Iron-mediated oxidation of methoxyhydroquinone at the Rifle Floodplain, Colorado

In this study, the oxidation of 2-methoxyhydroquinone (MH2Q) by ferric iron (Fe(III)) under dark conditions in the absence and presence of oxygen was investigated within a pH range of 4 – 6. While Fe(III) was capable of stoichiometrically oxidizing MH2Q under anaerobic conditions, catalytic oxidation of MH2Q was observed in the presence of O2 due to further cycling between oxygen, semiquinone radicals, and iron species. A detailed kinetic model was developed to describe the predominant mechanisms, which indicated that both the undissociated and mono-dissociated anions of MH2Q were kinetically active species towards Fe(III) reduction, with the mono-dissociated anion being the key species accounting for the pH dependence of the oxidation. The generated radical intermediates, namely semiquinone and superoxide, are of great importance in reaction chain propagation. The kinetic model may provide critical insight into the underlying mechanisms of the thermodynamic and kinetic characteristics of metal-organic interactions and assist in understanding and predicting the factors controlling iron and organic matter transformation and bioavailability in aquatic systems.本研究在pH 4~6的范围内，探究了避光条件下，无氧与有氧体系中三价铁(Fe(III))对2-甲氧基对苯二酚(2-methoxyhydroquinone, MH2Q)的氧化反应。研究发现，厌氧条件下三价铁可通过化学计量方式氧化MH2Q；而在有氧条件下，由于氧气、半醌自由基与铁物种之间发生进一步的循环反应，MH2Q被催化氧化。本研究构建了详细的动力学模型以阐释主导反应机制，结果表明，MH2Q的未解离态与单解离态阴离子均为参与三价铁还原过程的动力学活性物种，其中单解离态阴离子是决定该氧化反应pH依赖性的关键物种。生成的自由基中间体——半醌与超氧自由基——在反应链传递过程中发挥重要作用。该动力学模型可为金属-有机相互作用的热力学与动力学特性的内在机制提供关键见解，有助于理解并预测水生系统中铁与有机物转化及生物有效性的调控因素。