Dihydroxyanthraquinones

Materials. Beside inorganic materials (eg, barium chloride/fluoride crystals, doped with 0.05% samarium), transparent thermoplasts are preferred for the PHB technique, eg, poly (methyl methacrylate) (PMAIA), polycarbonate, and polybutyral doped with small amounts of suitable organic dyes, organic pigments like phthalocyanines, 9-arninoacridine, 1,4-dihydroxyanthraquinone [81-64-1] (quinizarin) (1), and 2,3-dihydroporphyrin (chlorin) (2). 

Dihydroxyanthraquinone. This anthraquinone, also known as quinizarin [81-64-1] (29), is of great importance in manufacturing disperse, acid, and vat dyes. It is manufactured by condensation of phthalic anhydride (27) with 4-chlorophenol [106-48-9] (28) in oleum in the presence of boric acid or boron trifluoride (40,41). Improved processes for reducing waste acid have been reported (42), and yield is around 80% on the basis of 4-chlorophenol. 

Diaminoanthraquinone and Related Compounds. Leuco-l,4-diaminoanthraquinone [81-63-0] (leucamine) (32) is an important precursor for 1,4 diaminoanthraquinone [128-95-0] (33) and is prepared by heating 1,4-dihydroxyanthraquinone (29) with sodium dithionite in aqueous ammonia under pressure. 

Anthracyclinones.1 Phthaloyl dichlorides undergo Friedel Crafts reactions with hydroquinones or the dimethyl ethers to give 1,4-dihydroxyanthraquinones in one step. 

In a related series of 1,2,4-trisubstituted anthraquinone compounds, the effectiveness of various polar and nonpolar substituents to improve on the low heat fastness of 2-amino-1,4-dihydroxyanthraquinone (3.184 R = H) was examined (Table 3.50). Short-chain alkyl groups (methyl, ethyl) and even the pyranylmethyl ether are relatively ineffective but hydroxyalkyl, cyclohexyl, benzyl and morpholinylethyl groups show moderate increases. Further improvement is given by phenyl, pyridylmethyl and morpholinylpropyl. Outstandingly effective, however, are the benzothiazolyl, dodecylphenyl and fluoro-methylphenyl groupings. 

Although anthraquinone is the starting point for the preparation of many derivatives, involving substitution and replacement reactions, certain compounds are obtained directly by varying the components in the above synthesis. Thus, for example, replacement of benzene with methylbenzene (toluene) leads to the formation of 2-methylanthraquinone. A particularly important variation on the phthalic anhydride route is the synthesis of 1,4-dihydroxyanthraquinone (6.6 quinizarin) using 4-chlorophenol with sulphuric acid and boric acid as catalyst (Scheme 6.3). The absence of aluminium chloride permits hydrolysis of the chloro substituent to take place. 

The first group includes 1,2-dihydroxyanthraquinone, commonly known as alizarin, 1,4-dihydroxyanthraquinone (quinizarin), and 1,2,4-trihydroxyan-thraquinone (purpurin). Alizarin in particular has been known and appreciated for thousands of years in the form of its lake , i.e., the coordination complex of 1,2-hydroxyanthraquinone 88 with aluminum and calcium (Madder Lake, Turkey Red). 

Quinizarin.—1 4-dihydroxyanthraquinone is of no use as a dye it has been found, as a general rule, that only those polyhydroxyquinones of the anthracene and naphthalene series (naphthazarin) which have their adjacent OH-groups in positions adjoining the carbonyl group are capable of forming colour lakes. 

In the source table the compound was named 1,8-Bis(prop-2 -enyloxy)anthraquinone, but it must be 1,4-Bis(prop-2 -enyloxy)anthraquinone as the authors synthesized it from 1,4-Dihydroxyanthraquinone. Figure 1 in the source also shows this 1,4- form. 

CAS 81-64-1 EINECS/ELINCS 201-368-7 Synonyms Cl 58050 1,4-Dihydroxyanthraquinone 1,4-Dihydroxy-9,10-anthraquinone... 

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