- Electron Affinity of Chlorine Dioxide
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The flowing afterglow technique was used to determine the electron affinity of chlorine dioxide.A value of 2.37+/-0.10 eV was found bracketing between the electron affinities of HS and SF4 as a lower limit and that of NO2 as an upper limit.This value is in excellent agreement with 2.32 eV predicted from a simple thermodynamic cycle involving the reduction potential of the ClO2/ClO2- couple and a Gibbs hydration energy identical with that of SO2-.
- Babcock, L. M.,Pentecost, T.,Koppenol, W. H.
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- OXIDATION OF TRIS(1,10-PHENANTHROLINE)IRON(II) BY CHLORINE DIOXIDE.
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The reaction of left bracket Fe(phen)//3 right bracket **2** plus with ClO//2 has been investigated in aqueous solution at 25. 0 degree C and at an ionic strength of 0. 10 M (NaCF//3SO//3). The equilibrium quotient for formation of left bracket Fe(phen)//3 right bracket **3** plus and CO//2** minus was determined spectrophotometrically to be (1. 98 plus or minus 0. 22) multiplied by 10** minus **3. Since the product ClO//2** minus is a weak base, it was possible by mass action to drive the reaction in the uphill direction in acidic media. In the reverse direction the kinetics were immeasurably rapid, but in the uphill direction the kinetics were slow enough to be measured by using a stopped-flow spectrophotometer. The kinetics were consistent with a mechanism involving reversible bimolecular electron transfer followed by protonation fo the ClO//2** minus . The rate constant for electron transfer was calculated as 4. 5 multiplied by 10**4 M** minus **1 s** minus **1. Applying the cross relationship of Marcus theory leads to an effective self-exchange rate constant of 7. 8 multiplied by 10**1 M** minus **1 s** minus **1 for the ClO//2/ClO//2** minus couple.
- Lednicky,Stanbury
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- Chlorine dioxide reduction by aqueous iron(II) through outer-sphere and inner-sphere electron-transfer pathways
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The reduction of ClO2 to ClO2- by aqueous iron(II) in 0.5 M HClO4 proceeds by both outer-sphere (86%) and inner-sphere (14%) electron-transfer pathways. The second-order rate constant for the outer-sphere reacti
- Wang, Lu,Odeh, Ihab N.,Margerum, Dale W.
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- Dissection of the mechanism of manganese porphyrin-catalyzed chlorine dioxide generation
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Chlorine dioxide, an industrially important biocide and bleach, is produced rapidly and efficiently from chlorite ion in the presence of water-soluble, manganese porphyrins and porphyrazines at neutral pH under mild conditions. The electron-deficient manganese(III) tetra-(N,N-dimethyl)imidazolium porphyrin (MnTDMImP), tetra-(N,N-dimethyl)benzimidazolium (MnTDMBImP) porphyrin, and manganese(III) tetra-N-methyl-2,3-pyridinoporphyrazine (MnTM23PyPz) were found to be the most efficient catalysts for this process. The more typical manganese tetra-4-N-methylpyridiumporphyrin (Mn-4-TMPyP) was much less effective. Rates for the best catalysts were in the range of 0.24-32 TO/s with MnTM23PyPz being the fastest. The kinetics of reactions of the various ClOx species (e.g., chlorite ion, hypochlorous acid, and chlorine dioxide) with authentic oxomanganese(IV) and dioxomanganese(V)MnTDMImP intermediates were studied by stopped-flow spectroscopy. Rate-limiting oxidation of the manganese(III) catalyst by chlorite ion via oxygen atom transfer is proposed to afford a trans-dioxomanganese(V) intermediate. Both trans-dioxomanganese(V)TDMImP and oxoaqua-manganese(IV)TDMImP oxidize chlorite ion by 1-electron, generating the product chlorine dioxide with bimolecular rate constants of 6.30 × 10 3 M-1 s-1 and 3.13 × 103 M-1 s-1, respectively, at pH 6.8. Chlorine dioxide was able to oxidize manganese(III)TDMImP to oxomanganese(IV) at a similar rate, establishing a redox steady-state equilibrium under turnover conditions. Hypochlorous acid (HOCl) produced during turnover was found to rapidly and reversibly react with manganese(III)TDMImP to give dioxoMn(V)TDMImP and chloride ion. The measured equilibrium constant for this reaction (Keq = 2.2 at pH 5.1) afforded a value for the oxoMn(V)/Mn(III) redox couple under catalytic conditions (E′ = 1.35 V vs NHE). In subsequent processes, chlorine dioxide reacts with both oxomanganese(V) and oxomanganese(IV)TDMImP to afford chlorate ion. Kinetic simulations of the proposed mechanism using experimentally measured rate constants were in agreement with observed chlorine dioxide growth and decay curves, measured chlorate yields, and the oxoMn(IV)/Mn(III) redox potential (1.03 V vs NHE). This acid-free catalysis could form the basis for a new process to make ClO2.
