One-electron reactions of 1,5- and 1,8-dihydroxy-9, 10-anthraquinones. A pulse radiolysis study
- 1 January 1991
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions
- Vol. 87 (8) , 1109-1116
- https://doi.org/10.1039/ft9918701109
Abstract
Absorption characteristics of the semiquinone free radicals formed by the one-electron reduction (using e– aq, CO˙– 2 and CH3ĊOHCH3 as the reductant) as well as the oxidation (using OH˙, O˙– and N˙ 3 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 pKa= 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 E1 11=–350 mV (for 1,5-DHAQ) and E1 11=–377 mV (for 1,8-DHAQ), respectively. Differences with 1,4-dihydroxy-9, 10-anthraquinone (quinizarin) are discussed.Keywords
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