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 ([H2O]/[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. (c) 2005