PULSE-RADIOLYSIS STUDY OF ONE-ELECTRON REDUCTION REACTION OF FLUORANIL IN AQUEOUS-SOLUTION

Hydrated electron reacts with fluoranil (tetrafluoro-1,4-benzoquinone) with a rate constant of 2.5 x 10(10) M(-1) s(-1) to yield fluoranil a nion. The kinetics of the reaction was monitored at 300 and at 700 nm for the anion and e(aq)(-), respectively. The buildup of the anion abs orption was concomitant with the decay of hydrated electron as a conse quence of scavenging, suggesting that electron addition does not lead to concerted fluoride elimination. The anion disproportionates with a rate constant of 2k = 5.6 x 10(8) M(-1) s(-1), suggesting that fluorid e elimination from the anion is insignificant. It has low pK(a) = -1, reflecting a strong inductive effect of fluorine. The rate constants f or electron transfer to fluoranil from several reducing radicals have been determined. In the case of p-benzosemiquinone radical (QH(.)), an electron-transfer reaction with fluoranil (FL) leads to an equilibriu m; the rate constant of approach to the equilibrium yields the redox p otential of fluoranil E(Fl/Fl(.-)) = 180 mV vs NHE at pH 1.7.