- Umile, Thomas P.,Wang, Dong,Groves, John T.
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p. 10353 - 10362
(2011/11/29)
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- Nucleophile Assistance of Electron-Transfer Reactions between Nitrogen Dioxide and Chlorine Dioxide Concurrent with the Nitrogen Dioxide Disproportionation
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The reaction of chlorine dioxide with excess NO2- to form ClO2- and NO3- in the presence of a large concentration of ClO2- is followed via stopped-flow spectroscopy. Concentrations are set to establish a preequilibrium among ClO2, NO2-, ClO2-, and an intermediate, NO2. Studies are conducted at pH 12.0 to avoid complications due to the ClO2-/NO2- reaction. These conditions enable the kinetic study of the ClO2 reaction with nitrogen dioxide as well as the NO2 disproportionation reaction. The rate of the NO2/ClO2 electron-transfer reaction is accelerated by different nucleophiles (NO2- > Br- > OH- > CO32- > PO43- > ClO2- > H 2O). The third-order rate constants for the nucleophile-assisted reactions between NO2 and ClO2 (kNu, M -2 s-1) at 25.0 °C vary from 4.4 × 10 6 for NO2- to 2.0 × 103 when H2O is the nucleophile. The nucleophile is found to associate with NO2 and not with ClO2 in the rate-determining step to give NuNO2+ + ClO2-. The concurrent NO2 disproportionation reaction exhibits no nucleophilic effect and has a rate constant of 4.8 × 107 M-1 s -1. The ClO2/NO2/nucleophile reaction is another example of a system that exhibits general nucleophilic acceleration of electron transfer. This system also represents an alternative way to study the rate of NO2 disproportionation.
- Becker, Robert H.,Nicoson, Jeffrey S.,Margerum, Dale W.
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p. 7938 - 7944
(2008/10/09)
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- New pathways for chlorine dioxide decomposition in basic solution
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The product distribution from the decay of chlorine dioxide in basic solution changes as the ClO2 concentration decreases. While disproportionation reactions that give equal amounts of ClO2- and ClO3- dominate the stoichiometry at millimolar or higher levels of ClO2, the ratio of ClO2- to ClO3- formed increases significantly at micromolar ClO2 levels. Kinetic evidence shows three concurrent pathways that all exhibit a first-order dependence in [OH-] but have variable order in [ClO2]. Pathway 1 is a disproportionation reaction that is first order in [ClO2]. Pathway 2, a previously unknown reaction, is also first order in [ClO2] but forms ClO2- as the only chlorine-containing product. Pathway 3 is second order in [ClO2] and generates equal amounts of ClO2- and ClO3-. A Cl2O4 intermediate is proposed for this path. At high concentrations of ClO2, pathway 3 causes the overall ClO3- yield to approach the overall yield of ClO2-. Pathway 2 is attributed to OH- attack on an oxygen atom of ClO2 that leads to peroxide intermediates and yields ClO2- and O2 as products. This pathway is important at low levels of ClO2.
- Odeh, Ihab N.,Francisco, Joseph S.,Margerum, Dale W.
