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首页> 外文期刊>Environmental Science & Technology >Redox Interactions of Cr(Ⅵ) and Substituted Phenols: Products and Mechanism
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Redox Interactions of Cr(Ⅵ) and Substituted Phenols: Products and Mechanism

机译：Cr（Ⅵ）与取代酚的氧化还原相互作用：产物与机理

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摘要

The mechanisms of aqueous oxidation-reduction interactions between Cr(Ⅵ) and substituted phenols (RArOH) were characterized by kinetic analysis and determinations of reaction products and intermediates. A rapid, preoxidative equilibrium between HCrO_4~-and RArOH forms chromate ester intermediates, as verified by spectroscopy. The subsequent rate-limiting ester decomposition proceeds via innersphere electron transfer. The overall rate dependence on [H~+] is well accounted for by three parallel redox pathways involving zero, one, and two protons. The two-proton pathway dominates at pH ≤ 2, the single-proton pathway for 2 < pH < 5, and the proton-independent pathway at pH ≥ 5. The parallel reaction rate expression was fitted to data for 4-methyl-, 4-methoxy-, 2,6-dimethoxy-, and 3,4-dimethoxyphenol for pH 1-6. Beside accurately predicting rates for the calibrated conditions, the model predicts a sharp decline in rates at pH ≥ 6. Rates subsequently measured at pH 7 agreed well with those calculated a priori. Such predictions suggestthatthe proposed mechanism is robust and accurate. Rate constants were correlated with Hammett-type substituent parameters. Reaction products indicated both one-and two-electron pathways.
机译：通过动力学分析和反应产物及中间体的测定，表征了Cr（Ⅵ）与取代酚（RArOH）之间水氧化还原反应的机理。经光谱证实，HCrO 4-和RArOH之间的快速，预氧化平衡形成了铬酸酯中间体。随后的限速酯分解通过内层电子转移进行。对[H〜+]的总速率依赖性由涉及零，一和两个质子的三个平行氧化还原途径很好地解释。在pH≤2时，两个质子途径占主导地位；在2 H <5时，单质子途径占主导地位；在pH≥5时，质子非依赖性途径占主导地位。平行反应速率表达式适用于4-甲基-，4 -pH 1-6的-甲氧基-，2,6-二甲氧基-和3,4-二甲氧基苯酚。除了准确预测校准条件的速率外，该模型还预测pH≥6时速率的急剧下降。随后在pH 7时测得的速率与先验计算的速率完全吻合。这样的预测表明所提出的机制是鲁棒且准确的。速率常数与哈米特型取代基参数相关。反应产物指示一电子和二电子途径。

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  • 来源
    《Environmental Science & Technology》 |1995年第8期|p.1933-1943|共11页
  • 作者

    MICHAEL S. ELOVITZ; WILLIAM FISH;

  • 作者单位

    Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH-8600 Duebendorf, Switzerland;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 环境化学;
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