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.).