Occurs in teakwood. Prepd by oxidation of 2-methylanthracene; by formation from phthalic anhydride and toluene: Fieser, Org. Synth. 4, 43 (1925); from 6- and 7-methylanthraquinone-1-carboxylic acids with powdered copper in quinoline: Fieser, Martin, J. Am. Chem. Soc. 58, 1443 (1936); from 1,4-naphthoquinone and isoprene: Carothers, Berchet, ibid. 55, 2813 (1933).