Prepn from isoamyl alcohol: Fischer et al., Ber. 64, 30 (1931); Fischer, L"owenberg, Ann. 494, 272 (1932); cf. Burkhardt et al., GB 512465 (1939); Montavon, Saucy, US 2902515 (1959 to Hoffmann-La Roche). Absorption spectrum: Forbes, Skilton, J. Org. Chem. 24, 436 (1959).