Indanthrene scarlet 4G with Raneynickel, aqueous sodium hydroxide and hydrogen. Reduction of (II) with aluminium tricyclohexoxide gave 3:4:9:10-dibenzopyrene (I), a potent carcinogen, which was isolated by Bonnet and Neukomm from tobacco smoke. Oxidation of 3:4:9:10-dibenzopyrene-5:8-quinone with chromic acid in glacial acetic acid gave pentaphene-5:14:8:13-diquinone (V). Reduction of (V) with aluminium