Abstract
Polycyclic aromatic compounds (PACs) have historically occupied a cornerstone position in the development of the dye industry on account of their high degree of unsaturation and conjugation. We have for some years required our students to synthesize the vat dye violanthrone (also called dibenzanthrone), a nonacyclic diketone. This multistep synthesis involves as key steps: a) the reaction of anthraquinone (prepared in situ) with glycerol in acidic medium and copper sulfate to give 7H-benz[d,e]anthr-7-one (benzanthrone) b) the dimerization of benzanthrone with sodium chlorate to violanthrone The mechanism of step a) has proven particularly elusive to our students and worthwhile examining. Our extensive search of the literature simply revealed the reaction mechanism in bits and pieces. We describe herein a plausible mechanism, with the use of curved arrows to represent electron movement, for the syntheses of benzanthrone and violanthrone starting from 2-benzoylbenzoic acid, glycerol, copper sulfate, iron and sulfuric acid.
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