REACTION-KINETICS IN A MICROEMULSION MEDIUM .4. HEXACYANOFERRATE(III)-IODIDE REACTION IN WATER AEROSOL-OT/HEPTANE MICROEMULSION AND MIXED-SOLVENTS/

The kinetics of the reaction between [Fe(CN)(6)](3-) and I- was studie d in a W/O microemulsion (Water/AOT/Heptane at different [Water]/[Amph iphile] mole ratios) and in mixed water-organic media (water-formamide , water-ethylene glycol, and water-dioxane). The pseudo-first-order ra te constants were observed to radically increase in microemulsion medi a with a [Water]/[AOT] mole ratio below 6. At a mole ratio of 5.4, the rate constant was found to be about 20-fold greater than that in wate r. At a constant mole ratio, the rate constant was witnessed to be ind ependent of [AOT]. In all mixed media, the rate decreased with increas ing proportion of the nonaqueous solvent. The ionic-strength effect on the reaction did not obey either the modified Bronsted-Bjerrum or Bro nsted-Bjerrum-Pitzer relations in the studied nonaqueous media, except for ethylene glycol. This disagreement is very prominent in the studi ed W/O microemulsion medium at [Water]/[AOT] omega = 9.1. The activati on parameters for the pseudo-first-order reaction in all of the studie d media suggested distinct difference of the microemulsion from other solvents. A reasonable compensation between Delta H-double dagger and Delta S-double dagger i.e., the isokinetic effect, was observed.