial rate of the reaction is completely independent of the pH, which apparently contradicts a previous study, which postulates a "supercatalytic" behavior of the hydrogen ion on the title reaction. Significant buffer assistance that may change the absorbance-time profiles was also observed. On the basis of the kinetic data, a robust 28-step kinetic model with 22 fitted parameters is proposed and discussed to explain adequately all of the important characteristics of the kinetic curves.
- Rauscher, Evelin,Cseko, Gyoergy,Horvath, Attila K.
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p. 5793 - 5802
(2011/07/29)
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- Photoinduced reaction between chlorine dioxide and iodine in acidic aqueous solution
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Photoinduced reaction between ClO2 and I2 has been discovered under illumination with 460 nm lightband. The photochemical reaction has a variable stoichiometry in acidic aqueous solution because the induced disproportionation of ClO2 to ClO3- and Cl- competes with the oxidation of I2 to IO3- by ClO2 in the illuminated reaction mixture. The reaction rate depends on the light power of illumination and on the concentration of I2, but it is independent of the concentration of ClO2. It is also independent of the pH in the range of 0-2.0 and of the ionic strength in the range of 0.01-1.0 M. Reversible dissociation of I2 has been identified as the primary photochemical process and rate-determining step in the mechanism. Reactive I atoms are considered to initiate fast reaction steps, leading to the formation of products through reactive intermediates such as IClO2, ClO, IO, and HOCl. This mechanism is proposed for explaining the photoresponses of the CDIMA oscillatory reaction system to the illumination with visible light.
- Rabat, Gyula,Kovacs, Klara M.
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p. 6167 - 6170
(2007/10/03)
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- A new type of oxyhalogen oscillator: The bromite-iodide reaction in a continuous flow reactor
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The reaction between bromite and iodide ions in a flow reactor shows two steady states and sustained oscillations in pH, redox potential, and [I-]. The oscillatory behavior is extremely sensitive to the inflow ratio [BrO2-]/[I-], the flow rate, the initial pH of the input solutions, and the stirring rate. Batch experiments suggest that the system behaves in several respects like the analogous chlorite-iodide oscillator. The bromite-iodide system, however, is also a pH oscillator and is the first oxyhalogen oscillator to oscillate in the neutral and basic pH range.
- Orbán, Miklós,Epstein, Irving R.
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p. 1252 - 1256
(2007/10/02)
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- Oxidation of Hydroxylamine by Periodate in a Continuous-Flow Stirred Tank Reactor: A New pH Oscillator
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The periodate oxidation of hydroxylamine exhibits a complex and variable stoichiometry at pH 5.There are two limiting cases.In excess periodate the products are nitrate and iodate, while in a large excess of hydroxylamine IO4- is reduced to I-, and the nitrogen-containing product is N2O.The formation of nitrite ion and iodine is important when neither of the reactants is present in large excess.The reaction shows clock type kinetics in closed conditions if no buffer is present.In a flow reactor sustained oscillations in +>, in color, and in redox potential are found experimentally in a narrow range of flow rate and input concentrations.A simple model is proposed to explain the oscillation.
- Rabai, Gyula,Epstein, Irving R.
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p. 7556 - 7559
(2007/10/02)
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- Iodine chemistry in the +1 oxidation state. II. A Raman and uv-visible spectroscopic study of the disproportionation of hypoiodite in basic solutions
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The kinetics of disproportionation of elemental iodine to iodide and iodate ions has been studied in basic aqueous media using Raman and uv-visible spectroscopy.The IO streching vibrations for IO- and I2OH- were observed at 430 +/- 2 and 560 +/- 2 cm-1, respectively.The totally symmetric streching vibration for IO2- was observed at 685 +/- 2 cm-1.The Raman results indicate that I2OH- is a linear molecule with a stronger I-O bond than IO-.The rate expression at 25 deg C in 1 mol dm-3 NaOH was found to be .The reaction is primarily a reaction of the iodine +1 oxidation-state species IO- and I2OH-.It proceeds through the +3 oxidation-state species IO2-.The following equilibrium and rate constants were determined. .
- Wren, J. C.,Paquette, J.,Sunder, S.,Ford, B. L.
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p. 2284 - 2296
(2007/10/02)
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- Iodine chemistry in the +1 oxidation state. I. The electronic spectra of OI-, HOI, and H2OI+
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Electronic spectra are reported for the hypoiodite ion (OI-), hypoiodous acid (HOI), and its conjugate acid (H2OI+) in aqueous media.Iodine in the +1 oxidation state was produced by either of the two rapid reactions HOCl + I- HOI + Cl- or ICl(g) + H2O HOI + Cl- + H+.Spectroscopic evidence of the disproportionation of OI-/HOI/H2OI+ to iodide and iodate in basic media, and to iodine and iodate in acid media, was obtained.The results are consistent with previously reported values for the pKa of HOI and H2OI+.
