Kinetics and mechanism of the initial phase of the bromine - chlorite ion reaction in aqueous solution

Zsuzsanna Tóth, I. Fábián

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Abstract

The kinetics and mechanism of the chlorine(III)-bromine reaction are studied by the stopped-flow method under acidic conditions in 1.0 M NaClO4 and at 25.0 °C. There are two kinetically well-separated phases in this reaction. A detailed mechanism is proposed for the first phase of the reaction, in which Br2 oxidizes ClO2 - to chlorine dioxide. It is confirmed that the oxidation occurs via competing parallel reaction steps. The autoinhibition observed in the reaction is attributed to a backward shift in the reversible initial step as the oxidation proceeds. On the basis of simultaneous evaluations of the kinetic traces, the following forward rate constants are obtained for the kinetically significant reaction steps: Br2 + ClO2 - = ClO2 + Br2 -, k1 = (1.3 ± 0.2) x 103 M-1 s-1 (k-1 = 1.1 x 109 M-1 s-1); Br2 - + ClO2 - = ClO2 + 2Br-, k2 = (4.0 ± 0.1) x 106 M-1 s -1; Br + ClO2 - = ClO2 + Br-, k8 = (2.3 ± 0.7) x 108 M-1 s-1; HOBr + HClO2 = BrClO2 + H20 (BrClO2 + ClO2 - = Br- + 2ClO2, very fast), k9 = (1.9 ± 0.1) x 105 M-1 s-1. The possible kinetic role of the reactive BrClO2 intermediate is discussed in detail.

Original languageEnglish
Pages (from-to)4608-4614
Number of pages7
JournalInorganic Chemistry
Volume39
Issue number20
DOIs
Publication statusPublished - Oct 2 2000

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Bromine
bromine
Ions
aqueous solutions
Kinetics
kinetics
Oxidation
ions
Chlorine
chlorine
Rate constants
oxidation
dioxides
chlorite
evaluation
shift

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Kinetics and mechanism of the initial phase of the bromine - chlorite ion reaction in aqueous solution. / Tóth, Zsuzsanna; Fábián, I.

In: Inorganic Chemistry, Vol. 39, No. 20, 02.10.2000, p. 4608-4614.

Research output: Contribution to journalArticle

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abstract = "The kinetics and mechanism of the chlorine(III)-bromine reaction are studied by the stopped-flow method under acidic conditions in 1.0 M NaClO4 and at 25.0 °C. There are two kinetically well-separated phases in this reaction. A detailed mechanism is proposed for the first phase of the reaction, in which Br2 oxidizes ClO2 - to chlorine dioxide. It is confirmed that the oxidation occurs via competing parallel reaction steps. The autoinhibition observed in the reaction is attributed to a backward shift in the reversible initial step as the oxidation proceeds. On the basis of simultaneous evaluations of the kinetic traces, the following forward rate constants are obtained for the kinetically significant reaction steps: Br2 + ClO2 - = ClO2 + Br2 -, k1 = (1.3 ± 0.2) x 103 M-1 s-1 (k-1 = 1.1 x 109 M-1 s-1); Br2 - + ClO2 - = ClO2 + 2Br-, k2 = (4.0 ± 0.1) x 106 M-1 s -1; Br + ClO2 - = ClO2 + Br-, k8 = (2.3 ± 0.7) x 108 M-1 s-1; HOBr + HClO2 = BrClO2 + H20 (BrClO2 + ClO2 - = Br- + 2ClO2, very fast), k9 = (1.9 ± 0.1) x 105 M-1 s-1. The possible kinetic role of the reactive BrClO2 intermediate is discussed in detail.",
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N2 - The kinetics and mechanism of the chlorine(III)-bromine reaction are studied by the stopped-flow method under acidic conditions in 1.0 M NaClO4 and at 25.0 °C. There are two kinetically well-separated phases in this reaction. A detailed mechanism is proposed for the first phase of the reaction, in which Br2 oxidizes ClO2 - to chlorine dioxide. It is confirmed that the oxidation occurs via competing parallel reaction steps. The autoinhibition observed in the reaction is attributed to a backward shift in the reversible initial step as the oxidation proceeds. On the basis of simultaneous evaluations of the kinetic traces, the following forward rate constants are obtained for the kinetically significant reaction steps: Br2 + ClO2 - = ClO2 + Br2 -, k1 = (1.3 ± 0.2) x 103 M-1 s-1 (k-1 = 1.1 x 109 M-1 s-1); Br2 - + ClO2 - = ClO2 + 2Br-, k2 = (4.0 ± 0.1) x 106 M-1 s -1; Br + ClO2 - = ClO2 + Br-, k8 = (2.3 ± 0.7) x 108 M-1 s-1; HOBr + HClO2 = BrClO2 + H20 (BrClO2 + ClO2 - = Br- + 2ClO2, very fast), k9 = (1.9 ± 0.1) x 105 M-1 s-1. The possible kinetic role of the reactive BrClO2 intermediate is discussed in detail.

AB - The kinetics and mechanism of the chlorine(III)-bromine reaction are studied by the stopped-flow method under acidic conditions in 1.0 M NaClO4 and at 25.0 °C. There are two kinetically well-separated phases in this reaction. A detailed mechanism is proposed for the first phase of the reaction, in which Br2 oxidizes ClO2 - to chlorine dioxide. It is confirmed that the oxidation occurs via competing parallel reaction steps. The autoinhibition observed in the reaction is attributed to a backward shift in the reversible initial step as the oxidation proceeds. On the basis of simultaneous evaluations of the kinetic traces, the following forward rate constants are obtained for the kinetically significant reaction steps: Br2 + ClO2 - = ClO2 + Br2 -, k1 = (1.3 ± 0.2) x 103 M-1 s-1 (k-1 = 1.1 x 109 M-1 s-1); Br2 - + ClO2 - = ClO2 + 2Br-, k2 = (4.0 ± 0.1) x 106 M-1 s -1; Br + ClO2 - = ClO2 + Br-, k8 = (2.3 ± 0.7) x 108 M-1 s-1; HOBr + HClO2 = BrClO2 + H20 (BrClO2 + ClO2 - = Br- + 2ClO2, very fast), k9 = (1.9 ± 0.1) x 105 M-1 s-1. The possible kinetic role of the reactive BrClO2 intermediate is discussed in detail.

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