Benzaldehyde oscillating oxidation

The actual schemes of these reactions are very complicated the radicals involved may also react with the metal ions in the system, the hydroperoxide decomposition may also be catalysed by the metal complexes, which adds to the complexity of the autoxidation reactions. Some reactions, such as the cobalt catalysed oxidation of benzaldehyde have been found to be oscillating reactions under certain conditions [48],... 

Mittal, et al. (1981) reported a new reaction which consists of uncatalyzed acidic bromate oxidation of 3,4-dimethoxy benzaldehyde resulting in oscillations in redox potential. Recently, Nair, et al. (1982) reported the oscillating behavior in the uncatalyzed aqueous acidic bromate oxidation of 3,4-dimethoxy benzaldehyde. 

Thus, it is well established that deterministic chaos plays a role in chemistry. It has been analyzed in different chemical processes. Asked about the importance of chemical oscillations and chaos in the chemistry of mass industrial production, Wasserman, former director of research at Dupont de Nemours and past-president of the American Chemical Society in 1999, said [15] "Fes. The new tools of nonlinear dynamics have allowed us a fresh viewpoint on reactions of interest". Ehipont has identified chaotic phenomena in reactions as important as the conversion of the p-xylol in terephtalic acid or the oxidation of the benzaldehyde in benzoic acid. 

Aerial oxidation of Aldehydes Chemical oscillations have been noted in a system consisting of benzaldehyde, acetaldehyde, sodium bromide, cobalt (II) acetate and nitric acid. When air is passed through the reaction mixture at 70°C, colour of the solution oscillates between pink and dark brown. The system is quite suitable for classroom demonstration. If a platinum electrode is inserted in the medium and is coupled to a calomel electrode, changes in redox potential are observed which is synchronized with the colour changes [16, 17] (Figs. 9.5 and 9.6). 

Figure 9.5. Reaction ceU used for monitoring oscillations in colour during oxidation of benzaldehyde P = Photocell, Q = Condenser, T = Thermometer, S = OsciUatoiy solution, A = Coming glass cell, L = Light source, Dj, D2 = Dimmerstat, C2 = Compressor, H = Hot plate, R = Recorder or Digital multimeter.

Interest in benzaldehyde oxidation has recently been revived by the observation of oscillations [23,24] and propagating reaction fronts [25-27] due to its autocatalytic nature. 

During the oxygen or air oxidation of benzaldehyde catalyzed by cobalt and bromide several measureable parameters oscillate including redox potential, absorbance at 620 nm, oxygen concentration, rate of benzaldehyde disappearance and free radical concentration. At 55-100°C in a 90/10 acetic acid/water mixture the oscillations will last for many hours[l]. A typical cycle is shown in Figure 1. 

New Chemical Oscillators (plenary lecture). By I.R. Epstein (With 9 Figures) 24 The Mechanism of the Oscillating Air Oxidation of Benzaldehyde... 

To the author s knowledge, with the exception of the benzaldehyde autoxidation oscillating reaction and the methylene blue catalyzed oxidation of sulfide by oxygen, all the new chemical oscillators discovered since 1980 are the result of the bistability-oscillation approach. This shows that, if bistability (or pleated slow manifold) is not of basic necessity for oscillatory behaviour, our method which realies on some particular type of relationship between bistability and relaxation oscillations, is presently the most efficient method to produce new chemical oscillators. 

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