The electrochemical reduction mechanism of anthraquinone (AQ) has been
studied in N,N-dimethyl formamide (DMF) and/or its water mixtures by
means direct current polarography (DCP) and differential pulse polarog
raphy (DPP). The polarograms consisted of two well-defined waves in an
hydrous DMF. The presence of small amounts of water does not effect th
e first wave but causes the second wave to shift toward more positive
potentials; large amounts of water (solutions with at least 40% water)
give a single wave. Half-wave potentials for the one-electron step in
DMF are more negative than those in aqueous solutions and have been u
sed to calculate the disproportionation constant, K(D), of the radical
anion in each solution. The reduction potentials in aqueous solutions
have been analyzed on the basis of the Heyrovsky model. Results show
that the electrode process is a two electron-two proton conversion of
the AQ quinone to dihydroxyanthracene (in acidic media) or its dianion
(in alkali media). From these results a reduction mechanism has been
proposed for AQ in both aprotic and protic solvents.