Abstract

The work presents an approach for studying the kinetics, mechanism, and reactivity of intermediates of a wide class of redox reactions for which the rate-limiting step is the redox decomposition of the intermediate complex. The approach was applied to the investigation of the oxidation of oxalic acid (H₂Ox) by cerium(IV) in a sulfuric acid medium as part of the Belousov–Zhabotinsky oscillating reaction (BZ reaction) catalyzed by cerium ions. Experimental, mathematical, and computational methods that are typically used to study metal complexes in a stable oxidation state were kinetically generalized to variable-valence metal complexes and were used to determine the characteristics of intermediate complexes of the cerium(IV)–oxalate reaction and derive a general equation for its rate based on a set of equations describing the rapid achievement of pre-equilibrium in the system and the subsequent nonequilibrium process. A quantitative model of the process was proposed; it included two parallel reaction pathways, for which two different cerium(IV)–oxalate intermediate complexes were identified and characterized. The complexes have similar reactivity, which may be due to the similarity of the structure of their inner coordination spheres and the inner-sphere mechanism of electron transfer in the complexes. Using the developed model, a diagram of the yields of all main species of cerium(IV) under the conditions of the BZ reaction was constructed, which indicates the need to take into account the formation of intermediate complexes of the composition CeOHOx\(_{n}^{{3 - 2n}}\) (n = 1, 2) in the oxidation of oxalic acid under these conditions. The main difference between the presented model of the cerium(IV)–oxalate reaction as part of the BZ reaction and the previous models is the explicit consideration of the participation of intermediate complexes of cerium(IV) with oxalic acid anions and sulfate background anions in the reaction.

中文翻译：

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硫酸盐介质中铈(IV)-草酸盐反应中间体的动力学、机理和反应性

摘要

这项工作提出了一种研究多种氧化还原反应中间体的动力学、机理和反应性的方法，其中限速步骤是中间体配合物的氧化还原分解。该方法应用于研究硫酸介质中铈(IV)氧化草酸(H _{2 Ox)，作为铈离子催化的Belousov-Zhabotinsky 振荡反应（BZ 反应）的一部分。}通常用于研究稳定氧化态金属配合物的实验、数学和计算方法在动力学上推广到变价金属配合物，并用于确定铈（IV）-草酸盐反应的中间配合物的特征并推导其速率的一般方程基于描述系统中快速实现预平衡和随后的非平衡过程的一组方程。提出了该过程的定量模型；它包括两个平行的反应途径，其中两种不同的铈（IV）-草酸盐中间配合物被鉴定和表征。配合物具有相似的反应活性，这可能是由于配合物内配位层结构和内层电子转移机制的相似性。使用开发的模型，构建了 BZ 反应条件下所有主要铈（IV）物质的产率图，这表明需要考虑组成 CeOHO x \(_ {n}^{{3 - 2n}}\) ( n = 1, 2) 在这些条件下草酸的氧化。作为BZ反应一部分的铈(IV)-草酸盐反应模型与之前的模型之间的主要区别在于明确考虑了铈(IV)与草酸阴离子和硫酸根背景阴离子的中间配合物的参与的反应。