Pulse radiolysis of 4-tert-butyl-1,2-dihydroxybenzene and 4-tert-butyl-1,2-quinone

Abstract

A study has been made in aqueous solution of the radicals produced by hydroxyl radical attack on 4-tert-butyl-1,2-dihydroxybenzene, and by attack of solvated electrons and hydrogen atoms on 4-tert-butyl-1,2-quinone by the technique of pulse radiolysis using optical absorption for the detection of transients. Reaction rates with primary radicals were determined. The spectrum of the semiquinone radical, obtained in acid solution by reaction of OH with the hydroquinone, has absorption maxima at 290 and 390 nm, with extinction coefficients of about 7700 and 1850 M/sup -1/ cm/sup -1/, respectively. The spectrum of the semiquinone anion, obtained by reduction of the quinone in neutral solution, shows a maximum at 313 nm with a shoulder at 350 nm, having extinction coefficients of about 12200 and 2400 M/sup -1/ cm/sup -1/, respectively. The pK/sub a/ of the semiquinone radical is 5.2. The absorbance at 310 nm produced by the reaction of hydroxyl radicals with 4-tert-butyl-1,2-dihydroxybenzene decays by second-order kinetics below pH 7.5. At pH 3, 2k/sub bi/ = 9.0 X 10/sup 8/ M/sup -1/ s/sup -1/ was obtained for the bimolecular reaction of two semiquinone radicals. As the pH is increased, the rate of second-order decay decreases dramatically, the computed rate constant for bimolecularmore » reaction of two radical anion molecules being 2k/sub bi/ less than or equal to 4 X 10/sup 6/ M/sup -1/ s/sup -1/. The initial radical spectra andabsorbance decay kinetics found in alkaline solutions differ from that in acid and neutral solution, absorbance decay proceeding mainly by first-order kinetics.« less