ELECTRODE-REACTIONS OF NITROXIDE RADICALS .9. ANODIC OXIDATIONS OF 4-HYDROXYIMINO-2,2,6,6-TETRAMETHYLPIPERIDINE-1-OXYL AND 4-[(AMINOCARBONYL)-HYDRAZONE]-2,2,6,6-TETRAMETHYLPIPERIDINE-1-OXYL IN WATER SOLUTIONS

Anodic reactions of two stable nitroxide radicals, 4-hydroxyimino-2,2,6,6-tetramethypiperidine-1-oxyl (1) and 4-[(aminocarbonyl)-hydrazone]-2,2,6,6-tetramethylpiperidine-1-oxyl (2) were studied in aqueous solutions over the pH range 5.33-8.04 using the cyclic voltammetry technique. They show one-electron oxidation processes of reversible and quasi-reversible natures, depending on scan rate conditions at pH 5.33. The diffusion coefficients, the observed standard rate constants (k(s)), and the oxidation potentials for the redox reaction nitroxyl radical reversible oxoammonium salt have been determined. A one-electron transfer process, followed by an irreversible chemical reaction, is observed at pH greater-than-or-equal-to 5.71, and the rates of this reaction at pH 5.71 and 6.71 are 0.11 and 0.080 s-1, respectively. Controlled-potential electrolysis at 0.8 V (vs. SCE) confirms a one-electron electrode reaction.