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Abstract

Results concerning the effect of salicylic acid on the Briggs-Rauscher oscillating reaction in batch mode are presented. In contrast to the other phenolic and polyphenolic compounds studied before, this compound does not stop immediately the oscillations; however it reduces the amplitudes gradually. The time elapsed between the addition of the salicylic acid and the complete cessation of the oscillations is denominated as attenuation time. After the inhibition time the oscillations are restarted with low amplitude. The dependence of the amplitudes, attenuation time, inhibition time and period times on the salicylic acid is presented. Furthermore a new method for kinetic study of the unusual inhibitory effect is implemented. The reaction was followed potentiometrically, by means of an iodide ion selective electrode coupled to a double junction saturated calomel electrode. We derived the integrated rate equation that corresponds to the pseudo-first order reaction followed by a sensor with a nernstian transfer function. The hypothesis concerning the pseudo-first order kinetics of iodide ion production and consumption over a relatively long time within one period of oscillation is proven. The rate constants of iodide ion production and consumption are diminished gradually for the oscillations after the addition of salicylic acid. The fact that salicylic acid decreases the amplitudes and the rate constants of iodide ion formation and consumption during the attenuation period lead to the conclusion that this compound manifests a weak inhibitory effect in the attenuation period as well. However this inhibitory effect increases in time, until complete cessation of the oscillations.