Made by the oxidation of acenaphthene with chromic acid mixture, etc.: Graebe, Gfeller, Ber. 25, 652 (1895); Ogilvie, Wilder, US 2379032 (1945 to Allied Chem.); Karishin, Fedorenko, Zh. Prikl. Khim. 29, 955 (1956), C.A. 50, 14677b (1956).