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p. 6500 - 6506
(2008/10/08)
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- Bromite ion catalysis of the disproportionation of chlorine dioxide with nucleophile assistance of electron-transfer reactions between ClO2 and BrO2 in basic solution
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The rate of ClO2 conversion to ClO2- and ClO3- is accelerated by BrO2-, repressed by ClO2-, and greatly assisted by many nucleophiles (Br- > PO43- > HPO42- > CO32- > Cl- ~ OH- > CH3COO- ~ SO42- C5H5N ? H2O). The kinetics (at p[H+] = 9.3-12.9) show that the first step of the mechanism is an electron transfer between ClO2 and BrO2- (k1 = 36 M-1 s-1) to give ClO2- and BrO2. This highly reversible reaction (k1/k-1 = 1 × 10-6) accounts for the observed inhibition by ClO2-. The second step is an electron transfer between ClO2 and BrO2 to regenerate BrO2- and form ClO3-. A novel aspect of the second step is the large kinetic contribution from nucleophiles (kNu) that assist the electron transfer between ClO2 and BrO2. The kNu (M-2 s-1) values at 25.0 °C vary from 2.89 × 108 for Br- to 2.0 × 104 for H2O.
- Wang, Lu,Nicoson, Jeffrey S.,Huff Hartz, Kara E.,Francisco, Joseph S.,Margerum, Dale W.
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p. 108 - 113
(2008/10/08)
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- Hypohalite ion catalysis of the disproportionation of chlorine dioxide
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The disproportionation of chlorine dioxide in basic solution to give ClO2- and ClO3- is catalyzed by OBr- and OCl-. The reactions have a first-order dependence in both [ClO2] and [OX-] (X = Br, Cl) when the ClO2- concentrations are low. However, the reactions become second-order in [ClO2] with the addition of excess ClO2-, and the observed rates become inversely proportional to [ClO2-]. In the proposed mechanisms, electron transfer from OX- to ClO2 (k1OBr- = 2.05 ± 0.03 M-1 s-1 for OBr-/ClO2 and k1OCl- = 0.91 ± 0.04 M-1 s-1 for OCl-/ClO2) occurs in the first step to give OX and ClO2-. This reversible step (k1OBr-/k-1OBr- = 1.3 × 10-7 for OBr-/ClO2, k1OCl-/k-1OCl = 5.1 × 10-10 for OCl-/ClO2) accounts for the observed suppression by ClO2-. The second step is the reaction between two free radicals (XO and ClO2) to form XOClO2. These rate constants are k2OBr = 1.0 × 108 M-1 s-1 for OBr/ClO2 and k2OCl = 7 × 109 M-1 s-1 for OCl/ClO2. The XOClO2 adduct hydrolyzes rapidly in the basic solution to give ClO3- and to regenerate OX-. The activation parameters for the first step are ΔH1? = 55 ± 1 kJ mol-1, ΔS1? = - 49 ± 2 J mol-1 K-1 for the OBr-/ClO2 reaction and ΔH1? = 61 ± 3 kJ mol-1, ΔS1? = - 43 ± 2 J mol-1 K-1 for the OCl-/ClO2 reaction.
- Wang, Lu,Margerum, Dale W.
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p. 6099 - 6105
(2008/10/08)
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- Kinetics and mechanism of catalytic decomposition and oxidation of chlorine dioxide by the hypochlorite ion
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The oxidation of ClO2 by OCl-is first order with respect to both reactants in the neutral to alkaline pH range: -d[ClO2]/dt = 2kOCl[ClO2][OCl-]. The rate constant (T = 298 K, μ = 1.0 M NaCl
- Csordas,Bubnis,Fabian,Gordon
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p. 1833 - 1836
(2008/10/08)
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- Oxidation of peroxynitrite by inorganic radicals: A pulse radiolysis study
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Reactivity of the peroxynitrite ion toward a number of inorganic radicals was determined by using the pulse radiolysis technique. The rate constants for the oxidation of the ONOO- ion by CO3·-, ·N3, and ClO2· radicals were determined from their decay kinetics to be (7.7 ± 1.2) x 106 (I = 0.6 M), (7.2 ± 0.9) x 108, and (3.2 ± 0.3) x 104 M-1 s-(l), respectively. For the ·OH radical, the rate constant of (4.8 ± 0.8) x 109 M-1 s-1 was obtained by using competition kinetic analysis. The oxidation potential of the ONOO- ion was estimated as 0.8 V from the kinetic data. Although thermodynamically favorable, oxidation of ONOO- by the °NO2 radical was not observed; an upper limit of 2.5 x 104 M-1 s-1 could be set for this reaction. Contribution from some of these reactions to the decomposition of peroxynitrite in the presence and absence of CO2 is discussed.
