Kinetics of dissociation of tris-(2,2′-bipyridyl) iron(II) in water solubilized by Triton X-100 reverse micelles

Abstract

The dissociation of tris-(2,2′-bipyridyl) iron(II) ([Fe(bipy) 3] 2+) has been studied in the Triton X-100/hexanol/cyclohexane reverse micellar medium. The reaction obeys simple first-order kinetics with no evidence of autoinhibition. The first-order rate constant ( k 1 ) has been determined at different values of W ([H 2O]/[Triton X-100]). The rate ( k 1 ) decreases with increasing value of W. k 1 also increases with increase in Triton X-100 concentration at constant values of W, showing that the reaction takes place at greater speed at the micellar interface. The kinetic results can be interpreted by the monomolecular pseudo-phase model. The effect of W on rate ( k 1 ) is more pronounced in the range of W from 1.55 to 4.2 but less pronounced at higher W. The reaction is further accelerated by Cl − and SCN − ions and the kinetic results provide evidence for the formation of ion pairs between the cation [Fe(bipy) 3] 2+ and each of these anions. The formation of such ion pairs has not been observed in aqueous medium but has been reported earlier in aqueous–alcohol mixtures. This result therefore provides evidence for the lower micropolarity of solubilized water compared to ordinary water.