Found in coal tar and in bone oil. Synthesis (40-50% yield) from cyclohexylamine with excess ammonia and zinc chloride at 350°: Nordt, PB Report 704 (1941). Prepn from ethylene-mercuric acetate adduct and ammonia water (70% yield): Gumboldt, Feichtinger, Z. Naturforsch. 4b, 123 (1949). Toxicity study: H. F. Smyth et al., Arch. Ind. Hyg. Occup. Med. 4, 119 (1951). Physical properties: Biddiscombe et al., J. Chem. Soc. 1954, 1957. Review of the various methods of condensing aldehydes, ketones, ethylene, butadiene, etc., with ammonia: F. Brody, P. R. Ruby in A. Weissberger, The Chemistry of Heterocyclic Compounds vol. 14, part I (New York, 1960) pp 99-589. Contains 1851 references.