Catalysis by AOT reverse micelles <img src='/image/spc_char/dash.gif' border=0> Kinetics of aquation of bis(2,4,6–tripyridyl- s-triazine)iron(II) and acid hydrolysis of 2,2′,6,6′′ terpyridyl iron(II) in the presence of AOT/heptane

Abstract

The kinetic study of the aquation of bis(2,4,6–tripyridyl-s-triazine)iron(II), {Fe(tptz)₂}²⁺ and acid hydrolysis of 2,2′,6,6′′ terpyridyl iron(II), {Fe(terpy)₂}²⁺ have been carried out in the presence of water pools of AOT/heptane reverse micelles. The aquation of {Fe(tptz)₂}²⁺ is markedly accelerated in the presence of AOT/heptane reverse micelles compared to aqueous medium. The significant increase in rate is attributed to the special properties of the water pool-like high nucleophilicity of water, low dielectric constant and favourable partitioning of tptz ligand into the organic phase. The rate of the reaction increases with increase in [H₂O] at constant [AOT] and decreases linearly with increase in [AOT] at constant [H₂O]. The dependence of the aquation rate on water concentration has been used in elucidating the role of water in the rate determining step. In the acid hydrolysis of {Fe(terpy)₂}²⁺ the reaction proceeds with a rate constant <i>k</i>′= 11.2×10^-4 s^-1 in the presence of AOT/heptanes while the reaction is extremely slow and incomplete under identical conditions in aqueous medium. Higher rate observed in reverse micelles is attributed to low dielectric conditions in the water pool. The study has been carried out at different <i>W </i>values and at different surfactant concentrations (<i>W </i>= [H₂O]/[surfactant])<i>.</i> The effect of surfactant concentration has been explained on the basis of Berezin pseudo phase model.