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Hydroxyanthraquinones Carminic Acid and Chrysazin Anodic Oxidation

Authors

  • Eric de Souza Gil,

    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, Goiânia, Goiás, Brasil
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  • Severino Carlos B. de Oliveira,

    1. Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra, Portugal
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  • Ana Maria de Oliveira-Brett

    Corresponding author
    1. Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra, Portugal
    • Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra, Portugal
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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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