Electron spin resonance and pulse radiolysis studies on the reaction of OH sup sm bullet and SO sub 4 sup sm bullet minus with five-membered heterocyclic compounds in aqueous solution

The reactions of several five-membered oxygen and nitrogen heterocyclics with OH • and SO 4 •− radicals have been investigated in aqueous solution using in-situ radiolysis and photolysis ESR, and optical and conductometric pulse radiolysis techniques for detection. OH . reacts with (the saturated) oxazolidone, imidazolidinone, hydantoin, and oxazoline derivatives by hydrogen abstraction, preferentially from the carbon adjacent to the nitrogen atom. With (the unsaturated) oxazoles and isoxazoles, OH • reacts by addition to the carbon at the 5-position of the ring to produce allylic radicals. In basic and acidic solutions of oxazole a ring opening process follows the OH • addition. SO 4 •− reacts with oxazoles and isoxazoles by addition to C5 yielding SO 4 − adducts, whereas with imidazole, pyrazole, and pyrrole derivatives, SO 4 •− gives rise to neutral, conjugated radicals with the unpaired electron delocalized over the entire ring, which are derived from the parent compounds by one-electron oxidation followed by deprotonation