anthraquinone

anthraquinone, the most important quinone derivative of anthracene and the parent substance of a large class of dyes and pigments. It is prepared commercially by oxidation of anthracene or condensation of benzene and phthalic anhydride, followed by dehydration of the condensation product.

Alizarin and many other vegetable pigments have chemical structures similar to anthraquinone. Anthraquinone can be converted to alizarin and to a number of synthetic dyestuffs, including a large family of vat dyes.

Although extremely stable toward oxidation, anthraquinone can be easily reduced to a variety of products. In alkaline solution, sodium dithionite reduces it to anthrahydroquinone, the alkali metal salts of which are water-soluble. The use of anthraquinones as vat dyes depends on this chemical reaction.