Oleum Humuli Lupuli. Hopfenol. - Essence de Houblon.
Origin and Production. Oil of hops is obtained by distillation of hops, i. e. the female inflorescences, also from the lupulin, the glands of Humulus Lupulus, L. (family Moraceae). From hops the yield amounts to from 0,5 p.c. to more than p.c; from lupulin up to 3 p. c. The latter, however, possesses a less agreeable odor, and hence is of inferior quality. The aqueous distillate, more particularly that of the lupulin, is strongly acid and contains valeric acid (Personne), and probably also butyric acid (Ossipoff).
Hops which have been bleached with sulphur should not be used for distillation, otherwise the oil will have an unpleasant odor and contain sulphur.
1) Mededeelingen uit 's Lands Plantentuin 25 (1898), 175.
2) Bulletin du Departement de l'Agriculture aux Indes Neerlandaises 1907, No. 7, 32. Pharmacologic III. Boorsma mentions Celtis reticulata, Miq., as the mother plant, whereas the Index Kewensis enumerates Celtis reticulosa, Miq. = C. cinnamomea, Lindl. = C. reticulata, Torr.
3) Journ. biol. Chem. 5 (1909), 489; Apotheker Ztg. 24 (1909), 885.
Properties. Oil of hops is a light-yellow to reddish-brown, thin liquid which becomes viscid upon prolonged standing. It has an aromatic odor and a non-bitter taste. d15o 0,8551) to 0,893; aD almost inactive or but slightly Iaevogyrate or dextrogyrate; nD20o1,4852 to 1,4914; A.V.0,5 to 10; E.V. 15 to 40; E.V. after acetylation (one determination) 74,0. In alcohol the oil is difficultly soluble. Older oils at times yield no clear solution with even 95 p.c. alcohol, due possibly to the polymerization product of the myrcene contained in the oil.
Composition. Although oil of hops has early been subjected to investigations2), nevertheless these did not result in the isolation and identification of a single constituent. However, the presence of several hydrocarbons and oxygenated substances has been established by more recent investigations.
In the lowest boiling fractions, A. C. Chapman3) found dipen-tene as well as a less dense myrcene-like, olefinic hyrocarbon. When hydrated according to Bertram and Walbaum, it yielded an ester of a lavender-like odor.
Later F.W. Semmler and W.Mayer4) demonstrated that the hydrocarbon in question is myrcene, by converting it into dihydro-myrcene and into tetrabromodihydromyrcene, the latter melting at 87 to 88°, furthermore by its conversion into myrcenol.
In the middle fraction Chapman3) found linalool and a volatile acid C9H18O2, probably isononylic acid, as ester. The presence of a geranyl ester was suspected.
Almost two thirds of the oil of hops consist of a sesquiterpene that boils between 263 and 266° and has a specific gravity of 0,900 at 15°. Upon fractionation it is obtained either slightly laevogyrate or dextrogyrate; when perfectly pure it presumably is optically inactive. Chapman5) obtained derivatives of this sesquiterpene, similar to those of caryophyllene, but not identical therewith. Hence he regarded it as a new hydrocarbon and named it humulene.
1) A. C. Chapman (Journ. chem. Soc. 83 [19C3], 505. - Pharm. Review 81 , 155) observed d15/15o 0,8403 in connection with one oil.
2) Payen & Chevallier, journ. de Pharm 8 (1822), 214 and 533. - R.Wagner, Journ. f. prakt. Chem. 58 (1853), 351. - J. Personne, Compt. rend. 38 (1854), 309. - G. Kuhnemann, Berl. Berichte 10 (1877), 2231; Chem. Zentralbl. 1878, 573. - J.Ossipoff, Journ. f. prakt. Chem. II. 28 (1833), 447; 34 (1886), 238.
3) Journ. chem. Soc. 83 (1903), 505.
4) Berl. Berichte 44 (1911), 2009.
5) Journ. chem. Soc. 67 (1895), 54 and 780.
By means of the nitrosochloride and nitrosate, E. Deussen1) succeeded in demonstrating that humulene consists in the main of i- a -caryophyllene, with which is admixed some B-caryo-phyllene2).
Upon oxidation of oil of hops with chromic acid mixture, Chapman3) obtained succinic acid and asymmetric dimethyl succinic acid in addition to volatile acids (acetic acid and homo-logues).
Adulteration. As adulterants of oil of hops the oils of copaiba balsam and gurjun balsam are mentioned. Both can be detected without difficulty. In one instance the addition of gurjun balsam was observed by Schimmel & Co.4). The oil in question had a specific gravity of 0,9189 (15°) and an optical rotation of - 40°40'; besides, its solubility was not as good as commonly met with in hop oils. The differences observed upon fractionation are also noteworthy: a pure oil yielded fractions which were but slightly optically active; the adulterated oil yielded fractions with a rotation up to - 86° 50'.
From the behavior recorded above, also from the greenish though slight fluorescence, the conclusion could be drawn with certainty that the oil had been adulterated with very appreciable amounts of gurjun balsam.