Phenol with Phthalic Anhydride to a derivative of Anthraquinone

Reaction XXIX. (b) Condensation of a Phenol with Phthalic Anhydride to a derivative of Anthraquinone. (A., 212, 10.)—When equimole-cular quantities of phthalic anhydride and a phenol react at 180° in the presence of cone, sulphuric acid, the product is not a phthalein, but the action takes a different course, and a derivative of anthraquinone is obtained. 

Alizarin (1 2-dihydroxyanthraquinone) and an isomer, hystazarin (2 3-dihydroxyanthraquinone), are also formed in this way from catechol and phthalic anhydride. 

40 gms. (excess) phthalic anhydride and 10 gms. (1 mol.) of pure quinol are heated for 3 hours in a flask in an oil bath at 170°—180° with 200 gms. pure cone, sulphuric acid and 20 c.cs. of water. It is then heated for 1 hour at 190°—200°. The hot solution is gently poured into about a litre of cold water in a large basin. The whole is then heated to boiling and filtered hot with suction. The residue is again extracted with boiling water and filtered hot. It is then boiled up with 400 c.cs. glacial acetic acid and filtered hot, to remove carbonaceous matter. The filtrate is 

—20% theoretical (4 gins.). Dark red needles from toluene, orange-yellow leaves from glacial acetic acid M.P. 195° insoluble in water. (B., 8, 152 A., 212, 10 0. S., VI., 78.) 

—The quinizarin which solidifies in the neck of the retort may be recovered by distilling some glacial acetic acid from the retort, a distilling flask being used as receiver. Acetic acid vapour is inflammable, and care should be taken that it does not become ignited. 

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