Abstract:
Electron-pulse and gamma radiolysis of “aqueous” solutions of the title compound (D) in the range pH 14 to > 100 % H2SO4 give the same products as photolysis (mainly α- and β-monohydroxyderivatives ROH with some polyhydroxylated D, and in the absence of oxygen, semiquinone and quinol), and the same variation with pH or acidity of the α : β ROH isomer ratio. Of the following rate constants (all in dm3 mol–1 s–1) the first three were determined by pulse radiolysis, the others by scavenger competition during gamma radiolysis : 2 DOH˙→ DHOH + ROH, 2 k=(1.41 ± 0.17)× 109; DOH˙+ O2→ DOH˙ O2., k=(1.39 ± 0.17)× 107; 2 D–˙→ D + D2–, 2 k=(1.33 ± 0.18)× 109; D + OH·→ DOH·, k=(2.68 ± 0.25)× 109; D + O·–→ DO·–, k= 6.1 × 107; D + O.–→ products other than DO.–, k= 1.63 × 108[this reaction is postulated to explain the fall in G(ROH) at pH > 12]. The effect of individual scavengers and of high alkalinity on the yield of ROH is different in photolysis and radiolysis. This suggests that since OH· is known to be the precursor of DOH· in radiolysis, any photolysis mechanism involving intermediate free OH· production is invalid.