- Goldstein, Sara,Saha, Abhijit,Lymar, Sergei V.,Czapski, Gidon
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p. 5549 - 5554
(2007/10/03)
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- Kinetics and mechanism of the reaction between thiosulfate and chlorine dioxide
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The reaction between thiosulfate and chlorine dioxide in slightly alkaline medium has been studied by stopped- flow techniques. The reaction cannot be studied under pseudo-first-order condition, thus a new approach based on the improved calibration and use of stopped-flow spectrophotometers was applied. The reaction starts with irreversible formation of ?S2O3ClO22- radical. The main path of the reaction produces tetrathionate and chlorite through the formation of light absorbing tetrathionate radical (?S4O63-). Any of the reactant present in excess slightly modifies the 1:1 stoichiometry, and sulfate as well as chloride ions are also formed. A detailed mechanism based on a rigorous simultaneous fitting of the experimental data is proposed.
- Horvath, Attila K.,Nagypal, Istvan
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p. 7267 - 7272
(2007/10/03)
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- The Kinetics and Mechanism of the Chlorine Dioxide - Iodide Ion Reaction
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The oxidation of iodide ion by chlorine dioxide has been studied by stopped-flow techniques at I = 1.0 M (NaClO4). The following two-term rate law was confirmed for the reaction: -d[ClO2]/dt = kI[ClO2][I-/
- Fábián, István,Gordon, Gilbert
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p. 2494 - 2497
(2008/10/09)
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- Oxygen-Transfer Reactions of Methylrhenium Oxides
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Methylrhenium dioxide, CH3ReO2 (or MDO), is produced from methylrhenium trioxide, CH3ReO3 (or MTO), and hypophosphorous acid in acidic aqueous medium. Its mechanism is discussed in light of MTO's coordination ability and the inverse kinetic isotope effect (kie): H2P(O)OH, k = 0.028 L mol-1 s-1; D2P(O)OH, k = 0.039 L mol-1 s-1. The Re(V) complex, MDO, reduces perchlorate and other inorganic oxoanions (XOn-, where X = Cl, Br, or I and n = 4 or 3). The rate is controlled by the first oxygen abstraction from perchlorate to give chlorate, with a second-order rate constant at pH 0 and 25°C of 7.3 L mol-1 s-1. Organic oxygen-donors such as sulfoxides and pyridine N-oxides oxidize MDO to MTO as do metal oxo complexes: V(aq)2+, VO2+(aq), HOMoO2+(aq), and MnO4-. The reaction between V(aq)2+ with MTO and the reduction of VO2+ with MDO made it possible to determine the free energy for MDO/MTO. Oxygen-atom transfer from oxygen-donors to MDO involves nucleophilic attack of X-O on the electrophilic Re(V) center of MDO; the reaction proceeds via an [MDO-XO] adduct, which is supported by the saturation kinetics observed for some. The parameters that control and facilitate the kinetics of such oxygen-transfer processes are suggested and include the force constant for the asymmetric stretching of the element-oxygen bond.
- Abu-Omar, Mahdi M.,Appelman, Evan H.,Espenson, James H.
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p. 7751 - 7757
(2008/10/09)
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- Electron transfer between azide and chlorine dioxide: The effect of solvent barrier nonadditivity
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The reaction of chlorine dioxide with excess azide in aqueous media proceeds with complex kinetics and produces N2, N2O, NO3-, Cl-, and ClO2-. In the presence of the spin trap PBN, the reaction is much simpler, and the rate law is -d [ClO2]/dt = k1 [ClO2] [N3-] [PBN]/([PBN] + [ClO2-]k-1/k2), with k1 = 809 M-1 s-1 and k-1/k2 = 19.0 at 25 °C. The inferred mechanism implies that k1 is the rate constant of electron transfer between ClO2 and N3-, k-1 is the reverse rate constant (N3 with ClO2-), and k2 is the rate constant for reaction of N3 with PBN. A dramatically lower value for k1 of 0.62 M-1 s-1 is calculated from the Marcus cross relationship and literature values for the self-exchange rates. The discrepancy is attributed to systematic errors in the literature self-exchange rates that were derived by applying the Marcus cross relationship to reactions of coordination complexes with N3- and ClO2. Such errors develop whenever this method is applied to reactions between species of widely differing size. Correcting for this effect leads to a calculated value of 56 M-1 s-1 for k1, which is in much improved agreement with the observed value. Similar corrections lead to greatly improved correlations for the self-exchange reaction of NO2 with NO2- and the electrontransfer reaction of ClO2 with NO2-.
