Toluyl-o-Benzoic Acid

Methylanthraquinone. Use 10 5 g. of p-toluyl-o-benzoic acid (preceding Section) and 90 g. (46 ml.) of fuming sulphuric acid (20 per cent. SO3). RecrystaUise the product from alcohol in the presence of a little decolourising carbon. The yield of pure p-methylanthraquinone, m.p. 176°, is 7 - 5 g. 

Methyl anthraquinone has been obtained by the oxidation of /3-methyl anthracene by several investigators 1 and material of the same origin, obtained by the benzene-extraction of crude commercial anthraquinone,2 has been fully described. As regards the synthesis from phthalic anhydride and toluene, both the preparation and properties of />-toluyl-o-benzoic acid 3 and the complete synthesis 4 have been the subject of several papers. This acid has also been prepared from o-carbomethoxy benzoyl chloride and toluene.5 The phthalic anhydride synthesis of anthraquinone derivatives in general has received considerable attention. An account of this work, together with extensive references, is given by Barnett.6... 

The only practical method for the preparation of />-toluyl-o-benzoic acid is that proposed by Friedel and Crafts.1 Limpricht 2 has proposed a decrease in the quantity of aluminium chloride, but Heller and Schulke 3 and McMullen 4 have verified the importance of an excess of the condensing agent. 

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