Abstract
Rate enhancements of the Ni2+–PADA bidentate formation reaction have been obtained at 25.0 °C in anionic micellar solutions with added electrolyte. Sodium dodecylsulfate, sodium octanesulfonate, and sodium octylsulfate were the surfactants employed and Na+, Ca2+, and Mg2+ were the added cations. Kinetic analyses revealed that the chief effect in leading to a decreased rate enhancement with salt present was a lowering of the surface potential manifested by an increase in the reaction volume. The binding of the Ni2+ ion to the micelles showed little change beyond an initial drop with the lowest Na+ addition with sodium dodecylsulfate. The binding of the hydrophobic reagent PADA decreased more gradually but not sufficiently to account for the reduction in rate enhancements. In the presence of Ca2+ or Mg2+ ions, the rate enhancements and the kinetic parameters did not show unusual behaviour except that Mg2+ ion appeared to be slightly more effective in excluding Ni2+ ion from the micellar surface region. The sphere-to-rod micellar transformation that occurs at 0.4 mol dm−3 Na+ does not have a pronounced effect on the micellar surface region.
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