Electrochemical process for benzanthrones and planar polycyclic aromatic oxo compounds

The title compds., useful in the prodn. of dye intermediates, are prepd. in acid media in an electrolysis cell whose electrodes are sepd. by a membrane. At the cathode, anthraquinones are reductively cyclized with glycerol [56-81-5] to give the corresponding benzanthrones. In the anode chamber the oxidn. state of a transition metal ion is electrochem. increased by 1 and the resulting ion serves as a chem. oxidant for a planar polycyclic arom. compd. Thus, to the cathode chamber contg. 46.8 g anthraquinone [84-65-1] in 1300 g H2SO4, 31.05 g glycerol was added dropwise while the current was running. On the anodic side 10 g MnSO4.H2O was suspended in 130 g 88% H2SO4. benzanthrone [82-05-3] (85%) Was isolated from the cathodic portion, while the anolyte was used to cyclooxidize 10 g 4,4'-bibenzanthrone [116-90-5] to dioxoviolanthrone [64346-54-9] which was reduced with NaHSO3 to dihydroxyviolanthrone (I) [26545-62-0] in 76.4% yield. I was used as an intermediate in the synthesis of vat dyes. [on SciFinder (R)]