Micellar Effects on the Kinetics of Cerium(IV) Oxidation and the Cerium(IV)-Catalyzed Belousov−Zhabotinsky Reaction with Methyl-, Ethyl-, or Benzylmalonic Acid

Abstract

The kinetics of the oxidation of methyl- (MeMA), ethyl- (EtMA), or benzylmalonic (BzMA) acid by ceric ions and the Ce(IV)-catalyzed Belousov−Zhabotinsky (BZ) reaction with these substrates have been studied at 20.0 °C in stirred batch conditions in the absence and the presence of the cationic surfactant cetyltrimethylammonium nitrate (CTAN). Some measurements have also been performed using the anionic surfactant sodium dodecyl sulfate (SDS). Addition of increasing amounts of CTAN has a little inhibitory influence on the redox process with MeMA and EtMA, whereas it causes a significant enhancement with BzMA. Small decreasing rate effects are observed in the presence of SDS. In the absence of surfactants, the BZ systems with MeMA and EtMA show oscillatory behavior after an induction period, whereas no oscillations are found with BzMA. In the presence of CTAN all the systems exhibit oscillations after an induction period that is shortened markedly with increasing CTAN concentration and that, at constant [CTAN], increases in the order BzMA < MeMA < EtMA. Added CTAN also affects the oscillation period and the duration of the raising portion of an oscillatory cycle. The surfactant SDS affects these oscillatory parameters to a different extent. Explanations of the experimental results are provided.