Chlorite-iodine-malonic acid reaction

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 ... 

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

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 . 

Operated in a CSTR, the CIMA reaction produces, as a function of iodide or chlorite feed concentrations, bistability between an iodine reduced state (high iodine, high iodide concentration) and an iodine oxidized state (low iodide concentration) at relatively low malonic acid feed concentration. Sustained oscillations are produced at higher concentration [14,59]. Using starch as iodine color indicator, the reduced state colors daric blue while the oxidized state is clear or pale yellow. 

We first found that a simple extension of the most widely used model of the chlorite-iodide reaction [35] to include the malonic acid-iodine reaction cannot account for the oscillation in batch. One or more essential species and their reactions, which are negligible at the concentrations used in the CSTR, must be important in batch. Earlier mechanistic studies did not consider the formation of CIO2 in the chlorite-iodide reaction. The possible role of the... 

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