Occurrence: in petroleum, Mabery, J. Am. Chem. Soc. 30, 143 (1908); in natural gas and in refinery cracking products. Prepd from C2H5I and sodium amalgam: L"owig, Jahresber. Fortschr. Chem. 1860, 397, Beilstein vol. 1, 118. Recovery of butanes from natural and refinery gases: Kirkbride, Bertelli, Ind. Eng. Chem. 35, 1242 (1943); Walters, ibid. 47, 2544 (1955); Gilmore, Bauer, Oil Gas J. 50, 84, 90, 94, 119 (1951), C.A. 46, 1743d (1952). Separation of butane and isobutane: Stone, Pet. Refin. 25(4), 164 (1946), C.A. 43, 2414 (1949). Handbook: Butane-Propane Gases, L. C. Denny et al., Eds. (Chilton Co., Los Angeles, 4th ed., 1962) 383 pp.