title: One-electron redox reactions of pyrazolin-5-ones. A pulse radiolysis study of antipyrine and analogues.
abstract: One-electron oxidation of several derivatives of pyrazolin-5-one, including the drug antipyrine, were studied by pulse radiolysis of aqueous solutions. All the compounds were found to be oxidized by Br2 rapidly (k approximately 3 X 10(8)-2 X 10(9) M-1 s-1) but considerably more slowly by weaker oxidants, such as peroxyl radicals. From redox equilibria using p-methoxyphenol and N,N,N',N'-tetramethyl-p-phenylenediamine as reference compounds, the one-electron oxidation potentials of the methyl-substituted 2-pyrazolin-5-ones were found to be in the range of 0.32-0.39 V versus normal hydrogen electrode. The relevance of these findings to the properties of the drug nafazatrom is discussed. Antipyrine was found to have a much higher oxidation potential, estimated as 1.2-1.5 V, which is rationalized on the basis of the phenyl substitution and lack of resonance stabilization of the radical cation.
mesh_terms: D000983:Antipyrine / Q000528:radiation effects*; D001965:Bromides; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D011720:Pyrazoles / Q000528:radiation effects*; D013057:Spectrum Analysis; D013329:Structure-Activity Relationship
chemical_list: D001965:Bromides; D011720:Pyrazoles; D000983:Antipyrine