PULSE RADIOLYTIC ONE-ELECTRON REDUCTION OF 2-HYDROXY-9,10-ANTHRAQUINONES AND 2,6-DIHYDROXY-9,10-ANTHRAQUINONES

The semiquinone free radicals produced by one-electron reduction of 2- hydroxy-9,10-anthraquinone (2HAQ) and 2,6-dihydroxy-9,10-anthraquinone (26DHAQ) in aqueous formate solution, water-isopropyl alcohol-acetone mixed solvent and isopropyl alcohol have been studied using the pulse radiolysis technique. The absorption characteristics, kinetic paramet ers of formation and decay, acid-base behaviour and redox characterist ics of the semiquinones have been investigated and compared with the c orresponding characteristics of a few intramolecularly hydrogen-bonded anthrasemiquinone derivatives. The non-hydrogen-bonded semiquinones s how two pK(a) values (4.7 and 10.7 for 2HAQ and 5.4 and 8.7 for 26DHAQ , respectively) within the pH range 1-14, whereas other intramolecular ly hydrogen-bonded semiquinones show only one pK(a). The one-electron reduction potential (E7') values for 2HAQ (-440 mV) and 26DHAQ (-400 m V) are more negative than those of the intramolecularly hydrogen-bonde d systems.