C14H802

ANTHRAQUINONE  , 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 cylinders with a mixture of sodium bichromate and caustic 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 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 phthalic anhydride with benzene in the presence of aluminium chloride . This compound on heating with phosphoric anhydride loses water and yields anthraquinone, C6H4<CO>O ,CiH4`000Hj5~C6H4.<CO/ CsH4 . 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: CO•CHOH : C6H4, with tin and hydrochloric acid, the phenolic compound anthranol, C6H4: CO•C(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 .