Electron transfer reactions between the superoxide ion and quinones

The electron transfer reactions of the superoxide ion with benzoquinone, trimethylbenzoquinone, and menadione in dimethylformamide were studied. A procedure of the determination of the relative rate constants of these reactions was developed; the reaction of O 2 with butyl bromide was chosen as a standard one. The relative rate constants measured at 20,°, 35°, and 50°C were slightly dependent on the quinone structure. The relationship between the free energy Δ F *of the electron transfer reactions and the standard free energy Δ F o was discussed. This relationship is proposed as Δ F * = αΔ F o + β, where the proportionality coefficient α is equal to 0.04–0.11 for exothermal reactions and to 0.90–0.96 for endothermal reactions.