Origin. The leaf-buds of the black poplar, Populus nigra, L. (family Salicaceae) were formerly kept in apothecary shops under the name of Oculi Populi, and were used in the preparation of an ointment. Upon distillation they yielded about 0,5 p.c. of volatile oil.
Properties. Oil of Poplar buds is pale-yellow to light-brown in color, and has an agreeable odor somewhat suggestive of chamomile. It is insoluble in 70 to 90 p.c. alcohol, but occasionally yields a clear solution with 1/2 vol and more of 95 p.c. alcohol. At times 3,5 to 10 vol. of 95 p.c. alcohol are required, and even then flocculent precipitation of paraffin takes place, d 0,890 to 0,905; aD + 1°54'3) to +6°; A.V.2 to 11; E.V. 8 to 14; E.V. after acetylation 18 to 534).
Composition. Poplar-bud oil distils between 255 and 265°3). According to J. Piccard5) it consists principally of a hydrocarbon (C5H8),X boiling between 260 and 261°. Basing his conclusion on a determination of the vapor density according to Dumas, he regards the compound as a diterpene C20H82.
1) T.Peckolt, Pharm. Rundsch. (New York) 12 (1894), 241. 2) T. Peckolt, ibidem 287.
3) Schimmel's Bericht April 1887, 86.
4) Report of Schimmel & Co. October 1908, 103; October 1912, 95. 5) Berl. Berichte C (1873), 890 and 7 (1874), 1486.
According to the more recent investigations by F. Fichter and E. Katz1), it has been ascertained that the bulk of the oil consists of a fraction 263 to 269°, the vapor density of which, determined according to Victor Meyer with the Lunge gas-volumeter, gave results that agreed with a sesquiterpene C15H24. It was characterized by means of its nitrosochloride, nitrol-piperidine, and nitrolbenzylamine bases, nitrosate, &., all of which were humulene derivatives.
E. Deussen2) has recently demonstrated that humulene is identical with a-caryophyllene, hence this is to be regarded as a constituent of poplar bud oil. Inasmuch as the corresponding fractions of hop oil yield results that are more nearly quantitative than those obtained with poplar bud oil, it is assumed that the latter contains still another sesquiterpene. Moreover, the dextrorotation of the poplar bud sesquiterpene may possibly be attributed to a contamination of the a-caryophyllene with an optically dextrogyrate hydrocarbon.
In addition, poplar bud oil contains about 0,5 p. c. of paraffin melting between 53 and 68°, which is presumably of the formula branches which had been obtained from the neighborhood of Nantes, France. Computed with reference to fresh material he obtained 0,0369 p.c. of oil that had separated from the water. By shaking out the cohobation water, he obtained an additional 0,0083 p. c, making a total of 0,045 p. c. of oil. The oil which had separated of its own accord was greenish-yellow in color, possessed a myrtle-like odor and gave the following constants: d25o0,8984; aD20o - 5°16'; A. V. 3,48; E. V. 15,5; E. V. after acetylation 50,23. It was soluble in one-half volume of 90 p.c. alcohol, but after the addition of 5 vol. the solution became turbid; insoluble in 80 p.c. alcohol. When cooled, the oil became turbid at + 5°, became completely opaque at - 5°, but remained limpid and changed neither appearance nor consistence at - 17°.
The substance that imparts its agreeable odor to the oil passes over with the lower fractions when distilled.