Hydroxyanthraquinones Carminic Acid and Chrysazin Anodic Oxidation |
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Authors: | Eric de Souza Gil Severino Carlos B de Oliveira Ana Maria de Oliveira‐Brett |
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Institution: | 1. Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, 3004‐535 Coimbra, Portugal;2. Faculdade de Farmácia, Universidade Federal de Goiás, Setor Universitário, 74605‐220, Goiania, Goiás, Brasil |
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Abstract: | 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. |
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Keywords: | Hydroxyanthraquinones Carminic acid Chrysazin Oxidation mechanism Tautomerism |
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