On the origin of electrochemical oscillations in the picric acid/CTAB two-phase system

The oscillatory picric acid/CTAB two-phase system-as introduced by Yoshikaw a and Matsubara [J. Am. Chem. Soc. 1984, 106, 4423-4427]-has been revisited . UV-vis spectroscopic studies were presented that provide a clearer and ne w insight into the possible kinetic mechanism for the oscillatory behavior. It was shown that the key process in the system is the formation of 1: 1 i on pairs between picrate and CTA(+) at the liquid/liquid interface that des orb and move into the organic phase. Kinetic UV-vis experiments also showed that the presence of alcohol-which was essential to observe oscillatory be havior-inhibits the formation of ion pairs. In the course of this process, this inhibition is released presumably due to the transfer of the alcohol f rom the interface into the organic phase. The corresponding inhibition/acce leration dynamics were observed in a subsystem experiment as S-shaped, auto catalytic -like kinetics with respect to the ion-pair formation. A new mech anism based on Langmuir-Hinshelwood kinetics was proposed that includes the competitive adsorption of CTA(+), picrate, and the alcohol at the liquid/l iquid interface. The release of inhibition, which depends on the concentrat ion of vacant interface sites and which occurs autocatalytically, expresses the key process for the nonlinear behavior. Computer simulations were perf ormed which confirm that the proposed kinetic mechanism is dynamically reas onable.