On the Mechanism of the Cathodic Reduction of Anthraquinone to Anthrone

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Abstract
The cathodic reduction of anthraquinone in 85% H2SO4 at cathodes of glassy carbon or mercury has been investigated. Voltammetric curves exhibit two steps at +0.23 and +0.10 V vs. SHE. The limiting current densities show a ratio between 4:0 via 1:1 to 1:3, depending on the experimental conditions. Experiments at the RRDE indicate two reoxidizable intermediates.—We derive a mechanism from our Findings, involving the electrochemical formation of these intermediates, anthrasemiquinone AQH2 and anthrahydroquinone AQH·. Both are subject to a bimolecular follow up reaction (disproportionation) to yield AQH2 and anthrone. The rate constants are estimated to be 2 · 103 and 3 · 104 1 mol−1 s−1, respectively. Anthrone is the only reduction product which could be isolated.