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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >One-Electron Oxidation and Reduction of Different Tautomeric Forms of Azo Dyes: A Pulse Radiolysis Study
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One-Electron Oxidation and Reduction of Different Tautomeric Forms of Azo Dyes: A Pulse Radiolysis Study

机译：单电子氧化和还原不同互变异构形式的偶氮染料：脉冲辐解研究

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摘要

To characterize the relative reactivities of different dye tautomeric forms of model azo dyes, pulse radiolysis studies were made of their reactions with either oxidizing radicals (hydroxyl radical (~·OH) and N_3~·) or reducing species (e_(aq)~- and the 2-hydroxy-2-propyl radical) in the pH range 3-12. Methyl organe, 2-(arylazo)-1-naphthol-3,6-disulfonate, and orange I or its O-methylated derivative undergo direct one-electron oxidation with N_3~· and one-electron reduction with either e_(aq)~- or the 2-hydroxy-2-propyl radical. The efficiency of one-electron oxidation of the dyes is strongly dependent upon their different tautomeric forms in the order common ion > hydrazone > azo. In contrast, the ease of reduction of the different tautomeric forms of the dyes is in the order protonated azo ≥ hydrazone > azo > common ion but shows a weaker dependence than that seen for oxidation. Radical intermediates formed either from one-electron oxidation or from one-electron reduction of the dyes mainly decay bimolecularly to give product(s) through radical-radical disproportionation. The reactivity of the ~·OH adducts that decay bimolecularly to give addition product(s) by radical-radical combination (dimerization) at high radical concentrations. However, intermediates formed from orange I and its O-methylated derivative exhibit a competing hydroxyl ion elimination to give the one-electron-oxidized species, which decay by disproportionation, a less efficient process than bimolecular dimerization. Thus, the efficiency of removal of the dye by the ~·OH is critically dependent on the pH, which governs the competition between the bimolecular dimerization of the ~·OH adducts and the first-order water elimination pathway.
机译：为了表征偶氮染料模型的不同染料互变异构形式的相对反应性，对它们与氧化自由基（羟基自由基（〜·OH）和N_3〜·）或还原物种（e_（aq）〜-和2-羟基-2-丙基）的pH范围为3-12。甲基有机物，2-（芳基偶氮）-1-萘酚-3,6-二磺酸盐和橙I或其O-甲基化衍生物通过N_3〜直接进行单电子氧化并通过e_（aq）〜进行单电子还原-或2-羟基-2-丙基。染料的单电子氧化效率在很大程度上取决于它们的不同互变异构形式，顺序为普通离子>偶氮。相反，还原不同互变异构形式的染料的难易程度是：质子化的偶氮≥>偶氮>普通离子，但显示出比氧化弱的依赖性。由染料的单电子氧化或单电子还原形成的自由基中间体主要通过自由基自由基歧化而双分子降解以产生产物。 〜·OH加成物的反应性在高自由基浓度下通过自由基-自由基结合（二聚）双分子分解生成加成产物。但是，由橙I及其O-甲基化衍生物形成的中间体表现出竞争性的氢氧离子消除作用，从而产生单电子氧化物种，该物种由于歧化作用而降解，该过程比双分子二聚作用低效。因此，〜OH去除染料的效率主要取决于pH值，pH决定了〜OH加合物的双分子二聚化和一级除水途径之间的竞争。

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