Alizarine saphirol

Both of the dihydroxyanthraquinones are important starting materials for alizarin and indanthrene dyes. In mai cases, the two isomeric dihydroxyanthraquinones give very similar dyes, and a mixture of the two can be used directly (e.g., see alizarin saphirol B and SE). 

The main body of the solution of the nitro compound is then neutralized with soda ash to the point giving a permanent red coloration, and heated to 60-65°C. The calculated amount of concentrated hydrosulfide solution is added slowly with stirring, and the mixture is held at 60-65° for 3 hours. Enough salt is then added to make the solution 10 per cent with respect to salt, and the solution is cooled with stirring. The precipitated dye is filtered off, washed with 15 per cent salt solution until the washings are colorless, pressed out, and dried at 90°. The yield of alizarin saphirol B is about 105 grams. 

Technical Observations-. The dyes, prepared from 1,5- and 1,8-dihydroxy-anthraquinone by tHe above procedure, are so similar that frequently a mixture of the two is used. The SE dye can be prepared without isolating the intermediate disulfo dye (alizarin saphirol B), the reduced solution from the hydrosulfide reduction being treated directly with sodium sulfide. 

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