FORMATION OF RADICAL-ANIONS ON THE REDUCTION OF CARBONYL-CONTAINING PERFLUOROAROMATIC COMPOUNDS IN AQUEOUS-SOLUTION - A PULSE-RADIOLYSIS STUDY

Radical anions are formed on addition of hydrated electrons to pentafl uoroacetsphenone (PFA) and pentafluorobenzaldehyde (PFB) in aqueous so lutions. On the other hand, addition of hydrated electrons to pentaflu orobenzoic acid (PFBA) leads to rapid fluoride elimination. The spectr um of the radical anion of PFA has lambda(max) at 300 and 440 nm with absorption coefficient at 440 nm epsilon(440) = 2100 L mol(-1) cm(-1). PFA(.-) decays with a rate constant of (7 +/- 3.0) x 10(3) s(-1). It has a pK(a) = 7.5 and the spectrum of the conjugate acid has lambda(ma x) at 270 and 460 nm with epsilon(460) = 900 L mol(-1) cm(-1). The spe ctrum of the radical anion of PFB has lambda(max) at 285 and 430 nm wi th epsilon(430) = 800 L mol(-1) cm(-1). PFB.- decays with a rate of (4 +/- 2) x 10(3) s(-1). It has a pK(a) = 7.2 and the spectrum of the co njugate acid has weak absorption at 330 nm. Evidence for the formation of the radical anion was obtained from intermolecular electron transf er from the radical anions of PFA and PFB to p-benzoquinone (Q), methy l viologen (MV(2+)), and 9,10-anthraquinone-2-sulfonate (AQS(-)). Stro ng reductants derived from reduction of 2,2-bipyridine (BpyH(.)) and 1 ,10-phenanthroline (PhenH(.)) can reduce both PFA and PFB. From the ki netics of these electron transfer reactions the reduction potentials o f PFA and PFB have been determined to be -0.86 +/- 0.1 and -0.75 +/- 0 .1 V vs NHE at pH 9.4. addition of OH. radical to the aromatic ring of these fluorinated compounds led to rapid HF elimination and the forma tion of phenoxyl radicals, and addition of H-. atoms led to the format ion of cyclohexadienyl radical.