Prepn: L. Knorr, Ann. 301, 1 (1898); F. Chapman, J. Chem. Soc. 1949, 1631; G. Oláh et al., Ber. 89, 2374 (1956). Metabolism: B. W. Stewart, P. N. Magee, Biochem. J. 126, 21P (1972). Carcinogenicity studies: H. Druckrey et al., Naturwissenschaften 48, 134 (1961); P. Bannasch, H.-A. Müller, Arzneim.-Forsch. 14, 805 (1964); IARC Monographs 17, 263 (1978).