Iogannsen M G, Petrov A S, Kachurin A M
Vopr Med Khim. 1993 Jan-Feb;39(1):9-13.
Oxidation of amidopyrine, analgin and 4-aminoantipyrine by means of H2O2 was studied in presence of peroxidase and hemoglobin. As shown by NMR, EPR and spectrophotometry the oxidation was of single electron type accompanied by free radical formation. The radicals of amidopyrine and analgin were stable, colored, participated in chemical exchange with initial molecules and disproportionated as demonstrated by stoichiometry. Radicals of 4-aminoantipyrine were unstable and dimerized to antipyrine red. Aminopyrazolone radicals were also formed after direct oxidation by Fe3+ in acidified water containing no complexes. The Fe-complexes developed shifted the equilibrium towards reduction of radicals with formation of the initial molecules. Presence of 4-amino groups was responsible for oxidation of pyrazolones under mild conditions. Alkyl derivatives of 4-amino group protons stabilized the radicals and altered their subsequent transformation form dimerization to disproportionation. Proton catalysis of aminopyrazolone oxidation occurred.
