PROTON-INDUCED DISPROPORTIONATION OF SUPEROXIDE ION IN APROTIC MEDIA
PROTON-INDUCED DISPROPORTIONATION OF SUPEROXIDE ION IN APROTIC MEDIA
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DOI：
10.1021/ja00369a025
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发表时间：
1982-01-01
影响因子：
15
通讯作者：
SAWYER, DT
中科院分区：
文献类型：
--
作者：
CHIN, DH;CHIERICATO, G;SAWYER, DT
通过停流分光光度法、循环伏安法和转盘电极上的控制电位伏安法研究了二甲基甲酰胺和乙腈中质子诱导的超氧离子 (Of) 歧化。对于强酸性底物（HC104、HCl 和 NH4C104），歧化反应相对于 Of 是二阶反应，但速度太快而无法准确测量，k> 107 M'1 s'1。对于质子较少的底物（抗坏血酸、酚类、儿茶酚、醇和水），歧化速率相对于 Of 和底物而言是一阶的；质子转移是限速步骤。在二甲基甲酰胺中，二阶速率常数范围从抗坏血酸的 k= 2 X 104 M" 1 s" 1 到水的 k= 1 X 10'3。在动力学数据的基础上，提出了非水溶剂中酸性底物超氧化物歧化的自洽机制。通过脉冲辐射解详细表征了水介质中超氧化物（Of）的水解和歧化动力学。 1'5 对于所有条件，限速步骤是浓度的二阶。最大速率发生在 pH 值等于 H02· 的 pXa 时；随着氢离子浓度的进一步降低，它单调降低。
The proton-induced disproportionation of superoxide ion (Of) in dimethylformamide and in acetonitrile has been studied by stopped-flow spectrophotometry, cyclic voltammetry, and controlled-potential voltammetry at a rotating-disk electrode. For strongly acidic substrates (HC104, HC1, and NH4C104) the disproprotionation reaction is second order with respect to Of, but too rapid to measure accurately, k> 107 M'1 s'1. With less protic substrates (ascorbic acid, phenols, catechols, alcohols, and water) the rate of disproportionation is first order with respect to Of and with respect to substrate; proton transfer is the rate-limiting step. In dimethylformamide the second-order rate constants range from k= 2 X 104 M" 1 s" 1 for ascorbic acid to k= 1 X 10'3 for water. On the basis of the kinetic data, a self-consistent mechanism for superoxide disproportionation by acidic substrates in nonaqueous solvents is proposed.The dynamics for the hydrolysis and disproportionation of superoxide (Of) in aqueous media havebeen characterized in detail by pulse radiolysis. 1'5 For all conditions, the rate-limiting step is second order in Of concentration. The maximum rate occurs at a pH that is equivalent to the pXa for H02·; it decreases monotonically with further decreases in the hydrogen ion con-centration.