Mechanistic Study of Electrochemical Oxidation of 2,5-Dihydroxybenzoic Acid and 3,4-Dihydroxybenzaldehyde in the Presence of 3-Hydroxy-1H-phenalene-1-one

Abstract

Quinones are of considerable interest because many drugs such as doxorubicin, daunurobicin and mitomycin C in cancer chemotherapy contain quinones, 1) whereas various other quinones have found use in industry.2) Some of them also exhibit antitumor and antimalarial activities 3) and many of them are also involved in enzyme inhibition and DNA cross-linking.4) On the other hand, in recent years, medicinal properties of benzofuran derivatives have been investigated widely and were shown to be effective as antitumor, 5) anti-depressant, 6) antifungal, 7) anti-hypertensive, and cytotoxic. 8) They are also potent and selective oxytocin antagonists, 9) PDE5 inhibitor for treatment of erectile dysfunction, 10) and H 3 receptor antagonists.11) In order to synthesise new quinone derivatives we studied the electrochemical oxidation of benzenediols in the presence of a variety of nucleophiles.12,13) Also, in order to synthesise benzofuran derivatives we investigated the electrochemical oxidation of catechols in the presence of b-diketones such as acetylacetone, 14) dimedone, 15) and dibenzoylmethane. 16) In this connection, the electrochemical oxidation of hydroquinones and catechols in the presence of 3-hydroxy-1H-phenalene-1-one (3) as a nucleophile has been recently reported by us (Chart 1). 17)In the present paper, we describe the preparation of the new polycyclic quinone derivative 6a and the new polycyclic benzofuran derivative 8b using electrooxidation of 2,5-dihydroxybenzoic acid (1a) and 3,4-dihydroxybenzaldehyde (1b) in the presence of 3-hydroxy-1H-phenalene-1-one (3) as a nucleophile via ECE and ECEC electrochemical mechanisms respectively. Results and DiscussionElectrochemical Study of 2,5 Dihydroxybenzoic Acid Cyclic voltammogram of a 0.5 mM of 2,5-dihydroxybenzoic acid (1a) in water/acetonitrile (80/20) solution containing 0.1 M acetate buffer (pHϭ5.5) is shown in Fig. 1 curve a. As can be seen, one anodic (A 1 ) and its corresponding cathodic peak (C 1 ) was obtained, which correspond to the transformation of 2,5-dihydroxybenzoic acid (1a) to the related p-benzoquinone 2a and vice versa within a quasi-reversible twoelectron process. A peak current ratio (I pA1 /I pC1 ) of nearly unity in the cyclic voltammogram can be considered as a criterion for a stable benzoquinone produced at the surface of electrode under the experimental conditions. In other words, any side reactions such as hydroxylation and/or dimerization reactions are too slow to be observed at the time scale of cyclic voltammetry.17) The oxidation of 2,5-dihydroxybenzoic acid (1a) in the presence of 3 as a nucleophile was studied in some detail. Figure 1 (curve b) shows the cyclic voltammogram obtained for a 0.5 mM solution of 1a in the presence of 0.5 mM 3. The voltammogram exhibits one anodic peak A 1 and two cathodic peaks (C 1 and C 0 ). The second cycle in the cyclic voltammogram (Fig. 1, curve c) shows that, parallel to the decrease in current of A 1 and the shift of its potential in a positive direction, a new anodic peak The mechanism of th...

Kinetics study of electrochemically induced michael reaction of benzoquinones with triphenylphosphine

“…These observations make it possible for us to propose the pathway in Scheme 2 for the electrooxidation of 3,4-dihydroxybenzoic acid (2) in the presence of triphenylphosphine (4). Furthermore, for high scan rates as well as acidic solutions [19,20], only peak C 1 is observed and the other cathodic peak (C 0 ) disappears. Under these conditions, the voltammogram shows a quasi-reversible two-electron process corresponding to a 2,5-dihydroxybenzoic acid (3)/3,6-dioxocyclohexa-1,4-dienecarboxylic acid (3a) redox couple [19][20][21].…”

Clean and Green Synthesis of New Benzothiazole Derivatives via Electrochemical Oxidation of Catechol Derivatives

“…Chem. Acta 2016, 89(1), [7][8][9][10][11][12][13][14][15] in the absence of 1a are shown in Figure 1, curves d and e. These compounds are electrochemically inactive in the range of the potential studied. In addition the cyclic voltammogram of isolated and purified product 6a was recorded under the same conditions but in DMF media (not soluble in water/DMF mixture).…”

“…Chem. Acta 2016, 89(1), [7][8][9][10][11][12][13][14][15] same electrodes as undivided cell with a fine glass frit sep arator. The anolyte was the reaction mixture with composition same as that was used in previous experiment (undivided cell).…”

“…[2,3] O-and p-quinines produced by oxidation of o-and p-catechols are unstable compounds, and can be used as an acceptor in the Micheleaddition reaction, which undergo attacks by nucleophiles such as 5-methyl-2-mercapto-1,3,4-thiadiazole, [4] 1,3-diethyl-2-thiobarbituric acid, [5] Meldrum's acid, [6] cyanoacetone, [7] and 3-hydroxy-1H-phenalene-1-one. [8] Thiouracils are minor components of transfer-RNA, have anti-herpes virus activities, and have been used for the treatment of hyperthyroidism in men. [9−13] With respect to the properties of these compounds, synthesis of derivatives of thiouracils by means of green chemistry becomes important.…”

Kinetics and Mechanistic Study of Acetaminophen‐Captopril Interaction by Electrochemical Methods

“…The obtained cyclic voltammograms during coulometry progress (Figure 4) shows that the final product does not participate in redox reaction. The sum total voltammetry and coulometry results imply on an ECEC electrochemical mechanism [15][16][17]. The proposed ECEC electrochemical mechanism is presented in Scheme 2.…”