This sesquiterpene, which was first discovered by Piccard, and which up to the present time has been found only in oil of hops and oil of poplar buds, closely resembles caryophyllene. Thus far the attempts to regenerate humulene from one of its derivatives have not been successful. Hence the constants had to be ascertained in connection with more or less pure fractions. Chapman,1) who has devoted much study to the characterization of this sesquiterpene, records the following:
B. p. 263 to 266° (760 mm.); d15o 0,9001; aD - 0,5°; nD 1,5021.
The hydrocarbon obtained from poplar bud oil was slightly dextrogyrate. It is probable, however, that humulene itself is optically inactive and that the slight rotation was due to impurities.
1) Journ. chem. Soc. 67 (1895), 54.
Hydrogen chloride, when added, yields a liquid dihydrochloride, bromine an oily tetrabromide. Upon hydration an alcohol results. Mitrosyl chloride is added with the formation of a nitrosochloride melting at 164 to 165°, respectively at 164 to 170°. The nitrolbenzyl-amine base melts at 136°, respectively at 132 to 133°; the nitrol-piperidine base at 153°. Nitrous acid is added with the formation of a nitrosite melting at 120 to 121°, and of an isonitrosite melting at 166 to 168°. Both of these, when treated with sodium ethylate, yield nitroso- or /'sonitrosohumulene, b. p. 185 to 195° (13 mm). The nitrosate, m. p. 162 to 163°, is also known. Humulene can be identified by means of its nitrosochloride in the usual manner.