- Paquette, Jean,Ford, Beverly L.
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p. 2444 - 2448
(2007/10/02)
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- Study of (Tetraphenylporphinato)manganese(III)-Catalyzed Epoxidation and Demethylation Using p-Cyano-N,N-dimethylaniline N-Oxide as Oxygen Donor in a Homogeneous System. Kinetics, Radiochemical Ligation Studies, and Reaction Mechanism for a Model of Cytochrome P-450
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Oxygen transfer from p-cyanodimethylaniline (p-CNDMANO) to cyclohexene as well as "intramolecular" oxygen transfer accompained by demethylation to yield p-cyanomonomethylaniline (p-CNMMA) are strongly catalyzed by ligated (tetraphenylporphinato)MnIII (i.e., XMnIIITPP).These reactions have been studied in dry, oxygen-free benzonitrile.Radiochemical studies show that H2O (or TOH) is not bound to XMnIIITPP in aprotic solvents so that the MnIII moiety is pentacoordinate.Oxygen transfer occurs through the reversible formation of the hexacoordinated species p-CNDMANO*MnIII(X)TPP.This species decomposes to p-cyanodimethylaniline (p-CNDMA) + O=MnV(X)TPP.Reactions of cyclohexene with O=MnV(X)TPP yields cyclohexene epoxide and XMnIIITPP whereas p-CNMMA is formed directly from the p-CNDMANO*MnIII(X)TPP complex.The rates of product formation are shown to be dependent upon the nature of the ligand (X- = F-, Cl-, Br-, I-, OCN-).In the absence of the axial ligand X-, the rates of reaction are extremely slow.Thus, the MnIII C2-cap-porphyrin (XMnIIICAPTPP), which can only form an O=MnV porphyrin species wherein the Mn moiety is not complexed to X- as a sixth ligand, shows almost no tendency to act as a catalyst for oxygen transfer.The necessary presence of the axial ligand X- and the dependence of rate upon X- requires the structure of the oxygen transfer species to be quivalent to O=MnV(X)TPP.A kinetic analysis is presented (Scheme III) which has allowed the determination of the influence of the ligands X- upon the various rate constants (Table IV) involved in the overall oxidations.By employing p-CNDMANO as oxygen donor, multiple catalytic turnovers without loss of porphyrin have been realized.
- Powell, Michael F.,Pai, Emil F.,Bruice, Thomas C.
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p. 3277 - 3285
(2007/10/02)
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- Kinetics and mechanism of the oxidation of iodine by chlorite ion
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The stoichiometry of the reaction between chlorite and iodine in the pH range 2-5 and at low [I-] has been determined to be 5ClO2- + 2I2 + 2H2O → 5Cl- + 4IO3- + 4H+. The kinetics of this reaction have been studied by stopped-flow spectrophotometry at 22.2°C and variable ionic strength (10-2-10-1 M). The rate law is -1/2d[I2]/dt = (k1[ClO2-] + k2[ClO2-]/[H+] + k3)[I2], where k1, = (1.1 ± 0.4) × 10 M-1 s-1, k2 = (1.1 ± 0.1) × 10-2 s-1, and k3 = (5.4 ± 0.3) × 10-1 s-1. A mechanism is proposed involving formation of the key intermediate IClO2 by reactions between chlorite and I2, I2OH-, and IOH2+. The rate constant for the elementary reaction ClO2- + I2 → IClO2 + I- is given by k1. The value of the rate constant for the elementary reaction I2OH- + ClO2- → IClO2 + I- + OH- is 7.7 × 107 M-1 s-1. We have identified k3 with the reaction I2 + H2O → IOH2+ + I-.
- Grant, John L.,De Kepper, Patrick,Epstein, Irving R.,Kustin, Kenneth,Orbán, Miklós
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p. 2192 - 2196
(2008/10/08)
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- KINETICS OF THE HYDROLYSIS OF IODINE IN WATER-ETHANOL MEDIA
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The kinetics of hydrolysis of iodine has been studied in borate buffer solutions and in mixtures of them with ethanol.The rate of reaction was followed potentiometrically by measuring of the voltage of a cell glass electrode //H(1+), I2, I(1-), IO3// Pt-electrode.On the basis of the obtained data a mechanism has been proposed according to which iodine exists in a solution in form of Ix associates, and the slowest step of hydrolysis is the reaction of iodine molecules with water.
- Juznic, K.
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