- Awad,Stanbury
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p. 3636 - 3642
(2007/10/02)
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- The Primary Process ClO3- (+hν) ClO- + O2 in the Photolysis of Aqueous ClO3- Solutions
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The quantum yield, Φ1, in the primary process ClO3- (+hν) ClO- + O2 (1) and the sum of the quantum yields Φ1 + Φ2 in the primary processes ClO3- (+hν) ClO2 + O- (2) and ClO3- ClO2- + O(3P) (3) were measured in the steady state photolysis of aqueous ClO3- solutions at 214 and 229 nm.The ratio of the yields of ClO- and ClO3- in the reactions ClO2 ClO- + O2 and ClO2 + O- ClO3- (4) was determined by γ-radiolysis of aqueous solutions of ClO2 at varying pH.The finding that the ratio between the yields of ClO- and ClO3- in reactions 4 equals the ratio between Φ1 and the quantum yield, Φ0 = 1 -Φ1 - Φ2 - Φ3, for ClO3- returning to the ground state is taken as evidence that process 1 results from a cage-back reaction.This result combined with recent studies of the radiolysis of KClO3 crystals suggest that the primary processes in the photolysis of aqueous ClO3- originate in a common process by which O- is expelled from ClO3- upon photoexcitation.The expelled O- may escape the solvent cage containing ClO2 (process 2), or react in cage-back reaction (process 0 and 1).During the expulsion of O- the photoproducts may convert to ClO2- and O(3P) (process 3).
- Klaening, U. K.,Sehested, K.
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p. 740 - 743
(2007/10/02)
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- The one-electron reduction potential of 4-substituted phenoxyl radicals in water
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By means of pulse radiolysis the one-electron reduction potentials of twelve 4-substituted phenoxy radicals have been determined. The main reference used was the ClO2./ClO2- couple. By combining the redox potentials of phenoxyl radicals with the aqueous acidities of phenols the bond strength of the phenolic O-H bond was calculated. These values were found to be in good agreement with O-H bond dissociation enthalpies measured in the gas phase.
- Lind,Shen,Eriksen,Merényi
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p. 479 - 482
(2007/10/02)
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- MASS-SPECTROMETRIC AND QUANTUM-CHEMICAL INVESTIGATION OF THERMOCHEMICAL CHARACTERISTICS OF CHLORINE OXIDES
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An electron impact technique has been used for the direct determination of the ionization potential (IP) of the ClO3 radical and the electron affinity (EA) of the ClO3 and ClO4 radicals.By means of quantum-chemical calculations taking into account configu
- Alekseev, V. I.,Zyubina, T. S.,Zyubin, A. S.,Baluev, A. V.
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p. 2092 - 2096
(2007/10/02)
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- Electron Transfer From Indoles, Phenol, and Sulfite (SO32-) to Chlorine Dioxide (ClO2.)
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With the ClO2/ClO2- couple as reference the one-electron-reduction potentials have been determined for four methylated indolyl radical cations.Their Eo values are 1.23 V (N-Me), 1.10 V (2-Me), 1.07 V (3-Me), and 0.93 V (2,3-diMe).Eo values were also measured for the following: tryptophylH.+/trypH 1.24 V, SO3.-/SO32- 0.76 V, and phenoxy./phenolate 0.80 V.The redox potentials were obtained from purely kinetic data (for tryptophan and 2-, 3-, and N-methylindole) or from combined kinetic and thermodynamic measurements.
- Merenyi, Gabor,Lind, Johan,Shen, Xinhua
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p. 134 - 137
(2007/10/02)
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- Solvent effect on the rate of N(III)/Cl(V) reaction
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Kinetics of the reaction between N(III) and Cl(V) have been studied in water and water-dioxan solutions.The rate equation of the reaction in each solvent could be written as Rate=k3->+> and the rate rises as the dielectric constant of the medium is lowered.This observation is in accord with suggested mechanistic details involving the intermediate H2NClO5.
- Emeish, Samir S.
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p. 902 - 905
(2007/10/02)
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