Anthraquinone

Anthraquinone (9,10-dioxoanthracene) is an aromatic organic compound. It is a derivative of anthracene. It has the appearance of yellow or light gray to gray-green solid crystalline powder.

Its other names are 9,10-anthracenedione, anthradione, 9,10-anthrachinon, anthracene-9,10-quinone, 9,10-dihydro-9,10-dioxoanthracene, and trade names Hoelite, Morkit, Corbit, and others.

Physical properties
It is insoluble in water but dissolves in alcohol, nitrobenzene and aniline. It is chemically fairly stable under normal conditions.

Natural occurrences
Anthraquinone naturally occurs in some plants (eg. aloe, senna, rhubarb, and Cascara buckthorn), fungi, lichens, and insects, where it serves as a basic skeleton for their pigments. Natural anthraquinone derivatives tend to have laxative effects.

Chemistry
There are several ways to obtain anthraquinone:
 * Oxidation of anthracene
 * Condensation of benzene with phthalic anhydride in presence of AlCl3 (Friedel-Crafts substitution). The resulting o-benzoylbenzoic acid then undergoes cyclization, forming anthraquinone.
 * Diels-Alder reaction (from naphthoquinone and a 1,3-diene followed by oxidation)
 * Retro-DA reaction: the Rickert-Alder reaction.

In a classic organic reaction called the Bally-Scholl synthesis (1905), anthraquinone condenses with glycerol forming benzanthrone. In this reaction the quinone is first reduced with copper metal in sulfuric acid (converting one ketone group into a methylene group) after which the glycerol is added.

Industrial applications
Anthraquinone is used in production of dyes, such as alizarin. Many natural pigments are derivatives of anthraquinone. Anthraquinone is also used as a catalyst in production of wood pulp in pulp and paper industry. Another use is as a bird repellant on seeds.

A derivative of anthraquinone (2-ethylanthraquinone) is used to produce hydrogen peroxide commercially.

Medical uses
Anthraquinone is used as a laxative. Prolonged use and abuse leads to melanosis coli.