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Org. Synth. 1925, 4, 43
DOI: 10.15227/orgsyn.004.0043
β-METHYLANTHRAQUINONE
[Anthraquinone, 2-methyl-]
Submitted by L. F. Fieser
Checked by Roger Adams and R. L. Shriner.
1. Procedure
The p-toluyl-o-benzoic acid which is obtained from 100 g. of phthalic anhydride (p. 517), and which should weigh 157 g. (0.65 mole), is mixed with 1400 g. (725 cc.) of fuming sulfuric acid (20 per cent anhydride) (Note 1) in a 2-l. flask protected by a calcium chloride tube, and the mixture is heated on the steam bath for two hours with occasional shaking (Note 2). The clear, deep red solution is poured when cold upon cracked ice in a 4-l. beaker. The methyl anthraquinone separates and is digested for twenty minutes by passing in steam, after which it is filtered by suction. A flannel cloth is used in the filter, or a filtros plate may be cemented into a Büchner funnel with water-glass. The precipitate is washed well with hot water, after which it is returned to the beaker and digested as before with hot water to which is added a slight excess of ammonia, beyond that required to neutralize any acid present.
The product is filtered and dried to constant weight. The filtrate will be clear and will give no precipitate with hydrochloric acid if the conditions of condensation have been correct.
The β-methylanthraquinone is pale tan in color and weighs from 118 to 130 g. (81–90 per cent of the theoretical amount, based upon the weight of acid taken). It is practically pure, melting at 173°. Upon crystallization from alcohol in the presence of animal charcoal, it forms long, silken, almost colorless needles, melting constantly at 173.5° (176° corr.).
2. Notes
1. Some investigators have used concentrated instead of fuming sulfuric acid for the condensation, but the yield is usually low and the product is always colored bright yellow by some impurity which cannot be removed by crystallization.
2. The time allowed for condensation may be shortened to one-half, without affecting the yield, by maintaining the temperature at 125–130°.
3. Discussion
β-Methylanthraquinone can be prepared by the oxidation of β-methylanthracene1 and material of the same origin, obtained by the benzene-extraction of crude commercial anthraquinone;2 from the intramolecular condensation of p-toluyl-o-benzoic acid;3 and from o-carbomethoxybenzoyl chloride and toluene.4
This preparation is referenced from:

References and Notes
  1. Fischer, Ber. 8, 675 (1875); J. prakt. Chem. (2) 79, 560 (1909); Fischer and Gross, J. prakt. Chem. (2) 82, 232 (1910); Fischer, Falco, and Gross, ibid. (2) 83, 210 (1911); Lavaux, Ann. chim. phys. (8) 20, 445 (1910); I. G. Farbenind. A.-G., Brit. pat. 253,911 and Swiss pat. 124,266 [Chem. Zentr. II, 1820 (1928)].
  2. Perkin and Cope, J. Chem. Soc. 65, 843 (1894); Wachendorff and Zincke, Ber. 10, 1485 (1877); Börnstein, Ber. 15, 1820 (1882); Römer and Link, Ber. 16, 696 (1883).
  3. Elbs, J. prakt. Chem. (2) 33, 319 (1886); (2) 41, 4 (1890); Gresby, Ann. 234, 239 (1886); Limpricht, Ann. 299, 300 (1898); Ber. 28, 1134 (1895); Limpricht and Weigand, Ann. 311, 180 (1900); Heller and Schülke, Ber. 41, 3632 (1908); Krassovski, J. Russ. Phys. Chem. Soc. 46, 1067 (1914) [Chem. Zentr. I 999 (1915)].
  4. Smith, J. Am. Chem. Soc. 43, 1922 (1921).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

p-Toluyl-o-benzoic acid

sulfuric acid (7664-93-9)

hydrochloric acid (7647-01-0)

ammonia (7664-41-7)

phthalic anhydride (85-44-9)

Anthraquinone (84-65-1)

toluene (108-88-3)

β-Methylanthraquinone,
Anthraquinone, 2-methyl- (84-54-8)

methyl anthraquinone

β-methylanthracene (613-12-7)

o-carbomethoxybenzoyl chloride