2-(2',5'-Dimethoxybenzoyl)-6-methoxybenzoic acid → 1,4,5-Trimethoxyanthraquinone

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Reaction Steps

2-(2',5'-Dimethoxybenzoyl)-6-methoxybenzoic acid (I) (3 g, 0.01 mole) was added in portions to stirred concentrated sulfuric acid (20 ml). After addition the mixture was heated on steam bath with constant stirring for 20 minutes, cooled to room temperature and poured onto crushed ice (400 g) and extracted with chloroform (3 × 100 ml). The organic extract was washed with 2% aqueous sodium hydroxide solution (10 × 100 ml) and water (100 ml), then dried over anhydrous sodium sulfate and the solvent stripped off under reduced pressure to yield 1,4,5-trimethoxyanthraquinone (II), as a brownish yellow solid (2.7 g, 90% yield). Recrystallization from ethanol gave yellow crystals, m.p. 201°-203° C.; IR (CDCl3), 5.92μ; NMR (CDCl3) δ, 7.88-7.20 (m, 5H), 3.94 (s, 3H), 3.92 (d, 6H). Calcd: C, 68.46; H, 4-70. Found: C, 68.33; H, 4.82.

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