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The Transition from Low to High Iodide and Iodine Concentration State in the Briggs Rauscher Reaction – Evidence on Crazy Clock Behavior Maja Cvetko Pagnacco, Jelena Petronije Maksimovi#, Nebojsa I. Potkonjak, Bojan #. Boži#, and Attila K. Horváth J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b11774 • Publication Date (Web): 18 Dec 2017 Downloaded from http://pubs.acs.org on December 25, 2017
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The Journal of Physical Chemistry
The Transition from Low to High Iodide and Iodine Concentration State in the Briggs Rauscher Reaction – Evidence on Crazy Clock Behavior
Maja C. Pagnacco1*, Jelena P. Maksimović1, Nebojša I. Potkonjak2, Bojan Đ. Božić3, Attila K. Horváth4
1
Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, P.O. Box 47, 11158 Belgrade, Serbia
2
Chemical Dynamics Laboratory, Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia 3
Institute of Physiology and Biochemistry, Faculty of Biology, University of Belgrade, Studentski trg 16, 11000 Belgrade, Serbia
4
Department of Inorganic Chemistry, University of Pécs, Ifjúság u. 6, H-7624 Pécs, Hungary
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Abstract
The Briggs-Rauscher reaction containing malonic acid may undergo a sudden transition from low (state I) to high iodide and iodine (state II) concentration states after a well-defined and strongly reproducible oscillatory period. This study clearly shows that even though the time-dependent behavior of the oscillatory state is reproducible, the time lag necessary for the appearance of the state I to state II transition after the system leaves the oscillatory state becomes irreproducible for an individual kinetic run. This crazy clock behavior of the state I→state II transition is identified by repeated experiments, in which stirring rate is taken as a control parameter and all other parameters such as initial conditions, temperature, vessel surface and the age of solution were kept constant. Surprisingly, a better stirring condition does not make the transition to be reproducible; it simply does not allow the transition to happen at all. The proposed mechanism, additional explanations as well as proposals for this irreproducibility of state I to state II transition have been presented. Considering the fact that the number of crazy-clock reactions is only a few, this study may contribute to a better understanding of fundaments of this phenomenon.
*
Corresponding author e-mail:
[email protected] or
[email protected] Maja C. Pagnacco, Ph.D.,
University of Belgrade, Faculty of Physical Chemistry ORCID ID: 0000-0002-1299-7974
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The Journal of Physical Chemistry
1. Introduction
The Briggs-Rauscher (BR) reaction is one of the most dramatic oscillating chemical reaction, in which the oxidation of malonic acid (CH2(COOH)2), induced by a mixture of hydrogen peroxide (H2O2) and potassium iodate (KIO3), is catalyzed by manganese(II) ion (Mn2+) in acidic (H2SO4) aqueous solution1-4: 𝑀𝑛2+ 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡
CH2(COOH)2 + IO3- + 2H2O2 + H+ →
CHI(COOH)2 + 2O2 + 3H2O
(1)
When using starch as an indicator, this reaction becomes visually impressive, due to the occurrence of cyclical alternating color transitions: colorless → amber yellow → dark blue, before ending as a dark blue mixture.5 The BR reaction system can be considered as a hybrid of two well-known chemical oscillating reactions, the Bray-Liebhafsky6-8 and the BelousovZhabotinsky reaction9-11. Oscillatory phenomena of the BR reaction have been broadly investigated from several aspects, such as an effect of various substitutions and additions,12-18 an examination of subsystems, mechanism, and bistability2-4,19. However, oscillatory state (state Os) is not the only interesting nonlinear phenomenon appearing in the BR reaction. Depending on the initial concentrations, particularly on the ratio R = [CH2(COOH)2]0/[IO3-]0, the ending mode of the BR system can be divided into two distinct cases; the state I, characterized by low [I2] and [I-], and R=2 (depending on other concentrations), and the state II, characterized by high [I2] and [I-] and R
