Kinetic Studies of the Electron Transfer Reactions in Iron(II) and Iron(III) Systems. XI. Electron Transfer Reaction between Aquairon(II) and Tris(1,10-phenanthroline)iron(III) in Water Mixed with Methanol, Ethanol, 1-Propanol, and Ethylene Glycol

The electron transfer reaction Fe2+aq+Fe(phen)33+→Fe3+aq+Fe(phen)32+ has been investigated in order to find out the influence of the dielectric nature of media on the reaction rates, by the method of stopped-flow spectrophotometry. As the reaction media, were used aqueous mixtures with various alcohols, such as methanol, ethanol, 1-propanol, and ethylene glycol at their various mole fractions x. The second-order rate constant k grows larger approximately linearly with the increase in x, in a sequence: methanol<ethylene glycol1-propanol. When In k is plotted against D−1 (the reciprocal dielectric constant), all points come together on a single straight line with a positive slope, indifferent to the kinds of the alcohols used. This fact suggests that the reaction proceeds through three successive elementary processes, Fe2+aq+Fe(phen)33+\overseti→[Fe(H2O)62+·Fe(phen)33+]\oversetii→[Fe(H2O)63+·Fe(phen)32+]\oversetiii→Fe3+aq+Fe(phen)32+, in which Process i is the formation of an outer-sphere ion-pair ...