PH Dependence of the Belousov−Zhabotinsky Reaction in Water-in-Oil Reverse Microemulsion of AOT in Octane

Abstract

The ferroin-catalyzed Belousov−Zhabotinsky reaction in water-in-oil microemulsion with anionic surfactant Aerosol OT exhibits chemical oscillations in spite of its extremely high pH in the aqueous pseudophase. In order to elucidate the reaction mechanism, we have measured the rate of autocatalytic step in the inorganic subset of the reaction under the batch conditions. We have found that the rate depends linearly on the concentration of H2SO4 and quadratically on the concentration of NaBrO3, in contrast to the dependence in the homogeneous aqueous solution in which both dependences are linear. The rate constant was found to be an order of magnitude higher in the microemulsion than that in the homogeneous aqueous solution. It is suggested that a possible increase in pKa of HBrO3 in the reverse micelles requires a modified reaction scheme, which accounts for the observed dependency and explains why chemical oscillations can be observed in reverse micelles under unusually high-pH conditions.