2-(4-Phenoxybenzoyl)benzoic acid → 2-Hydroxyanthraquinone

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2-phenoxyanthraquinonedisulfonic acid formed as an intermediate product in the course of preparing 2-phenoxyanthraquinonepolysulfonic acid from 2-phenoxyanthraquinone or 2-(p-phenoxybenzoyl) benzoic acid was confirmed, by way of a proton-NMR-absorption spectrum thereof, as having such a structure that the two sulfonic acid groups are bonded, as shown in the reaction formulas (1), to o- and p-positions of the phenoxy group in the 2-phenoxyanthraquinone. FIG. 3 shows a proton-NMR-absorption spectrum (solvent: dimethylacetamide; measuring temp.: room temperature) of sodium 2-phenoxyanthraquinonedisulfonate. This spectrum shows that in the compound of the formula (VII): ##STR11## absorption of proton f is detected in 8.44 ppm (1H), absorption of protons c, h in 8.04-8.3 ppm (3H), absorption of protons e, g in 7.83-8.02 ppm (3H), absorption of proton a in 7.61 ppm (1H), absorption of proton b in 7.42 ppm (1H) and absorption of proton d in 7.1 ppm (1H). It is confirmed therefore that 2-phenoxyanthraquinonedisulfonic acid has the structure shown by the formula (VII). The structure of the formula (VII) is supported also by the fact that when this 2-phenoxyanthraquinonedisulfonic acid is treated under heating with a 5% aqueous solution of sodium hydroxide, the phenoxy group of this compound is split off to afford 2-hydroxyanthraquinone.

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