Kinetic Studies of the Electron Transfer Reaction in Iron(II) and Iron(III) Systems. VI. Reaction in N,N-Dimethylformamide

Abstract

Abstract The electron transfer reaction between Fe(II) and Fe(III) in N,N-dimethylformamide (DMF) was found to be influenced by the presence of perchloric acid, chloride ion, and water in the reaction system. This suggests that the reaction involves chemical species such as partially hydrated iron, its deprotonated iron, and FeCl2+ and FeCl2+. The individual rate constants in DMF, containing a small amount of water, are k0=33.6 M−1s−1 for Fe2+–Fe3+, k1=1.2×102 M−1s-−1 for Fe2+–FeCl2+, and k2=∼103 M−1s−1 for Fe2+–FeCl2+ at μ=0.20 M and 25°C. The formation constant for FeCl2+ was determined to be K1=(2.0±0.3)×104 M−1 at μ=0.20 M and 25°C. In the mixed solvents of DMF and water, the apparent rate constant exhibited a minimum at a certain water concentration. The activation parameters for the reactions Fe2+–Fe3+ and Fe2+–FeCl2+ are ΔH0\eweq=8.3 kcal/mol, ΔS0\eweq=−24 cal/deg·mol, ΔH1\eweq=4.5 kcal/mol, and ΔS1\eweq=−34 cal/deg·mol, respectively. The results are compared with those in H2O, D2O, and DMSO.