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Alizarin

acid, anthraquinone and sulphuric

ALIZARIN (from alizari, the commercial name of madder in the East), a substance hav ing the formula CulieDa.(OH).„ formerly ob tained from the root of the madder (Rubio tinctoria), but now artificially produced from coal-tar and the refuse from the distillation of crude petroleum. It is used as a dye, for pro ducing the color known as °turkey red.' Aliza rin is of interest to the chemist not only on account of its industrial importance, but also because it was the first vegetable coloring mat ter to be produced artificially; and the year 1868, in which its synthesis was effected by W. H. Perkin, therefore marks the beginning of a new era in industrial chemistry. In the manufac ture of alizarin, anthracene (Cul-110) is first pre pared from coal-tar, and by oxidation (which it readily undergoes under the influence of potassium bichromate or other oxidizing agent) is transformed into anthraquinone, C.41-1.03. The next step is to sulphonate the substance so formed. Anthraquinone is remarkably stable toward sulphuric acid, but combination can be effected by strongly heating a mixture of the two, and a solution of mono- and disulphonic acids of anthraquinone is the result. The excess

of sulphuric acid is then removed, and the sul phonic acids are heated with caustic potash to about 350° F. The mass gradually darkens till it becomes almost black, at which stage it dis solves in water with the formation of a rich purple solution, from which alizarin can be pre cipitated in abundance by the addition of sul phuric acid. A similar process was also devised by Perkin, in which the first step is the forma tion of dichloranthracene, by treating anthracene with chlorine. Subsequent treat ment of this body with sulphuric acid gives anthraquinone disulphonic acid, C.1-1.0, (HSO.).. This is fused with potash, as de scribed above, and the alizarin precipitated with sulphuric acid as before. Anthrapurpurin is formed, simultaneously with alizarin, in the processes given above. Its behavior as a dye is similar to that of alizarin, but it gives a brighter red. Pure alizarin, as obtained by sublimation. crystallizes in yellowish-red crystals, only slightly soluble in alcohol or water, but readily dissolving in alkalis. Chemically, alizarin is known as dioxyanthraquinone.