Prepd from methylene chloride and benzene with aluminum chloride as catalyst: Friedel, Crafts, Bull. Soc. Chim. [2] 41, 324 (1884); from benzyl chloride and benzene: Hartman, Phillips, Org. Synth. 14, 34 (1934); L. F. Fieser, Experiments in Organic Chemistry (Boston, 3rd ed., 1955) p 157. Absorption spectrum in hexane: Castille, Bull. Soc. Chim. Belg. 36, 296; Chem. Zentralbl. 1927, I, 1126; in alcohol: Ondorff, J. Am. Chem. Soc. 49, 1541 (1927)