Dihydroxyviolanthrone (I) [128-59-6] was prepd. by oxidn. of 4,4'-bibenzanthrone [116-90-5] to dioxoviolanthrone (II) [64346-54-9] with electrogenerated Mn+3+ and redn. of II to I with SO2. A decrease in current efficiency was obsd. after each cycle due to org. material carried over with electrolyte back to the electrochem. reactor. A simple relation was derived for the estn. of the loss in current efficiency due to the org. material present in the electrolyte. [on SciFinder (R)]