Hydroxyanthraquinones Carminic Acid and Chrysazin Anodic Oxidation

• Published in: Electroanalysis (New York, N.Y.) Vol. 24; no. 11; pp. 2079 - 2084
• Main Authors: De Souza Gil, Eric, De Oliveira, Severino Carlos B, De Oliveira-Brett, Ana Maria
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-11-2012; WILEY‐VCH Verlag
• Subjects: Anodizing; Anthraquinones; Carminic acid; Cascades; Catechol; Chromium; Chrysazin; Hydroquinone; Hydroxyanthraquinones; Oxidation; Oxidation mechanism; Tautomerism; Tautomers
• ISSN: 1040-0397; 1521-4109
• DOI: 10.1002/elan.201200433

The anodic oxidation of the hydroxyanthraquinones carminic acid (CA) and chrysazin (CR) was investigated. The oxidation of CA proceeds in a pH‐dependent cascade mechanism, concerning the hydroquinone, the catechol and the 3‐OH groups in the anthraquinone moiety. The oxidation of the hydroquinone following the catechol electron‐donating groups occurs first at low positive potentials, the 3‐OH group is oxidized irreversibly at a higher potential. The oxidation of CR is pH‐dependent and occurs in successive steps. Oxidation of the hydroquinone tautomer in the CR‐ring occurs first, and the symmetrical 1‐OH and 8‐OH groups are irreversibly oxidized at the same higher potential.