ELECTRON-SPIN-RESONANCE STUDY OF THE REACTION OF SO4-CENTER-DOT- WITHAZOLINONES

The reactions of photolytically generated sulfate radical-anion, SO4.- with several nitrogen-containing heterocycles of the azolinone type i n 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(2)-values of radicals derived from 2,3-dihydroimidazo l-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.