Oscillating reactions Landolt

Two reportshave appeared recently on the Landolt oscillating reaction. Where the oxidation of sulfite and ferrocyanide by iodate takes place in a continuously stirred reaction vessel, large-amplitude oscillations in pH at constant [I ] are observed. The nature of the intermediates and elementary steps have been discussed together with the detailed mechanistic profile. The overall processes may be described as shown in equations (31)-(37). Individual rate constants for the rate-determining steps in the above reactions have been identified. 

The system used in the Landolt clock reaction, IOj/SOl , when treated with [Fe(CN)6] , shows oscillations in a CSTR. A modification of the mechanism proposed previously resolves a number of problems. A slightly different system, I03/HS03/S20i produces a small number of high-amplitude pH oscillations (up to 2 units of pH) over a narrow range of conditions in a closed system. ... 

A Landolt pH-oscillator based on a bromate/sulfite/ferrocyanide reaction has been developed with a room temperature period of 20 minutes and a range of 3.1periodic oscillations in volume in a pH responsive hydrogel. A continuously stirred, constant volume, tank reactor was set-up in conjuction with a modified JKR experiment and is used to show that the combination of a pH oscillator and a pH responsive hydrogel can be used to generate measurable force. 

An elegant example of the empirical rate law approach is the model developed by Gaspar and Showalter (1990) for the mixed Landolt or Edblom-Orbdn-Epstein (EOE) reaction (Edblom et ah, 1986). The reaction of iodate, sulfite, and ferrocyanide ions in a CSTR gives rise to sustained oscillation. In a flow reactor, the concentrations of two of these input reactants -iodate and ferrocyanide—remain nearly constant, while the pH and the concentrations of sulfite. 

Edblom, E. C. Orban, M. Epstein, I. R. 1986. A New lodate Oscillator The Landolt Reaction with Ferrocyanide in a CSTR, J. Am. Chem. Soc. 108, 2826-2830. Edelson, D. Allara, D. L. 1980. A Computational Analysis of the Alkane Pyrolysis Mechanism Sensitivity Analysis of Individual Reaction Steps, Int. J. Chem. Kinet. 12, 605-621. 

While no confirmed reports of new iodate oscillators have yet appeared, it seems inevitable that systems based on the bistable arsenite-iodate [30,31] or related Landolt-type [32] reactions will soon be made to oscillate. The iodide-peroxydisulfate-oxalate reaction discussed by Chopin-Dumas elsewhere in this volume may be the first of the new iodate oscillators. 

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