ANTHRAQUINONE, C14H802

This article appears in Volume V02, Page 106 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: ANC-APO

ANTHRAQUINONE, C14H802 , an important derivative of anthracene, first prepared in x834 by A. Laurent. It is prepared commercially from anthracene by stirring a sludge of anthracene and water in

horizontal

HORIZONTAL

cylinders with a mixture of sodium bichromate and

caustic

CAUSTIC (Gr. rcavvraubs, burning)

soda. This suspension is then run through a conical mill in order to remove all grit, the cones of the mill fitting so tightly that water cannot pass through unless the mill is running; the

speed

SPEED, JOHN (1552–1629)

of the mill when working is about 3000 revolutions per minute. After this treatment, the mixture is run into lead-lined vats and treated with sulphuric acid, steam is blown through the mixture in order to bring it to the boil, and the anthracene is rapidly oxidized to anthraquinone. When the oxidation is complete. the anthraquinone is separated in a filterpress, washed and heated to r 20 C. with commercial oil of vitriol, using about 22 parts of vitriol to r of anthraquinone. It is then removed to lead-lined tanks and again washed with water and dried; the product obtained contains about 95 % of anthraquinone. It may be purified by sublimation. Various synthetic processes have been used for the preparation of anthraquinone. A. Behr and W. A. v. Dorp (Ber.,1874,7,p.578) obtained orthobenzoyl benzoic acid by

heating

HEATING

phthalic

PHTHALIC

anhydride with benzene in the presence of

aluminium

ALUMINIUM (symbol Al; atomic weight 27.0)

chloride. This compound on

heating

HEATING

with phosphoric anhydride loses water and yields anthraquinone,
C6H4O ,CiH4`000Hj5~C6H4.It may be prepared in a similar manner by heating phthalyl chloride with benzene in the presence of aluminium chloride. Dioxy- and tetraoxy-anthraquinones are obtained when meta-oxyand dimeta-dioxy-benzoic acids are heated with concentrated sulphuric acid.
Anthraquinone crystallizes in yellow needles or prisms, which melt at 277 C. It is soluble in hot benzene, sublimes easily, and is very stable towards oxidizing agents. On the other hand, it is readily attacked by reducing agents. With zinc dust in presence of caustic soda it yields the secondary alcohol oxanthranol, C6H4: COCHOH : C6H4, with tin and hydrochloric acid, the phenolic compound anthranol, C6H4: COC(OH): CsH4; and with hydriodic acid at r 5o C. or on distillation with zinc dust, the hydrocarbon anthracene, C44H10. When fused with caustic potash, it gives benzoic acid. It behaves more as a ketone than as a quinone, since with hydroxylamine it yields an oxime, and on reduction with zinc dust and caustic soda it yields a secondary alcohol, whilst it cannot be reduced by means of sulphurous acid. Various sulphonic acids of anthraquinone are known, as well as oxy-derivatives, for the preparation and properties of
which see ALIZARIN.

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