Becker Robert H, Nicoson Jeffrey S, Margerum Dale W
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA.
Inorg Chem. 2003 Dec 1;42(24):7938-44. doi: 10.1021/ic0347891.
The reaction of chlorine dioxide with excess NO(2)(-) to form ClO(2)(-) and NO(3)(-) in the presence of a large concentration of ClO(2)(-) is followed via stopped-flow spectroscopy. Concentrations are set to establish a preequilibrium among ClO(2), NO(2)(-), ClO(2)(-), and an intermediate, NO(2). Studies are conducted at pH 12.0 to avoid complications due to the ClO(2)(-)/NO(2)(-) reaction. These conditions enable the kinetic study of the ClO(2) reaction with nitrogen dioxide as well as the NO(2) disproportionation reaction. The rate of the NO(2)/ClO(2) electron-transfer reaction is accelerated by different nucleophiles (NO(2)(-) > Br(-) > OH(-) > CO(3)(2-) > PO(4)(3-) > ClO(2)(-) > H(2)O). The third-order rate constants for the nucleophile-assisted reactions between NO(2) and ClO(2) (k(Nu), M(-2) s(-1)) at 25.0 degrees C vary from 4.4 x 10(6) for NO(2-) to 2.0 x 10(3) when H(2)O is the nucleophile. The nucleophile is found to associate with NO(2) and not with ClO(2) in the rate-determining step to give NuNO(2)(+) + ClO(2)(-). The concurrent NO(2) disproportionation reaction exhibits no nucleophilic effect and has a rate constant of 4.8 x 10(7) M(-1) s(-1). The ClO(2)/NO(2)/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 NO(2) disproportionation.
在高浓度二氧化氯（ClO₂⁻）存在的情况下，通过停流光谱法跟踪二氧化氯与过量亚硝酸根离子（NO₂⁻）反应生成亚氯酸根离子（ClO₂⁻）和硝酸根离子（NO₃⁻）的过程。设定各物质浓度以在ClO₂、NO₂⁻、ClO₂⁻和中间体NO₂之间建立预平衡。研究在pH 12.0的条件下进行，以避免ClO₂⁻/NO₂⁻反应带来的复杂性。这些条件使得能够对ClO₂与二氧化氮的反应以及NO₂歧化反应进行动力学研究。不同亲核试剂（NO₂⁻＞Br⁻＞OH⁻＞CO₃²⁻＞PO₄³⁻＞ClO₂⁻＞H₂O）会加速NO₂/ClO₂电子转移反应。25.0℃时，NO₂与ClO₂之间亲核试剂辅助反应的三阶速率常数（k(Nu)，M⁻² s⁻¹）从NO₂⁻的4.4×10⁶变化到以H₂O作为亲核试剂时的2.0×10³。发现亲核试剂在速率决定步骤中与NO₂结合而不与ClO₂结合，生成NuNO₂⁺ + ClO₂⁻。同时发生的NO₂歧化反应没有亲核效应，速率常数为4.8×10⁷ M⁻¹ s⁻¹。ClO₂/NO₂/亲核试剂反应是电子转移呈现一般亲核加速作用的系统的又一个例子。该系统也代表了一种研究NO₂歧化反应速率的替代方法。
