Autocatalysis-Driven Clock Reaction III: Clarifying the Kinetics and Mechanism of the Thiourea Dioxide-Iodate Reaction in an Acidic Medium
Autocatalysis-Driven Clock Reaction III: Clarifying the Kinetics and Mechanism of the Thiourea Dioxide-Iodate Reaction in an Acidic Medium
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自催化驱动的时钟反应 III：阐明酸性介质中二氧化硫脲-碘酸盐反应的动力学和机理
DOI：
10.1021/acs.jpca.9b00584
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发表时间：
2019-03-07
影响因子：
2.9
通讯作者：
Horvath, Attila K.
中科院分区：
文献类型：
--
作者：
Cseko, Gyorgy;Gao, Qingyu;Horvath, Attila K.
在pH为1.1-1.8、离子强度1.0M、高氯酸钠调节、温度25℃的酸性条件下，用分光光度法重新研究了二氧化硫脲-碘酸盐的反应。该体系表现出时钟行为，具有明确的和可重现的时间滞后，称为朗道时间，尽管在底物过量时甚至可以检测到元素碘；因此，在这些条件下，该反应可归类为自催化驱动的时钟反应。这清楚地表明，以前提出的动力学模型在理论和实验上都存在严重缺陷。根据反应物初始浓度比的不同，该反应可表现为S形或起伏动力学轨迹。碘极大地加速了时钟物种碘的出现，因此起到了自动催化剂的作用。库存TDO解决方案的年龄也有很大的影响，到目前为止完全被忽视的影响兰道时间。在同时评价动力学曲线的基础上，提出了一个包含5个已知的快速建立的平衡点的16步动力学模型，并用7个拟合速率系数确定了两种形式TDO的速率系数。
The thiourea dioxide-iodate reaction has been reinvestigated spectrophotometrically under acidic conditions using phosphoric acid-dihydrogen phosphate buffer within the pH range of 1.1-1.8 at 1.0 M ionic strength adjusted by sodium perchlorate and at 25 degrees C. The system was found to exhibit clock behavior, having a well-defined and reproducible time lag called Landolt time, though elementary iodine may even be detected in substrate excess; hence, under these conditions, the reaction can be classified as an autocatalysis-driven clock reaction. It is clearly demonstrated that the previously proposed kinetic model suffers from serious drawbacks from both theoretical and experimental points of view. The reaction may be characterized by either sigmoidal-shaped or rise-and-fall kinetic traces, depending on the initial concentration ratio of the reactants. Iodide significantly accelerates the appearance of the clock species iodine acting therefore as an autocatalyst. The age of stock TDO solution also has a great, so far completely overlooked impact on the Landolt time. On the basis of evaluating simultaneously the kinetic curves, a 16 step kinetic model including 5 well-known rapidly established equilibria is proposed with 7 fitted rate coefficients in which the rate coefficients of both forms of TDO were determined.