Using [H2O2] in the molar range, the reaction with Fe2+ has two phases: in the first rapid phase, only a small fraction of the total O2 is evolved; the bulk of the gas is formed in a slow second phase. In interpretations based on the free radical model of Barb et al., the first phase has been identified with the ‘Fenton reaction’ (reaction of Fe2+with H2O2), while the second with catalytic decomposition of H2O2 by Fe3+ ions. This interpretation is not correct. A new analysis of the model shows that (1) it is a chain reaction having no termination steps and (2) the ‘Fenton part’ alone consists of two phases. It starts with rapid evolution of O2 via a five-membered chain reaction (first phase). When [Fe2+] becomes low, evolution of O2 continues in a three-membered chain reaction at a greatly reduced rate (second phase). In later stages of the second phase, Fe3+ catalysis contributes to O2 evolution. Thus, the amount of O2 formed in the rapid phase cannot be identified with the total amount formed in the ‘Fenton reaction’ but only with that formed in its first phase. Computer simulations of O2 evolution based on the model of Barb et al. and rate constants show a definite dependence of this quantity on the initial [H2O2] – in contrast to the experimentally found independence. More satisfactory, but not complete, agreement with measured data could be reached in simulations using a non-radical model. Some of the difficulty has been due to the determination of the exact position of the end of the first phase. The transition between the two phases of the reaction occurs in a short, but finite time interval. It has been shown that the quantity ‘total amount of O2 evolved in the Fenton reaction’ (subtracting the part due to Fe3+catalysis) is not accessible to experimental determination nor to theoretical calculation.

中文翻译：

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芬顿反应的新动力学分析：自由基链式反应概念的批判性检验

使用摩尔范围内的 [H2O2]，与 Fe2+ 的反应有两个阶段：在第一个快速阶段，仅释放出总 O2 的一小部分；大部分气体在缓慢的第二阶段形成。在基于 Barb 等人的自由基模型的解释中，第一阶段已被确定为“芬顿反应”（Fe2+与 H2O2 的反应），而第二阶段与 Fe3+ 离子催化分解 H2O2。这种解释是不正确的。对模型的新分析表明 (1) 它是一个没有终止步骤的链式反应，(2) 单独的“芬顿部分”由两个阶段组成。它始于 O2 通过五元链式反应（第一阶段）的快速演变。当 [Fe2+] 变低时，O2 以大大降低的速率（第二阶段）在三元链式反应中继续释放。在第二阶段的后期阶段，Fe3+ 催化有助于 O2 析出。因此，快速相中形成的 O2 量不能与“芬顿反应”中形成的总量相鉴别，而只能与第一相中形成的 O2 量相鉴别。基于 Barb 等人模型的 O2 演化的计算机模拟。和速率常数显示该数量对初始 [H2O2] 的明确依赖性 - 与实验发现的独立性相反。在使用非根本模型的模拟中可以与测量数据达成更令人满意但不完全的一致。一些困难是由于确定第一阶段结束的确切位置。反应的两个阶段之间的转变发生在很短但有限的时间间隔内。