Oscillator bromate

IIIC, D) Orban, M., De Kepper, P., Epstein, I. R. Systematic Design of Chemical Oscillators, 1982-2 Part 10. Minimal Bromate Oscillator Bromate-Bromide-Catalyst. J. Am. Chem. Soc. 104(9) 2657-2658... 

R) Zhabotinsky, A. M. Oscillating Bromate Oxidative Reactions. Ber. Bunsenges. Phys. 1980 Chem. 84(4) 303-308... 

J, Maselko, M. Alamgir and I. R. Epstein, Bifurcation analysis of a system of coupled chemical oscillators bromate-chlorite-iodite . Physica, 19D, 153 (1986). 

Maselko, J. Alamgir, M. Epstein, I. R. 1986. Bifurcation Analysis of a System of Coupled Oscillators Bromate Chlorite-Iodide, Physica 19D, 153-161. 

The existence of chaotic oscillations has been documented in a variety of chemical systems. Some of tire earliest observations of chemical chaos have been on biochemical systems like tire peroxidase-oxidase reaction [12] and on tire well known Belousov-Zhabotinskii (BZ) [13] reaction. The BZ reaction is tire Ce-ion-catalyzed oxidation of citric or malonic acid by bromate ion. Early investigations of the BZ reaction used tire teclmiques of dynamical systems tlieory outlined above to document tire existence of chaos in tliis reaction. Apparent chaos in tire BZ reaction was found by Hudson et a] [14] aiid tire data were analysed by Tomita and Tsuda [15] using a return-map metliod. Chaos was confinned in tire BZ reaction carried out in a CSTR by Roux et a] [16, E7] and by Hudson and... 

For demonstrations add to a 1 -L beaker, 600 mL water, 60 mL cone, sulfuric acid, 20 g malonic acid, 7.8 g potassium bromate, 0.7-0.8 g (NHj ),Ce(NCL), and about 1 mL 0.025 M [Fe(phen)i]S04 ( ferroin indicator) to give a visible color. Stir magnetically. A short but variable length of time can be expected before oscillations begin their frequency depends on the temperature. 

Belouzov-Zhabotinsky reaction [12, 13] This chemical reaction is a classical example of non-equilibrium thermodynamics, forming a nonlinear chemical oscillator [14]. Redox-active metal ions with more than one stable oxidation state (e.g., cerium, ruthenium) are reduced by an organic acid (e.g., malonic acid) and re-oxidized by bromate forming temporal or spatial patterns of metal ion concentration in either oxidation state. This is a self-organized structure, because the reaction is not dominated by equilibrium thermodynamic behavior. The reaction is far from equilibrium and remains so for a significant length of time. Finally,... 

Field, R.J., Noyes, R.M., and Koros, E., Oscillations in chemical systems. 2. Thorough analysis of temporal oscillation in bromate-cerium-malonic acid system, JACS, 94,8649,1972. 

The Belousov-Zhabotinskii reaction is a typical oscillating chemical reaction. Spiral structures form periodically, disappear and reappear as the result of an autocatalytic reaction, the oxidation of Ce3+ and Mn2+ by bromate (lessen, 1978). 

The oscillation regime is observed in the oxidation of the iodide ions by the BrCfi ions. The kinetics of this reaction and its mechanism were studied in detail by Citri and Epstein [223]. The process was studied in a jet reactor. The oscillating regime is observed when the concentration of iodide ions changes in an interval of 5 x 10 7 to 4 x 10 2 M (bromate was introduced in excess with respect to the iodide ions). The example of the oscillating kinetic curve can be seen in Figure 10.1. 

An acidic bromate solution can oxidize various organic compounds and the reaction is catalyzed by species like cerous and manganous ions that can generate 1-equivalent oxidants with quite positive reduction potential. Belousov (1959) first observed oscillations in Celv]/[Cem] during Ce (III) catalysed oxidation of citric acid by bromate ion. Zhabotinskii made extensive studies of both temporal and spatial oscillations and also demonstrated that instead of Ce (III), weak 1- equivalent reductants like Mn(II) and Fe (II) can also be used. The reaction is called Belousov-Zhabotinskii reaction. This reaction, most studied and best understood, can be represented as... 

