Electron transfer between azide and chlorine dioxide: the effect of solvent barrier nonadditivity

Awad, Hani H.; Stanbury, David M.

doi:10.1021/ja00062a030

Cited by 22 publications

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“…Due to the protolytic equilibrium 10 between chlorite ion and chlorous acid (p K a = 1.72) the redox potential for the ClO 2 /ClO 2 - couple is pH dependent . However, in slightly acidic to neutral (pH > 4.0) solutions the dominant species is ClO 2 - and the redox potential is invariably E ° = 0.936 V. The self-exchange rate constant for the same couple was reported recently, k 11 = (2.6−6.7) × 10 4 M -1 s -1 (average: 3.3 × 10 4 M -1 s -1 ).…”

Section: Resultssupporting

confidence: 60%

The Kinetics and Mechanism of the Chlorine Dioxide−Iodide Ion Reaction

Fábián

Gordon

1997

Inorg. Chem.

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The oxidation of iodide ion by chlorine dioxide has been studied by stopped-flow techniques at I ) 1.0 M (NaClO 4 ). The following two-term rate law was confirmed for the reaction:The rate constants at 298 K and the activation parameters are k I ) (1.87 ( 0.02) × 10 3 M -1 s -1 , ∆H I q ) 35.4 ( 0.7 kJ/mol, ∆S I q ) -63.5 ( 2.3 J/(mol K), k II ) (1.25 ( 0.04) × 10 4 M -2 s -1 , ∆H II q ) 36.7 ( 1.3 kJ/mol, ∆S II q ) -43.2 ( 4.6 J/(mol K). Both the second-and third-order paths are interpreted in terms of an outersphere electron-transfer mechanism. The calculations based on the Marcus theory yield k I ) 1358 M -1 s -1 for the second-order path.

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Section: Resultssupporting

confidence: 60%

The Kinetics and Mechanism of the Chlorine Dioxide−Iodide Ion Reaction

Fábián

Gordon

1997

Inorg. Chem.

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“…Insights into the unique properties of the nitroxyl/NO x cocatalyst combination can be gleaned from the data above as well as previous literature, − and the tandem catalytic cycle in Scheme provides the basis for our analysis. At the electrode, TEMPO + is reduced to TEMPO radical, which may be reoxidized by NO 2 to close the left-hand cycle.…”

Section: Resultsmentioning

confidence: 99%

High-Potential Electrocatalytic O₂Reduction with Nitroxyl/NO_xMediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis

Gerken

Stahl

2015

ACS Cent. Sci.

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Efficient reduction of O2 to water is a central challenge in energy conversion and many aerobic oxidation reactions. Here, we show that the electrochemical oxygen reduction reaction (ORR) can be achieved at high potentials by using soluble organic nitroxyl and nitrogen oxide (NOx) mediators. When used alone, neither organic nitroxyls, such as 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl (TEMPO), nor NOx species, such as sodium nitrite, are effective ORR mediators. The combination of nitroxyl/NOx species, however, mediates sustained O2 reduction with overpotentials as low as 300 mV in acetonitrile containing trifluoroacetic acid. Mechanistic analysis of the coupled redox reactions supports a process in which the nitrogen oxide catalyst drives aerobic oxidation of a nitroxyl mediator to an oxoammonium species, which then is reduced back to the nitroxyl at the cathode. The electrolysis potential is dictated by the oxoammonium/nitroxyl reduction potential. The overpotentials accessible with this ORR system are significantly lower than widely studied molecular metal-macrocycle ORR catalysts and benefit from the mechanism-based specificity for four-electron reduction of oxygen to water mediated by NOx species, together with kinetically efficient reduction of oxidized NOx species by TEMPO and other organic nitroxyls.

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“…This value meets our requirement that k 3 [ClO 2 - ] is much larger than k 3 ∑ k HA [HA]/(1 + ∑ k HA [HA]). A self-exchange rate constant for ClO 2 /ClO 2 - has been evaluated to be 3.3 × 10 4 M -1 s -1 . It seems unlikely that the less favorable electron-transfer reaction would occur rapidly between BrClO 2 and ClO 2 - to give ClO 2 and BrClO 2 - (followed by breakup of BrClO 2 - to Br - and ClO 2 ).…”

Section: Resultsmentioning

confidence: 99%

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion

1998

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The rate of oxidation of ClO(2)(-) by HOBr is first-order in each reactant and is general-acid-assisted in the presence of phosphate or carbonate buffers. The products are ClO(2) and ClO(3)(-), where the relative yield depends on the concentration ratio of ClO(2)(-)/OH(-). The kinetic dependence indicates the presence of a steady-state intermediate, HOBrOClO(-) (or HOBrClO(2)(-)), that undergoes general-acid-assisted reactions to generate a metastable intermediate, BrOClO (or BrClO(2)). This intermediate reacts very rapidly by two competing pathways: in one path ClO(2)(-) reacts to form 2ClO(2) and Br(-), and in the other path OH(-) (or H(2)O) reacts to form ClO(3)(-) and Br(-). Competition between these pathways determines the yield of ClO(2) but does not affect the rate of loss of HOBr. The reactions are followed by the formation of ClO(2) in the presence of excess ClO(2)(-). The rate expression for the loss of HOBr is k(1)[ClO(2)(-)][HOBr] summation operator(k(HA)[HA])/(k(-)(1) + summation operator(k(HA)[HA])), where k(1) (for the formation of the intermediate) is 97 M(-)(1) s(-)(1) and k(HA)/k(-)(1) (M(-)(1)) values, which depend on the acid (HA) strength, are 3.1 x 10(5) for H(3)O(+), 8.3 for H(2)PO(4)(-), and 0.064 for HCO(3)(-) (25.0 degrees C, &mgr; = 1.0 M). Reactions between HOBr and ClO(2)(-) are much faster than those between HOCl and ClO(2)(-).

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Electron transfer between azide and chlorine dioxide: the effect of solvent barrier nonadditivity

Cited by 22 publications

References 0 publications

The Kinetics and Mechanism of the Chlorine Dioxide−Iodide Ion Reaction

The Kinetics and Mechanism of the Chlorine Dioxide−Iodide Ion Reaction

High-Potential Electrocatalytic O₂Reduction with Nitroxyl/NO_xMediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion

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Electron transfer between azide and chlorine dioxide: the effect of solvent barrier nonadditivity

Cited by 22 publications

References 0 publications

The Kinetics and Mechanism of the Chlorine Dioxide−Iodide Ion Reaction

The Kinetics and Mechanism of the Chlorine Dioxide−Iodide Ion Reaction

High-Potential Electrocatalytic O2Reduction with Nitroxyl/NOxMediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion

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High-Potential Electrocatalytic O₂Reduction with Nitroxyl/NO_xMediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis