Synthetic production of anthraquinone derivatives

Where selective introduction of substituents into the anthraquinone molecule is difficult, synthesis from smaller components is frequently used. The most important reaction component in this context is phthalic anhydride, which undergoes Friedel-Crafts reaction with other substituted aromatics such as chlorobenzene, chlorophenol or toluene to yield the desired anthraquinone derivative. 

Production of 1,4-dihydroxyanthraquinone (quinizarin) is a particularly important example. It is obtained by the reaction of phthalic anhydride with p-chloro-phenol at 170 to 190 °C. 

The boric acid ester, formed as an intermediate with quinizarin, prevents further oxidation, and is hydrolysed with steam at the boiling point. Crude quinizarin is subsequently refined by sublimation. 

Quinizarin is used as a raw material in the production of 1,4-diaminoanthraqui-none dyestuffs, such as e.g. Alizarine Cyanine Green G (Acid Green 25), which is obtained from quinizarin and p-toluidine, with subsequent sulfonation and neutralization. 

1 Reactors 2 Hydrolysis column 3 Washing vessel 4 Extractor 5 Precipitation vessel 6 Reactor 7 Dilution vessel 

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