COUNTERION CONTROL OF REACTIVITY IN ANIONIC REVERSE MICELLAR AGGREGATES

The sodium counterion of the surfactant AOT (sodium bis-(2-ethylhexyl) sulfosuccinate) has been replaced by calcium, magnesium, zinc and aluminum ions. In reverse micellar aggregates of these surfactants in heptane, acidity induced by these cations, at low water content, is revealed by an acid-sensitive optical probe (2′,7′-dichlorofluorescein). The magnitude of this effect parallels the hydrolysis rate of triethylorthobenzoate. A strong catalytic effect is observed with zinc and aluminum counterions. The acidity effect of the counterions follows the order: Na+ < Ca 2+ ≈ Mg2+ < Zn2+ < Al3+. © 1990.