Oscillator chlorite

Therefore to induce the oscillations chlorite is introduced. For a certain range of initial KI03 and NaC102 and As203 concentrations oscillations in I- concentration were observed. 

Oscillators, Part 4. New Family of Homogeneous Chemical Oscillators-Chlorite-Iodate-Substrate. Nature (London) 292,816-818... 

Alamgir, M. I.R. Epstein. 1983. Birhythmicity and compound oscillations in coupled chemical oscillators Chlorite-Bromate-Iodide system. J. Am. Chem. Soc. 105 2500-1. 

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. 

Figure 12.3 Phase diagram of the bromate-chlorite-iodide reaction in the /co-[I ]o plane. Fixed constraints [BrO Jo = 2.5 x 10 M, [ClOJJo = 1.0 x 10 M, [H2S04]o = 0.75 M. Symbols open circles, low-frequency oscillatory state filled circles, high-frequency oscillatory state open triangles, low-potential stationary state filled triangles, high-potential stationary state open squares, intermediate-potential stationary state. Combinations of two symbols imply bistability between the corresponding states. (Reprinted with permission from Alamgir, M. Epstein, I. R. 1983. Birhythmidty and Compoimd Oscillation in Coupled Chemical Oscillators Chlorite—Bromate-Iodide System, J. Am. Chem. Soc. 105, 2500-2502. 1983 American Chemical Society.)...

Alamgir, M. Epstein, I. R. 1985b. New Chlorite Oscillators Chlorite-Bromide and Chlorite-Thiocyanate in a CSTR, J. Phys. Chem. 89, 3611-3614,... 

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 ... 

Table 4. Component processes of the arsenite-iodate-chlorite oscillator and their rate laws1...

The very narrow region of the constraint space where oscillations could occur in this system was not found until after the chlorite-iodate-arsenite oscillator had been discovered. Its occurrence is shown in the cross-shaped diagram for chlorite-iodide (Fig. 8.)... 

The development of an adequate mechanism for the BZ reaction required nearly 15 years from the discovery of oscillations in that system, and refinement of that mechanism is still under way56. It is a measure of the progress in the field of oscillating reactions that only 15 months after the design of the first chlorite oscillator, a mechanism for that system seems well within reach. Without setting forth a full mechanistic treatment, which is not yet available, we sketch here what we believe to be the key elements in the oscillation of the chlorite-iodate-arsenite oscillator and, by extension, several of the related systems to be discussed below. A partial mechanism for the prototype chlorite-iodide system will be presented in the following section. 

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. 

C102 -10 J-H3ASO3 First chlorite oscillator discovered 55... 

CIO2 SjO] First iodine-free chlorite oscillator 60... 

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. 

In an effort to produce a general scheme for understanding and categorizing chlorite-iodine oscillators, Orbdn et al.58 have developed a set of component stoichiometric... 

With this framework of component processes in mind, Orbdn et al.58) proposed the following preliminary classification of chlorite oscillators ... 

A) Chlorite-iodide. This is the fundamental or minimal chlorite-iodine oscillator in that it contains the minimal set of reactants necessary to generate processes (M 1)-(M 3). 

A ) Chlorite-iodide-iodate. While this system fits into either categories B) or C) below, it may also be considered a sort of fundamental oscillator which is generated (via M4, M8 or M9) by the systems of type B) or C). 

B) Chlorite-iodide-oxidant. These systems are represented by oscillators 2,4,5 and 6 in Table 8. They are identified by the fact that they exhibit oscillations over a significantly broader range of constraints than the fundamental CIOJ-I- subsystem. The chief requirements on the substrate Ox are that (M4) be thermodynamically favorable (Eox/Red > 0-54 V) and rapid, (though not faster than (M2) + (M3)) and that... 

M7) be slow in some accessible range of pH and reactant fluxes. One oxidant which fails to enhance the range of constraints over which a chlorite-iodide system will oscillate is peroxydisulfate. In spite of its highly favorable reduction potential (E° = 2.01 V), S2Og reacts too slowly with I" in reaction (M4) to be a useful oscillatory substrate. 

C ) Chlorite-iodate-reductant. Oscillators 2, 7, 8 a, 9 a, 10 a, 11 and 12 of Table 8 are of this type. The requirements for a successful substrate appear to be that (M8) be thermodynamically favorable and relatively rapid while (M10) is slow. 

C") Chlorite-iodine-reductant. These systems, which include systems 8 b, 9 b and 10b of Table 8 appear to be only minor variants of type C ) in which (M 9) replaces (M 8). C ") Chlorite-iodide-reductant. The only known example of this type is the chlorite-iodide-malonic acid system, which is of special interest because it supports both batch oscillations and spatial wave patterns. The slow decomposition of iodinated malonic acid species apparently provides a long lasting, indirect flux of iodide (via (M2) + (M9)) in this system. 

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. 

While no complete mechanism has yet been developed which predicts oscillation in a chlorite oscillator from the integration of a set of rate equations derived from elementary... 

In this article an attempt is made to include some new contributions to bring the field of oscillations in the dynamics of chemical reactions up to date. To provide a continuation, the basic structure of the paper follows the outline of the previous article which will be referred to as (G G). Moreover, some recent studies have also been added to the field, and they are included as additional sections. These new sections are L. Oxidation by Chlorite M. Miscellaneous Studies and N. General Models and Mathematical Techniques. 

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