Electron spin resonance study of the reaction of SO4˙– with azolinones

Abstract

The reactions of photolytically generated sulfate radical-anion, SO₄˙^–, with several nitrogen-containing heterocycles of the azolinone type in aqueous solutions were studied by ESR spectroscopy. SO₄˙^– reacts by formal hydrogen abstraction from an NH group to yield neutral radicals in acidic and neutral solutions and the respective radical-anions at basic pH. The pK_a-values of radicals derived from 2,3-dihydroimidazol-2(1H)-one, 2-oxo-2,3-dihydro-1H imidazole-4-carboxylic acid and 2,3-dihydroindazol-3(1H)-one were determined to be in the range 8.5–10.4. In the cases of 2,3-dihydroimidazol-2(1H)-one and 2,3-dihydropyrazol-3(1H)-one secondary radicals were detected at basic pH. These radicals resulted from the disproportionation of the primary radicals followed by addition of OH^– and oxidation of the OH-adduct.