STUDY OF THE REDOX BEHAVIOR OF ANTHRAQUINONE IN AQUEOUS-MEDIUM

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 polarography (DPP). The polarograms consisted of two well-defined waves in anhydrous DMF. The presence of small amounts of water does not effect the 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 used 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.