Bossmann S H, Oliveros E, Kantor M, Niebler S, Bonfill A, Shahin N, Wörner M, Braun A M
Lehrstuhl für Umweltmesstechnik am Engler-Bunte Institut der Universität Karlsruhe, Engler-Bunte-Ring 1, Postfach 6980, D-76128 Karlsruhe, Germany.
Water Sci Technol. 2004;49(4):75-80.
Although the Fenton reagent (a mixture of hydrogen peroxide and an iron(II) salt) has been known for more than a century, the manifold mechanisms occurring during the thermal Fenton reaction are still under discussion. Indeed, this discussion served as a powerful driving force for the steadily increasing insight into the field of inorganic radical and electron transfer chemistry. In this work, an experimental approach towards the elucidation of the first steps taking place in the reaction between several iron(II)-complexes and hydrogen peroxide (H2O2) in water at pH = 3.0 is presented. 2,4-xylidine (2,4-dimethylaniline) reacts differently with reactive intermediates via the addition or hydrogen abstraction by the hydroxyl radical (HO*) or electron transfer reactions to higher valent iron-species, such as a hydrated ferryl-complex (Fe(IV)). The chemical reactivity of the employed iron(II)-complexes with H2O2 differed strongly depending on their ground-state one-electron oxidation potentials. The results are interpreted in accordance with the paradigm originally developed by Goldstein et al. which is based on the evidence obtained from the Marcus theory that outer-sphere electron transfer reactions between metal complexes are not likely to occur because they are too slow. Therefore, most of the "Fenton-reagents" form transient metal complexes, which can be described as [LnFe-H2O2]m+. They form, depending on the reaction conditions, either the hydroxyl radical or higher-valent iron complex species.
尽管芬顿试剂（过氧化氢与亚铁盐的混合物）已为人所知达一个多世纪之久，但热芬顿反应过程中发生的多种机制仍在讨论之中。事实上，这一讨论成为了不断深入了解无机自由基和电子转移化学领域的强大驱动力。在这项工作中，我们展示了一种实验方法，用于阐明在pH = 3.0的水中，几种亚铁络合物与过氧化氢（H₂O₂）反应时发生的初始步骤。2,4 - 二甲基苯胺（2,4 - 二甲苯胺）通过羟基自由基（HO*）的加成或氢提取，或者通过电子转移反应与更高价态的铁物种（如水合铁酰络合物（Fe(IV)））反应，与反应中间体的反应方式不同。所使用的亚铁络合物与H₂O₂的化学反应活性因其基态单电子氧化电位的不同而有很大差异。这些结果是根据戈尔茨坦等人最初提出的范式进行解释的，该范式基于从马库斯理论获得的证据，即金属络合物之间的外层电子转移反应不太可能发生，因为它们太慢了。因此，大多数“芬顿试剂”会形成瞬态金属络合物，可描述为[LnFe - H₂O₂]m⁺。根据反应条件，它们会形成羟基自由基或更高价态的铁络合物物种。
