On the Kinetics and Mechanism of the Thiourea Dioxide–Periodate Autocatalysis-Driven Iodine-Clock Reaction

Csekõ, György; Gao, Qingyu; Pan, Chunyu; Xu, Li; Horváth, Attila

doi:10.1021/acs.jpca.9b06207

Cited by 7 publications

(6 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The ratio of these rate coefficients provides the p K a1 of phosphoric acid to be 1.8 . This value worked consistently well in a number of previous systems investigated. − …”

Section: Discussionsupporting

confidence: 75%

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

Csekõ

Horváth

2020

J. Phys. Chem. A

Self Cite

View full text Add to dashboard Cite

The methionine–iodine reaction was reinvestigated spectrophotometrically in detail monitoring the absorbance belonging to the isosbestic point of iodine at 468 nm, at T = 25.0 ± 0.1 °C, and at 0.5 M ionic strength in buffered acidic medium. The stoichiometric ratio of the reactants was determined to be 1:1 producing methionine sulfoxide as the lone sulfur-containing product. The direct reaction between methionine and iodine was found to be relatively rapid in the absence of initially added iodide ion, and it can conveniently be followed by the stopped-flow technique. Reduction of iodine eventually leads to the formation of iodide ion that inhibits the reaction making the whole system autoinhibitory with respect to the halide ion. We have also shown that this inhibitory effect appears quite prominently, and addition of iodide ion in the millimole concentration range may result in a rate law where the formal kinetic order of this species becomes −2. In contrast to this, hydrogen ion has just a mildly inhibitory effect giving rise to the fact that iodine is the kinetically active species in the system but not hypoiodous acid. The surprisingly complex kinetics of this simple reaction may readily be interpreted via the initiating rapidly established iodonium-transfer process between the reactants followed by the subsequent hydrolytic decomposition of the short-lived iodinated methionine. A seven-step kinetic model to be able to describe the most important characteristics of the measured kinetic curves is established and discussed in detail.

show abstract

“…The ratio of these rate coefficients provides the p K a1 of phosphoric acid to be 1.8 . This value worked consistently well in a number of previous systems investigated. − …”

Section: Discussionsupporting

confidence: 75%

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

Csekõ

Horváth

2020

J. Phys. Chem. A

Self Cite

View full text Add to dashboard Cite

show abstract

“…When FDS and TMO are completely consumed, this balance is gradually lost. As a result, the TDO–iodate autocatalysis-driven clock reaction takes control of increasing the amount of iodine in stage IV . Once iodate is removed completely, thiourea dioxide is still present in the solution and ready to remove iodine in the fairly long thiourea dioxide–iodine reaction that was found to be autoinhibited by the iodide ion, resulting in stage V .…”

Section: Results and Discussionmentioning

confidence: 99%

Compatible Kinetic Model for Quantitative Description of Dual-Clock Behavior of the Complex Thiourea–Iodate Reaction

2023

Self Cite

View full text Add to dashboard Cite

The thiourea−iodate reaction has been investigated simultaneously by ultraviolet−visible spectroscopy and high-performance liquid chromatography (HPLC). Absorbance−time traces measured at the isosbestic point of the iodine−triiodide system have revealed a special dual-clock behavior. During the first kinetic stage of the title reaction, iodine suddenly appears only after a well-defined time lag when thiourea is totally consumed due to the rapid thiourea−iodine system giving rise to a substrate-depletive clock reaction. After this delay, iodine in the system starts to build up suddenly to a certain level, where the system remains for quite a while. During this period, hydrolysis of formamidine disulfide as well as the formamidine disulfide−iodine system along with the Dushman reaction and subsequent reactions of the intermediates governs the parallel formation and disappearance of iodine, resulting in a fairly constant absorbance. The kinetic phase mentioned above is then followed by a more slowly increasing sigmoidally shaped profile that is characteristic of autocatalysis-driven clock reactions. HPLC studies have clearly shown that the thiourea dioxide−iodate system is responsible mainly for the latter characteristics. Of course, depending on the initial concentration ratio of the reactants, the absorbance−time curve may level off or reach a maximum followed by a declining phase. With an excess of thiourea, iodine may completely disappear from the solution as a result of the thiourea dioxide−iodine reaction. In the opposite case, with an excess of iodate, the final absorbance reaches a finite value, and at the same time, iodide ion will disappear completely from the solution due to the well-known Dushman (iodide−iodate) reaction. In addition, we have also shown that in the case of the formamidine disulfide− iodine reaction, unexpectedly the triiodide ion is more reactive toward formamidine disulfide than iodine. This feature can readily be interpreted by the enhancement of the rate of formation of the transition complex containing oppositely charged reactants. A 25-step kinetic model is proposed with just 10 fitted parameters to fit the 68 kinetic traces measured in the thiourea−iodate system and the second, but slower, kinetic phase of the thiourea−iodine reaction. The comprehensive kinetic model is constituted in such a way as to remain coherent in quantitatively describing all of the most important characteristics of the formamidine disulfide−iodine, thiourea dioxide−iodine, and thiourea dioxide−iodate systems.

show abstract

“…M25 : This reaction is the first step for the production of iodine and HIO 2 by the HIO 3 –iodide reaction. The rate constants we used are the same as those used in refs and to model the thiourea dioxide–iodate clock reaction and the thiourea dioxide–periodate clock reaction, respectively, which gives an equilibrium constant for the formation of I 2 O 2 equal to 0.1. This equilibrium constant is significantly lower than the value used by Agreda B. et al which considered the formation of the intermediate H 2 IO 3 + , splitting this reaction in two steps.…”

Section: Discussionmentioning

confidence: 99%

“…M26 : This reaction is the second step for the production of iodine and HIO 2 by the HIO 3 –iodide reaction, considering the reaction between the intermediate I 2 O 2 and iodide. The rate constants we used are the same as those used in refs and to model the thiourea dioxide–iodate clock reaction and the thiourea dioxide–periodate clock reaction, respectively, considering two paths for this reaction, one of which includes the participation of H + in the rate law and the other which does not include participation of H + . In contrast, Agreda B. et al considered that I 2 O 2 is in equilibrium with H 2 I 2 O 3 (the hydrated form of I 2 O 2 ), and this species reacts with iodide to form iodine and HIO 2 after three steps.…”

Section: Discussionmentioning

confidence: 99%

The Photochemical Chlorate–Iodide Clock Reaction

Pires

Faria

2021

Inorg. Chem.

View full text Add to dashboard Cite

Mixing iodide and perchloric acid solutions with an excess of chlorate inside a diode-array spectrophotometer led to the observation of an abrupt decrease of the absorbance at the 215 nm isosbestic point after an induction period. The clock time decreases by increasing the initial concentrations of chlorate and acid, but increasing the initial iodide concentration has an opposite effect. The proposed mechanism simulates the experimental results and considers the interaction of UV light with iodide, producing iodine and triiodide ion. The autocatalytic core of this mechanism is the same as that employed to explain the autocatalytic behavior of chlorine dioxide–iodine reaction, but considering H2IO+ as the reactive species rather than HOI, being a more realistic mechanism for acid conditions.

show abstract

On the Kinetics and Mechanism of the Thiourea Dioxide–Periodate Autocatalysis-Driven Iodine-Clock Reaction

Cited by 7 publications

References 35 publications

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

Compatible Kinetic Model for Quantitative Description of Dual-Clock Behavior of the Complex Thiourea–Iodate Reaction

The Photochemical Chlorate–Iodide Clock Reaction

Contact Info

Product

Resources

About