The main processes occurring in this system are the following [219] bromate oxidizes trivalent cerium to tetravalent cerium Ce4+ oxidizes bromomalonic acid, and is reduced to Ce3+. The bromide ion, which inhibits the reaction, is isolated from the oxidation products of bromomalonic acid. During the reaction, the concentration of the Ce4+ ions (and Ce3+) oscillates several times, passing through a maximum and a minimum. The shape of the peaks of concentrations and the frequency depend on the reaction conditions. The autooscillation character of the kinetics of the cerium ions disappears if Ce4+ or Br are continuously introduced with a low rate into the reaction mixture. The autooscillation regime of the reaction takes place only in a certain interval of concentrations of the reactants [malonic... 

The Belousov-Zhabotinskii reaction is a cerium-catalyzed oxidation of malonic acid by bromate, in which the quotient [Ce3+]/[Ce4+] oscillates by a factor of 10 to 100.8... 

Numerous versions of the Belousov-Zhabotinsky system differ by chemical compounds used. The typical reaction involves oxidation of some organic compound by bromate ion (BrOj ) occurring in acid medium with metal catalyst (Ce3+, Mn2+, as well as complexes of Fe2+, Ru2+). As an example, a particular reaction [4] could be mentioned, where an organic reductor is malonic acid CH2(COOH)2 and Ce3+ ions serve as a catalyst. In this reaction a solution changes periodically its colour due to oscillations in Ce3+ concentration. Generally speaking, the reaction consists of two stages. At the first one metal is oxidized... 

The phrase laboratory curiosity was an apt characterization of a reaction that first saw the light of day in the late 1950 s1. This reaction - the acidic oxidation of citric acid by bromate in the presence of the dual catalysts bromide and cerium(IV)/(III) - displays oscillations in the concentrations of two component species in the course of proceeding towards completion. Curiosity and skepticism were engendered by oscillation in a homogeneous reaction mixture, even though such observations had been well documented in the past. 

Prior to our systematically designed oscillators, the inorganic oscillator most intensively studied was the BZ reaction. Examination of this reaction and the FKN mechanism reveals several features helpful to achieving an appreciation for the construction of a chemical oscillator. The driving force for the BZ reaction is the reduction of bromate and the associated oxidation of malonic acid (MA) to carbon dioxide. The stoichiometry is not that simple, however, since bromomalonic acid is also produced in the reaction, and can be oxidized to formic acid. A possible stoichiometry is... 

The chlorite-iodate-arsenite oscillator was the first oscillating reaction discovered which is based upon chlorite chemistry. The BZ reaction and its relatives are bromate oscillators, while the BL and Briggs-Rauscher oscillators are iodate systems. The initial chlorite oscillator was rapidly followed by a large family of related systems58"60, which are summarized in Table 8. We note that while most of these systems contain an iodine species (I-, I2, IOf) as well as the chlorite, at least two iodine-free chlorite oscillators exist. 

D) Iodine-free chlorite oscillators. In view of our almost total ignorance of how the chlorite-thiosulfate system functions, we place it for the moment in a class of its own, though further study may ultimately situate it in an expanded category A. The recently discovered chlorite-bromide-bromate oscillator may be analogous to the chlorite-iodide-iodate system of class A ) above, though one may view it alternatively as a bromate driven oscillator in which CIOJ plays the role of the metal catalyst. 

At the start, the cycle begins with a certain amount of Ce+4 ions. The second reaction provides Br- ions, which inhibit the first reaction. This leads to an increase in concentration of Ce+3. After reaching a certain amount of Ce+3, the oxidation reaction starts, since little Ce+4 remains. The system can no longer produce sufficient Br to inhibit the reaction, and Ce+3 decreases rapidly, producing Ce+4 until the cycle is completed. It is possible to maintain indefinite oscillations with constant frequency in a continuous flow stirred reactor into which bromate, malonic acid, and cerium catalyst are being supplied at a uniform rate. 

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