Nonaqueous Electrochemistry of 1-Hydroxy-9,10-Anthraquinone and Its Conjugate Base

Abstract

The electrochemical behaviors of l‐hydroxy‐9,10‐anthraquinone (HOAQ) and its conjugate base false(OAQ−false) have been compared in DMF and acetonitrile solvents, HOAQ is reduced in two one‐electron steps to stable anion radical and dianion, while OAQ− reduces in a single two‐electron wave accompanied by a monoprotonation reaction. Addition of phenol as proton source to DMF solutions of OAQ− forms a heteroconjugate acid‐base dimer, ØOH…OAQ− . This complex is reduced at a potential intermediate between that of HOAQ and OAQ− , and interpretation of its reaction includes consideration of concomitant formation of ØOH…OØ− homoconjugate dimer. The conjugate base OAQ− is oxidizable by a one‐electron reaction which is followed by rapid hydrogen atom abstraction to yield HOAQ as product. Combined thin‐ layer spectroelectrochemical and coulometric measurements form an important supplement to the conventional electroanalytical methods used in this study.

The role of intramolecular hydrogen bonding in the electrochemical behavior of hydroxy-quinones and in semiquinone stability

“…4 -hydroxyquinones can present hydrogen bonding via the -carbon to the carbonyl function leading to a six-membered ring structure ( Figure 1); the hydroxyl group involved in these structures is usually part of a phenolic function. 5,6 When electron transfer reactions occur, the acidity level of both hydroxy functionalities must be taken in account in front of the stability of the formed semiquinone / dianion intermediaries. These last species are related to the reactivity that hydroxyquinone compounds, as it has been reported in many biological essays, particularly in oxygenquinone interaction studies.…”

Electrochemical and ESR study on the transformation processes of α-hydroxy-quinones

“…The presence of this type of hydroxy functionality seems to be related to the biological activity of this kind of compound [2][3][4][5][6][7], and the position of this functional group can alter the typical redox behavior of the quinoid moiety [8][9][10][11][12]. This is relevant, considering that most of the biological activity of quinonoid systems is related to their capacity to carry out free radical generation via redox reactions.…”

pH- and temperature-responsive redox behavior of hydroxyanthracenediones

“…The quinones and anthracenediones undergo two successive one-electron reduction steps to produce the corresponding semiquinone and dianion, generating two separate cathodic waves in which the first step is fully electrochemically reversible and the second step is either reversible or quasi-reversible, depending on the experimental conditions [17][18][19][20][21]. Anthracenediones containing hydroxyl groups are interesting from an electrochemical point of view, and their position alters the redox behavior of the quinonoid moiety [18,[22][23][24] due to the formation of intramolecular hydrogen bonds. In addition, these moieties are related to the biological activity of ACDs [25,26].…”

“…Though anthracenediones have a broad spectrum of applications and their reduction is widely studied [17][18][19][20][21][22][23][24], the literature about their electro-oxidation is limited and thus deserves further investigations. In the present work, we focus on the pH-dependent and temperature-dependent electro-oxidation of 4,8-dihydroxy-9,10-dioxo-9,10-dihydroanthracen-1-yl acetate (HACAD), 1,4,5-trihydroxyanthracene-9,10-dione (HAD) and 1,4,5-trihydroxy-2-methyl-3-(3-oxobutyl)anthracene-9,10-dione (HOAD), with the hope of providing useful insights into their electron transfer reactions.…”