Reactions chlorite -iodide-malonic acid

Some of these chlorite oscillators exhibit particularly interesting or exotic phenomena. Batch oscillations in the absence of flow may be obtained in the systems numbered 3, 10 a and 13, while the chlorite-iodide-malonic acid reaction gives rise to spatial wave patterns as well. These latter, which are strikingly similar to those observed in the BZ reaction61 are shown in Fig. 12. Addition of iodide to the original chlorite-iodate-arsenite oscillator produces a system with an extremely complex phase diagram58, shown in Fig. 13, which even contains a region of tristability, three possible stable steady-states for the same values of the constraints. 

De Kepper, P., V. Castets, E. Dulos J. Boissonnade. 1991. Turing-type chemical patterns in the chlorite-iodide-malonic acid reaction. Physica 49D 161-69. 

Another set of pattern formation phenomena involve stationary, or Turing patterns (77), which arise in systems where an inhibitor species diffuses much more rapidly than an activator species. These patterns, which are often invoked as a mechanism for biological pattern formation, were first found experimentally in the chlorite-iodide-malonic acid reaction (72). Examples of typical spot and stripe patterns appear in Figure 3. Recently, experiments in reverse microemulsions have given rise not only to the waves and patterns described above, but to a variety of novel behaviors, including standing waves and inwardly moving spirals, as well (75). 

Figure 3. Turing patterns in the chlorite-iodide-malonic acid reaction. Dark areas show high concentrations of starch-triiodide complex. Each frame is approximately 1,3 mm square. Images courtesy of Patrick De Kepper,...

Figure 6.14 Patterns observed in the chlorite-iodide-malonic acid reaction in a Couette reactor. The CSTR composition, flow rate, and rotation rate are held fixed, except for chlorite composition in one CSTR, whieh serves as the bifurcation parameter. In each frame, the abscissa represents the position along the reactor and the ordinate represents time. The dark color results from the presence of the starch- triiodide complex. (Adapted from Ouyang et al., 1991.)...

Perraud, J, J. Agladze, K. Dulos, E, De Kepper, P. 1992, Stationary Turing Patterns versus Time-Dependent Structures in the Chlorite-Iodide Malonic Acid Reaction, Physica A 188, 1-16. 

Figure 19.10 (a) Turing structure in a one-dimensional Brusselator model, (b) Turing structures observed in chlorite-iodide-malonic acid reaction in an acidic aqueous solution (Courtesy Harry L. Swinney). The size of each square is nearly 1 mm. 

The Lengyel-Epstein model is a more realistic chemical reaction scheme. The Lengyel-Epstein model is a two-variable model for the chlorite-iodide-malonic acid (CIMA) reaction scheme and its variant, the chlorine dioxide-iodine-malonic acid (CDIMA) reaction scheme. In the model, the oscillatory behavior is related with ... 

LengyeI, I., and Epstein, I. R. (1991) Modeling of Turing structures in the chlorite-iodide-malonic acid-starch reaction. Science 251, 650. 

Lengyel, 1., Epstein, I.R. Modeling of Turing stmctures in the chlorite-iodide-malonic acid-starch reaction system. Science 251(4994), 650-652 (1991). http //dx.doi.org/10. 1126/science.251.4994.650... 

The chemical system used for our study is a chlorite-iodide-malonic acid (CIMA) reaction in an acidic (sulfuric acid) aqueous solution. The CIMA reaction exhibits a rich variety of phenomena oscillations in a batch reactor or in a CSTR [26], transient target waves in a closed Petri dish [26], bistability in a CSTR [26, 27], front structures in a Couette reactor [27-30], and Turing patterns in open gel reactors [7-10]. In our two-side-fed reactor. Figure lb, components of the reaction are distributed in the two compartments in such a way that neither compartment is separately reactive. Chlorite is only in compartment A , and malonic acid is only in compartment B thus there are opposing chemical concentration gradients in the direction normal to the plane of the gel. The other chemical species are contained in equal amounts in both reservoirs, except for sulfuric acid, which is more concentrated in compartment B than in compartment A. Note that chlorite and iodide in compartment A are at a low acid concentration they would react rapidly at high acid conditions. 

In 1990, De Kepper and colleagues in Bordeaux, working with an open unstirred gel reactor, observed the first experimental evidence for Turing structures in a chemical system, the chlorite-iodide-malonic acid (CIMA) reaction [4]. Since then this work has been verified and extended both by the Bordeaux group [11-13], and by Ouyang and Swinney [14] in Texas, using several different reactor configurations. 

