Kinetics and electrochemical studies on superoxide

Rate constants for the reaction of superoxide O-2 with various substrates were obtained through stationary electrode polarography theory and technique. In solvent acetonitrile, the substrate and the rate constants of the reaction O-2 + AH-k2→Product, are, AH = isopropanol (k2 < 0.01 M-1 s-1); ethanol (k2 = 1.42 × 102 M-1 s-1); methanol (k2 = 1.1 × 107 M-1 s-1), H2O (k2 = 1.0 × 105 M-1 s-1). In MeCN, O-2 was found to be rather unreactive towards glucose and acetone but it reacts with fructose and sucrose catalytically. However, in DMF2, O-2reacts with glucose and fructose with k2 order of 105 M-1 s-1. The mechanism of the reaction of O-2 with the substrates (AH) is proposed as O-3 + AH k2O, AHk2k-1 k′ [O2H + AH]-, k-2→O2H + A- with k1 = 109 M-1 s-1 and k-1 = 108 -109 s-1. With these values of k-1 and k1, k′ k2(obs). The reversible E1/2 for O2 + e O-2 in various solvents: MeCN, acetone, isopropanol, methanol, H2O were obtained either directly from the reversible voltammogram or from experimental voltammograms and the rate constants obtained (as above) using stationary electrode polargraphy theory; E1/2 being -0.82 (MeCN),-0.85 (acetone),-0.72 (isopropanol);-0.66 (MeOH),-0.56 (H2O) vs SCE.