Tóth Zsuzsanna, Fábián István
University of Debrecen, Department of Inorganic and Analytical Chemistry, Debrecen 10, P.O. Box 21, Hungary H-4010.
Inorg Chem. 2004 Apr 19;43(8):2717-23. doi: 10.1021/ic0354318.
The kinetics and mechanism of the chlorine(III)-HOBr reaction were studied by the stopped-flow method under acidic conditions, pH 1.0-3.0, in 1.0 M NaClO(4) and at 25.0 degrees C. The overall redox process occurs in two consecutive steps via the formation of the BrClO(2) intermediate. The electron transfer reactions are coupled with bromine hydrolysis, the formation of the tribromide ion, and the protolytic equilibrium of chlorine(III). On the basis of simultaneous evaluation of the kinetic traces, the following rate constants were obtained for the redox steps: HClO(2) + HOBr right harpoon over left harpoon BrClO(2) + H(2)O, k(3) = (3.34 +/- 0.02) x 10(4) M(-1) s(-1), k(-3) = (3.5 +/- 1.3) x 10(3) s(-1); BrClO(2) + ClO(2)(-)<==>2ClO(2) + Br(-), k(4) = (2.9 +/- 1.0) x 10(7) M(-1) s(-1). The second step was practically irreversible under the conditions applied, and the value of k(-4) could not be determined. The equilibrium constant for the formation of BrClO(2), K(3) = 9.5 M(-1), was calculated from the kinetic results, and it was confirmed that this species is a very powerful oxidant. The redox potential was also estimated for the BrClO(2) + e(-) = Br(-) + ClO(2) reaction: epsilon(0) approximately 1.70 V.
在酸性条件（pH 1.0 - 3.0）、1.0 M高氯酸钠（NaClO₄）溶液以及25.0℃的温度下，采用停流法研究了氯（III）-次溴酸（HOBr）反应的动力学和反应机理。整个氧化还原过程通过形成中间产物溴氯酸（BrClO₂）分两个连续步骤进行。电子转移反应与溴的水解、三溴离子的形成以及氯（III）的质子解离平衡相耦合。基于对动力学曲线的同步评估，得到了氧化还原步骤的以下速率常数：HClO₂ + HOBr ⇌ BrClO₂ + H₂O，k₃ = (3.34 ± 0.02) × 10⁴ M⁻¹ s⁻¹，k⁻₃ = (3.5 ± 1.3) × 10³ s⁻¹；BrClO₂ + ClO₂⁻ ⇌ 2ClO₂ + Br⁻，k₄ = (2.9 ± 1.0) × 10⁷ M⁻¹ s⁻¹。在所应用的条件下，第二步实际上是不可逆的，无法确定k⁻₄的值。根据动力学结果计算出形成BrClO₂的平衡常数K₃ = 9.5 M⁻¹，证实该物种是一种非常强的氧化剂。还估算了BrClO₂ + e⁻ = Br⁻ + ClO₂反应的氧化还原电位：ε⁰约为1.70 V。
