On the Mechanism of the Cathodic Reduction of Anthraquinone to Anthrone

The cathodic reduction of anthraquinone in 85% H 2 SO 4 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 AQH 2 and anthrahydroquinone AQH·. Both are subject to a bimolecular follow up reaction (disproportionation) to yield AQH 2 and anthrone. The rate constants are estimated to be 2 · 10 3 and 3 · 10 4 1 mol −1 s −1 , respectively. Anthrone is the only reduction product which could be isolated.