Classification of Clock Reactions

Horváth, Attila; Nagypál, Ištván

doi:10.1002/cphc.201402806

Cited by 54 publications

(78 citation statements)

References 43 publications

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“…When parallel experiments were performed under ''exactly the same experimental conditions'' in the chlorite-thiosulfate 1 and iodide-chlorite 2 reactions, the products of chlorine dioxide and iodine, respectively, appeared after a fairly long but strongly irreproducible time lag, making the reactions later be classified as crazy-clock reactions. 3 The phenomenon became the subject of great interest when Soai et al reported the discovery of asymmetric amplification in an autocatalytic reaction in 1995, 4 followed by their subsequent study on the stochastic nature of enantiomerically enriched pyrimidyl alkanol obtained from the reaction of pyrimidine-5carbaldehyde and diiodopropylzinc. 5 Since then, these reactions have became the prototypes of stochastic chemical systems.…”

Section: Introductionmentioning

confidence: 99%

Imperfect mixing as a dominant factor leading to stochastic behavior: a new system exhibiting crazy clock behavior

Valkai

Horváth

2018

Phys. Chem. Chem. Phys.

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It is clearly demonstrated that the arsenous acid-periodate reaction displays crazy-clock behavior when a statistically meaningful number of kinetic runs are performed under "exactly the same" conditions. Both extensive experimental and numerical simulation results gave convincing evidence that the stochastic feature of the title reaction originates from the imperfection of the mixing process, and neither local random fluctuation nor initial inhomogeneity alone is capable of explaining adequately the observed phenomena. Imperfect mixing is manifested-in practice-in the unintentional and inherent formation of dead volumes where the concentration of the reactants may even significantly differ from the ones measured in the case of a completely uniform concentration distribution, and the system may spend enough time there under imperfectly mixed conditions to complete the nonlinear chemical process. Furthermore, it is also shown that a more efficient mixing, i.e. a smaller dead volume size and shorter residence time being spent in the dead volume, does not necessarily mean Landolt times are smaller than the one measured under completely homogeneous conditions. Evidently, the "initial" concentration of the reagents in the dead volume-and of course in the rest of the solution-greatly influences the Landolt time to be measured in the case of an individual kinetic run and may therefore show either positive or negative deviation from the Landolt time for the completely homogeneous state. As a result, less efficient mixing may either accelerate or decelerate the rate of a nonlinear autocatalytic reaction at a macroscopic volume level.

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Section: Introductionmentioning

confidence: 99%

Imperfect mixing as a dominant factor leading to stochastic behavior: a new system exhibiting crazy clock behavior

Valkai

Horváth

2018

Phys. Chem. Chem. Phys.

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“…10 It consists of a slow direct reaction between the reactants producing the autocatalyst (usually iodide ion) which then gives rise to the appearance of iodine by the Dushman reaction. 12 When the rate of production of iodine overtakes that of its removal the appearance of iodine rings the bell for the clock behavior. The relative rate difference of the substrate-iodine reactions recently provided an opportunity to classify clock reactions.…”

Section: Introductionmentioning

confidence: 99%

Initial inhomogeneity-induced crazy-clock behavior in the iodate–arsenous acid reaction in a buffered medium under stirred batch conditions

Valkai

Csekõ

Horváth

2015

Phys. Chem. Chem. Phys.

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It is unambiguously demonstrated that in the case of an autocatalytic reaction, initial inhomogeneities induced by the imperfectly mixed part of the overall volume may result in a serious irreproducibility of the individual kinetic runs. A statistically meaningful number of repetitions, however, gives rise to a reproducible cumulative probability distribution curve often referred to as a support of the stochastic feature. The iodate-arsenous acid reaction being autocatalytic with respect to both iodide and hydrogen ions displays clock behavior. However, the time lag necessary for the appearance of iodine, even in buffered solution, varies in an apparently random manner. Careful analysis of the variation of the different parameters like stirring rate, overall volume, geometry of the reactor and the way of mixing the reactants led us to conclude that the fate of the individual samples is determined at the initial stage when the reacting system is per se inhomogeneous. The place, the size of the so-called ignition volume, where the reacting system is imperfectly stirred, as well as the residence time spent there by the imperfectly mixed reactants all seem to depend on external factors.

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“…It is well understood that removal of an inhibitor without autocatalysis can result in rapid production of a species after a time lag. 17,18 However there is an important difference in these two cases. With autocatalysis, both the rate of production of acid and the rate of removal of substrate, aqueous ester, accelerate in time.…”

Section: Resultsmentioning

confidence: 99%