Chlorite-iodide reaction

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 ... 

Fox, R. O., G. Erjaee, and Q. Zou (1994). Bifurcation and stability analysis of micromixing effects in the chlorite-iodide reaction. Chemical Engineering Science 49, 3465-3484. 

Fig. 3. Schematic diagram of a CSTR. In the configuration shown, up to three different solutions can be pumped (by the peristaltic pump, PP) into the reactor, R. The detectors shown in the diagram are , light absorption (A/, monochromator PM, photomultiplier), platinum (redox), and iodide (or bromide) selective electrodes. The reference electrode is the Hg/Hg2S04 couple, in place of the usual calomel electrode, to avoid adventitious introduction of chloride into the reactor. In addition to these detectors, a thermocouple, or thermistor, and a pH electrode can be inserted into the reactor from above. The recordings of periodic behavior were taken from studies on the chlorite-iodide reaction...

The two systems we combined are the arsenite-iodate and the chlorite-iodide reactions. We first describe the arsenite subsystem. 

Rate laws for the two phases - growth and decay of iodine - of the chlorite-iodide reaction have been determined50,51,53), and are collected in Table 4. For the purposes of... 

Table 7. Some mechanistic steps in the chlorite-iodide reaction...

Oscillators, Part 5. Bistability and Oscillations in the Autocatalytic Chlorite-Iodide Reaction in a Stirred-Flow Reactor, J. Am. Chem. Soc. 104(2) 504-509... 

We close this Section by mentioning that, despite initial controversies, the most complex type of dynamic behavior, chaos, has been shown to be also present in chemical systems, among which the most studied is again the BZ reaction (Scott, 1991). Chaos has also been observed, for example, in the chlorite-thiosulfate or the bromate-chlorite-iodide reactions, or in the gas-phase reaction between carbon monoxide and oxygen (Epstein and Pojman, 1998). 

M. Menzinger and A.K. Dutt. On the myth of the well-stirred reactor, the chlorite/iodide reaction. J. Phys. Chem., 94 4510, 1990. 

De Kepper P, Boissonade J and Epstein I R 1990 Chlorite-iodide reaction a versatile system for the study of nonlinear dynamical behaviour J. Phys. Chem. 94 6525-36... 

Citri, O. I.R. Epstein. 1988. Mechanistic study of a coupled chemical oscillator The bromate-chlorite-iodide reaction./. Phys. Chem. 92 1865-71. 

Citri, O. Epstein, I. R. Systematic design of chemical oscillators. 42. Dynamic behavior in the chlorite-iodide reaction a simplified mecfianism. J. Phys. Chem. 1987, 91, 6034—6040. 

The ranges of various dynamic regimes are often displayed in a two-dimensional (2D) bifurcation diagram. An example is given in fig. 11.1, obtained by calculation [5] from a model of the chlorite-iodide reaction [39,40] the 2D space of constraints in... 

An example of such a comparison is seen in the modeling of the oscillating chlorite-iodide reaction. The model initially proposed by Epstein and Kustin [39] showed only fair agreement with the experimentally observed 1 evolution, and worse agreement with the experimentally observed I2 evolution, as seen in fig. 11.5(a,b). A revised mechanism proposed by Citri and Epstein [40] predicts oscillations quite similar in shape to the experimentally observed 1 and I2 oscillations (fig. 11.5c). In many oscillatory systems the temporal variation of only a few species (essential or nonessential) can be measured. The comparison of an experimental time series with a prediction of a proposed mechanism can be made with regard to the period of the oscillations, but becomes subjective with regard to the shape of the variation. The comparisons do not easily lead to suggestions for improvements of the proposed reaction mechanism. 

Fig. 11.5 Comparison of experimental and theoretical oscillatory traces of I2 absorbance and 1 potential for the chlorite-iodide reaction, (a) Experimental traces, (b) Theoretical traces from the Epstein-Kustin mechanism show fair qnahtative agreement, bnt wave shapes are snb-stantially different from experimental observations, (c) Theoretical traces from the Citri-Epstein mechanism show marked improvement in wave shape agreement with experiments. (Erom [2].)...

The chlorite-iodide reaction has been found by Dateo et al. [79] and later by De Kepper et al. [80] to exhibit complex phenomena such as oscillations and bistability between steady states, when run in a continuous-flow stirred tank reactor (CSTR). The overall stoichiometry of the reaction is... 

Fig. 11.1 5 The experimentally determined bifnrcation structure of the chlorite-iodide reaction. The two constraints used here are the ratio of input concentrations, [CIO2 ]o/[I ]o> and the logarithm of the reciprocal residence time, log k(,. Notation filled triangles, supercritical Hopf bifurcations filled circles, saddle-node infinite period bifurcations in the region between these two kind of bifurcations, stable oscillations were observed. Open circles, excitable dynamics the smallest circles correspond to perturbations of 2 x 10 M in NaC102 the next smallest, 6 X 10 M in NaC102 the next smallest, 1.25 x 10 X x oMn - o io-2 1...

Stemwedel, J. Ross, J. New measurements on the chlorite iodide reaction and deduction of roles of species and categorization. J. Phys. Chem. 1995, 99, 1988-1994. 

Luo, Y Epstein, 1. R. Systematic design of chemical oscillators. 38. Stirring and premixing effects in the oscillatory chlorite-iodide reaction. J. Chem. Phys. 1986, 85, 5733-5740. 

High iodide state , low iodide state O, bistability O, oscillation. (Reprinted with permission from De Kepper, P. Boissonade, J. Epstein, I. R. 1990. Chlorite-Iodide Reaction A Versatile System for the Study of Nonlinear Dynamical Behavior, J. Phys. Cfiem. 94, 6525-6536.)... 

Figure 3.3 In developing a model of the chlorite-iodide reaction, Epstein and Kustin studied the reaction in a batch reactor. (Adapted from Epstein and Kustin, 1985.)...

Figure 4.9 Bistability in the chlorite-iodide reaction as measured by (a) 460-nm absorbance (proportional to [I2]) and (b) an iodide-selective electrode. Dashed arrows indicate spontaneous transitions between states. Reciprocal residence time in CSTR = 5.4 X 10-- s-, [ClOjjo = 2.4 X 10-" M, pH = 3.35. (Adapted from Citri and Epstein, 1987.)...

The first systematic design of a chemical oscillator had been achieved There remained some ambiguity, however. Since two autocatalytic reactions had been employed, it was not immediately clear which constituted the fundamental autocatalytic reaction and which provided the feedback in the model scheme. Historically, the arsenite-iodate system had been chosen for the former role, since its bistable behavior had been established first. More careful investigation revealed that, in fact, it was the chlorite-iodide reaction that provides the essential dynamical features of this system. The evidence comes in two forms. First, the chlorite-iodide reaction is also bistable in a CSTR (Dateo et al., 1982) and the relaxation to its steady states is more rapid than the relaxation behavior of the arsenite iodate system. According to our theory,... 

The chlorite-iodide reaction is clearly the minimal oscillator of the subfamily of chlorite-iodide xidant oscillating reactions, and, since iodate and iodine appear to be produced in all of them, it can be considered to be the progenitor of a still larger family that includes the chlorite-iodate-reductant and cWorite-iodine-reductant groups listed in Table 4.1. Clearly, the chlorite-iodide reaction cannot be minimal for the entire family of chlorite-based oscillators since many of them contain no iodine species. It is not at all obvious that a minimal oscillator for the entire chlorite family exists. 

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... 

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