Kinetics and mechanism of the oxidation of diaquabis(1,10-phenanthroline) iron(II) by periodate in aqueous and micellar media

Abstract

The kinetics of oxidation of [FeII(phen)2(H2O)2]2+ (phen = 1,10-phenanthroline) by periodate were investigated in aqueous acidic medium at different [H+] over a temperature range of 20–40 °C. The reaction was studied under pseudo-first-order conditions by taking [IO 4 − ] > tenfold over [FeII(phen)2(H2O) 2 2+ ]. The reaction rate increases with increasing [H+], and the kinetics of oxidation obeyed the following rate law: $$ {\text{Rate}} = \left[ {{\text{Fe}}^{\text{II}} ({\text{phen}})_2({\text{H}}_{2} {\text{O}})_{2}^{2 + } } \right]\left[ {{\text{IO}}_{4}^{ - } } \right]\left\{ {k_{4} K_{2} + k_{5} K_{1} K_{3} [{\text{H}}^{ + } ]} \right\} $$ The surfactant sodium dodecyl sulfate was found to enhance the rate, whereas cetyltrimethylammonium bromide had little effect. Activation parameters associated with k 2 and k 3 were calculated. An electron transfer from Fe(II) to I(VII) is identified as the rate-determining step. The I(VI) species thus generated reacts in a fast step with another Fe(II) complex.