The Chlorite-Iodide-Malonic Acid (CIMA) and Chlorine Dioxide-Iodine-Malonic Acid (CDIMA) Reactions... 

The reaction involving chlorite and iodide ions in the presence of malonic acid, the CIMA reaction, is another that supports oscillatory behaviour in a batch system (the chlorite-iodide reaction being a classic clock system the CIMA system also shows reaction-diffusion wave behaviour similar to the BZ reaction, see section A3.14.4). The initial reactants, chlorite and iodide are rapidly consumed, producing CIO2 and I2 which subsequently play the role of reactants . If the system is assembled from these species initially, we have the CDIMA reaction. The chemistry of this oscillator is driven by the following overall processes, with the empirical rate laws as given ... 

Despite the importance of the chlorite-iodide systems in the development of nonlinear chemical dynamics in the 1980s, the Belousov-Zhabotinsky(BZ) reaction remains as the most intensively studied nonlinear chemical system, and one displaying a surprising variety of behavior. Oscillations here were discovered by Belousov (1951) but largely unnoticed until the works of Zhabotinsky (1964). Extensive description of the reaction and its behavior can be found in Tyson (1985), Murray (1993), Scott (1991), or Epstein and Pojman (1998). There are several versions of the reaction, but the most common involves the oxidation of malonic acid by bromate ions BrOj in acid medium and catalyzed by cerium, which during the reaction oscillates between the Ce3+ and the Ce4+ state. Another possibility is to use as catalyst iron (Fe2+ and Fe3+). The essentials of the mechanisms were elucidated by Field et al. (1972), and lead to the three-species model known as the Oregonator (Field and Noyes, 1974). In this... 

Quasi-two-dimensional structure in CIMA reaction (chlorite - - iodide -t- malonic acid -I- starch). Initially transient yellow circles emerge and start to grow in a blue surrounding. These structures dissolve and break into dot patterns demonstrating a wide distribution of sizes. The dots evolve to a stationary structure consisting of yellow hexagons of different orientations [51, 52]. Similar structures have been observed in petri dish experiments with PA-MBO reaction [53]. 

Only the BZ reaction has played a more central role in the development of nonlinear chemical dynamics than the chlorite-iodide reaction (De Kepper et al., 1990). This latter system displays oscillations, bistability, stirring and mixing effects, and spatial pattern formation. With the addition of malonic acid, it provides the reaction system used in the first experimental demonstration of Turing patterns (Chapter 14). Efforts were made in the late 1980s to model the reaction (Epstein and Kustin, 1985 Citri and Epstein, 1987 Rabai and Beck, 1987), but each of these attempts focused on a different subset of the experimental data, and none was totally successful. Since each model contains a different set of reactions fitted to a different set of data, individual rate constants vary widely among the different models. For example, the rate constant for the reaction between HOCl and HOI has been given as zero (Citri and Epstein, 1987), 2 x10 s (Rabai... 

Historically, it was the CIMA reaction in which Turing patterns were first found. Under the conditions of these experiments, however, our analysis suggests that, after a relatively brief initial period, it is really the CDIMA reaction that governs the formation of the patterns. Even when the input feeds consist of chlorite and iodide, chlorine dioxide and iodine soon build up within the gel and play the role of reactants whose concentrations vary relatively slowly compared with those of C102 and I . We have therefore found it more practical to work with the CDIMA system, using chlorine dioxide and iodine along with malonic acid as the input species, since in this way the relevant parameters can more easily be measured and controlled. Working with the CDIMA system also leads us naturally toward a simpler version of the model described by eqs. (14.22)-( 14.24). 

The initial reagents of the CIMA reaction are chlorite (CIOJ), iodide (I ), and malonic acid (CH2(COOH)2). The overall reaction consists of the oxidation of iodide by chlorite complicated by the iodination of malonic acid. The oscillatory mechanism of the reaction was elucidated by Lengyel et al. [60]. They found that the oscillatory dynamics actually occurred when the initial chlorite and iodide ions were nearly completely consumed. Thereafter, besides the malonic acid, the major species are chlorine dioxide (CIO2) and iodine (I2) while iodide and chlorite become the true variables and play respectively the roles of the activator and of the inhibitor . 

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