Bromate-chlorite-iodide reaction

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). 

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

Figure 7.5 Simulation of the bromate-chlorite-iodide reaction, (a) With an error tolerance of lO", chaotic behavior is obtained, (b) Tightening the tolerance to 10" leads to the correct result, periodic behavior. (Adapted from Citri and Epstein, 1988.)...

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.)...

To what extent are we justified in thinking of a chemically coupled oscillator system as consisting of the two independent subsystems plus a set of cross-reactions that provide the coupling A partial answer can be found in a mechanistic investigation of the bromate-chlorite-iodide reaction (Citri and Epstein, 1988). The mechanisms that had been derived for the bromate-iodide and chlorite-iodide systems in independent studies of these reactions are shown, respectively, in Tables 12.1 and 12.2. 

Figure 12.5 Phase diagram of the bromate-chlorite-iodide system calculated using the mechanism in Table 12.3. Fixed constraints and symbols as in Figure 12.3. C signifies compound oscillation, C, signifies one compound oscillation plus j chlorite-iodide oscillations per cycle, (Reprinted with permission from Citri, O. Epstein, I. R. 1988. Mechanistic Study of a Coupled Chemical Oscillator The Bromate-Chlorite-Iodide Reaction, J. Phys. Chem. 92, 1865-1871. 1988 American Chemical Society.)...

Figure 12.16 Experimentally observed compound oscillation in the bromate-chlorite-iodide reaction, [I ]q = 4 x 10 M, other constraints as in Figure 12.3. (Adapted from Alamgir and Epstein, 1983.)...

Citri, O. Epstein, I. R. 1988, Mechanistic Study of a Coupled Chemical Oscillator The Bromate-Chlorite-Iodide Reaction, J. Phys. Chem. 92, 1865-1871. 

Table I. Mechanism of the Bromate-Chlorite-Iodide Oscillating Reaction...

Chemically coupled oscillators can also give rise to chaotic behavior. Again, we choose an example from the bromate-chlorite-iodide system. Although this system may well show isolated regions of chaos, the best characterized chaotic behavior in this reaction occurs as part of a period-adding sequence in which, as the... 

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... 

The chlorite family contains several subfamilies, most notably the iodate, iodide, and bromate branches. Several oscillators—for example, the chlorite-bro-mate-iodide reaction constitute links between subfamilies, with a foot in each camp. 

With the single exception of the chlorite-bromate-reductant systems [14], for which a mechanism has been developed by joining the NFT model [26] with THOMPSON S [42] mechanism for the BrOj -ClOo reaction, no mechanism has been published for any chlorite oscillator. In Table 2, we give a recently developed mechanism [43] for the minimal chlorite-iodide oscillator. Of special significance is the fact that it contains no radical species, but rather the binuclear intermediate CIO,. Calculations with this mechanism give excellent agreement with a wide variety of experimental results. One example is given in Fig. 5. 

The first system on which this approach was tried (De Kepper, Epstein and Kustin, [ 18]) employed two coupled autocatalytic reactions, chlorite plus iodide, and arsenite plus iodate, which have key intermediates in common. As Figure h shows, the chlorite-iodate-arsenite system did indeed prove to oscillate, constituting the first systematically designed chemical oscillator. More recently, by starting from the fundamental or minimal chlorite-iodide bistable system and adding different feedback species, it has been possible to generate a family of nearly 20 different chlorite-iodine species oscillators (Orb n et al., [19]). In addition, two iodine free chlorite oscillators involving thiosulfate (Orban, De Kepper and Epstein, [ 20] ) and bromate (Orban and Epstein, [21]) have been found. 

The latest postcolumn derivatization method for the analysis of disinfection by-product anions such as bromate and chlorite has been published as Method 326.0 by the US EPA [68,69]. This method was developed as an alternative to Method 317.0, because o-dianisidine has been identified as a potential human carcinogen [70]. Method 326.0 uses a postcolumn reaction that generates hydro-iodic acid (HI) in situ, from an excess of potassium iodide that combines with bromate from the column effluent to form the tri-iodide anion, I3. The reaction product can then be detected photometrically at 352 nm. Most published EPA... 

Following the proposed method of Weinberg and Yamada, SahU and von Gunten [63] developed a derivatization technique for the determination of bromate, iodate, chlorite, and nitrite that generates hydroiodic acid (HI) in situ from potassium iodide. The reaction scheme for bromate is as follows ... 

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