Anthraquinone: Phthalic Anhydride and Benzene over Aluminium Chloride, Heller

Anthraquinone is the yellow crystalline starting material for alizarin and other dyes. Instead of oxidising coal-tar anthracene, Heller's route (1906, in Thorpe's Dictionary 1912) builds it from phthalic anhydride and benzene with aluminium chloride: the two join to benzoylbenzoic acid, which closes to anthraquinone on heating at 150 °C. Benzene is poisonous and hydrogen chloride comes off: work in a fume hood. The picture: our diagram.