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 studied in a W/O microemulsion (Water/AOT/Heptane at different [Water]/[Amphiphile] mole ratios) and in mixed water-organic media (water-formamide, water-ethylene glycol, and water-dioxane). The pseudo-first-order rate constants were observed to radically increase in microemulsion media 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 water. At a constant mole ratio, the rate constant was witnessed to be independent of [AOT]. In all mixed media, the rate decreased with increasing proportion of the nonaqueous solvent. The ionic-strength effect on the reaction did not obey either the modified Bronsted-Bjerrum or Bronsted-Bjerrum-Pitzer relations in the studied nonaqueous media, except for ethylene glycol. This disagreement is very prominent in the studied W/O microemulsion medium at [Water]/[AOT] omega = 9.1. The activation parameters for the pseudo-first-order reaction in all of the studied 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.