Kinetic Studies of the Electron Transfer Reactions in Iron(II) and Iron(III) Systems. IX. Electron Transfer Reactions between Iron(II) and Iron(III) in Water Mixed with Ethanol, 1-Propanol, Ethylene Glycol, Glycerol, and Pentaerythritol

Abstract

Abstract The rate constants of the electron transfer reactions between Fe(II) and Fe(III) were determined in mixed solvents of water and alcohols, such as ethanol, 1-propanol, ethylene glycol, glycerol, and pentaerythritol. From the acid concentration dependence of the rate, the predominant path of the reaction was estimated to be Fe2+-Fe(OH)2+ path with a rate constant kH. The rate constant kH increases with increase in the mole fraction x of ethanol and 1-propanol, and decreases with increase in x of methanol, ethylene glycol, glycerol, and pentaerythritol. A straight line is obtained when In kH is plotted against the reciprocal dielectric constant D−1 of the mixed solvents for the latter group of alcohols. From the slope of the straight line the distance between Fe2+ and Fe(OH)2+ is estimated to be 7.8 Å at the intermediate stage of the reaction. Therefore, the reaction is mostly controlled by the electrostatic repulsive force, being influenced by D of the mixed solvents.