Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide-Bromate Substrate-Depletive Clock Reaction
Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide-Bromate Substrate-Depletive Clock Reaction
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二氧化硫脲-溴酸盐底物消耗时钟反应中兰多尔特时间的精确浓度依赖性
DOI：
10.1021/acs.jpca.9b02025
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发表时间：
2019
影响因子：
2.9
通讯作者：
Horvath Attila K.
中科院分区：
文献类型：
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作者：
Cseko Gyorgy;Gao Qingyu;Takacs Attila;Horvath Attila K.
采用磷酸-磷酸二氢缓冲液，在pH 1.1 ~ 1.8范围内，高氯酸钠调节离子强度1.0 M，温度25℃，用分光光度法研究了硫脲-溴酸盐的酸性反应。标题体系与经典的Landolt反应有显著的相似之处，即时钟物质（溴）只有在底物TDO完全消耗后才会出现。因此，标题系统可归类为底物消耗时钟反应。尽管众所周知，TDO在酸性溶液中重排缓慢，但令人惊讶的是，标题反应的Landolt时间完全不依赖于应用TDO溶液的年龄。然而，实验表明，朗多尔时间的逆线性依赖于初始溴酸盐浓度以及氢离子浓度的平方。除此之外，我们还注意到磷酸二氢对Landolt时间也有显著的影响，这一特征很容易被溴酸盐-溴化反应速率对h2po4的依赖定量考虑。在实验的基础上，提出了一个简单的三步动力学模型，并由此导出了一个复杂的公式，以精确地表示朗多尔时间与浓度的依赖关系。
The thiourea dioxide (TDO)–bromate 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 °C. The title system shows a remarkable resemblance to the classical Landolt reaction, namely, the clock species (bromine) may only appear after the substrate TDO is completely consumed. Thus, the title system can be classified as substrate-depletive clock reaction. Despite the well-known slow rearrangement characteristic of TDO in acidic solution, it is surprisingly found that the Landolt time of the title reaction does not depend at all on the age of TDO solution applied. It is, however, shown experimentally that the inverse of Landolt time linearly depends on the initial bromate concentration as well as on the square of the hydrogen ion concentration. In addition to this, it is also noticed that dihydrogen phosphate markedly affects the Landolt time as well, and this feature may easily be taken into consideration by the H2PO4–dependence of the rate of bromate–bromide reaction quantitatively. Based on the experiments, a simple three-step kinetic model is proposed from which a complex formula is derived to indicate the exact concentration dependence of the Landolt time.