One-electron Reactions of 1,5- and 1,8-Dihydroxy-9,10-anthraquinones. A Pulse Radiolysis Study

Article abstract of DOI:10.1039/ft9918701109

Absorption characteristics of the semiquinone free radicals formed by one-electron reduction (using e^-_aq, CO2^.- and CH3C^.COHCH3 as the reductant) as well as the oxidation (using OH^., O^.- and N3^. as the oxidants) of 1,5-dihydroxy-9,10-anthraquinone (1,5-DHAQ) and 1,8-dihydroxy-9,10-anthraquinone (1,8-DHAQ) have been studied by pulse radiolysis in pure isopropyl alcohol and in aqueous solutions containing various appropriate additives.The first acid dissociation constants for the reduced semiquinones were measured as pK_a = 3.65 and 3.95 for 1,5-DHAQ and 1,8-DHAQ, respectively.Second-order rate constants for various formation and decay reactions have been determined.The one-electron reduction potentials (vs.NHE) were determined at pH 11, as E¹₁₁ = -350 mV (for 1,5-DHAQ) and E¹₁₁ = -377 mV (for 1,8-DHAQ), respectively.Differences with 1,4-dihydroxy-9,10-anthraquinone (quinizarin) are discussed.