Oleum Piperis. - Pfefferol. - Essence de Poivre.
Origin. The unripe, picked and dried berries of Piper nigrum, L. (family Piperacese), a climbing shrub, which was originally indigenous to southern India, constitute the black pepper of commerce, whereas white pepper consists of the fully matured berries deprived of their outer shell. Pepper is cultivated in southern India, in numerous islands of the Indian archipelago, in the Philippines and the West Indies.
Preparation. Black pepper contains 1 to 2,3 p. c. of volatile oil, which is obtained by steam distillation of the comminuted fruits. Noteworthy in this connection is the formation of ammonia which is also observed during the distillation of several other oils, e.g. ginger, pimento, and cubeb oils.
White pepper, also the shells removed in the preparation of white pepper, contain volatile oil1). Whether this corresponds in its properties with that of the black pepper is not known.
1) Luca (Trommsdorff's Taschenbuch fur Chemiker und Pharmaceuten 182*2, 81) obtained 1,61 p. c. of oil from white pepper.
Properties. A colorless to yellowish-green liquid with a more or less decided phellandrene odor and a mild, by no means pungent taste, d15o 0,87 to 0,916. Polarized light is deviated either to the left or right; aD - 10 to +3°; n20o1,489 to 1,499. In alcohol pepper oil is difficultly soluble, 10 to 15 vol. of 90 p. c. alcohol being required to form a clear solution. On account of the large phellandrene content, the phellandrene reaction with sodium nitrite and glacial acetic acid yields direct results without previous fractionation.
Composition. As shown by the earliest analyses1), pepper oil is well-nigh free from oxygen. This result was substantiated by the investigation of L. A. Eberhardt2), whose elementary analysis of the oil yielded 87,26 p. c. carbon and 10,81 p. c. of hydrogen. The last fractions of the oil distilling over between 170 to 310° were green in color. Fraction 169,5 to 171° had the composition of a terpene. The fraction boiling at about 176° yielded terpin hydrate when treated with alcohol and acid.
Later, Schimmel & Co. found phellandrene in pepper oil3), judging from the laevorotation of the fraction (aD - 10°) from which the nitrite had been prepared, it may be concluded that the phellandrene of pepper oil is /-phellandrene.
The preparation of the tetrabromide showed that fraction 176 to 180° examined by Eberhardt contained dipentene. It is questionable, however, whether dipentene is an original constituent of the oil, or whether it has resulted from phellandrene upon repeated fractionation4).
It also remains undecided to which terpene the terpin hydrate owes its origin. That dipentene may be converted into terpin hydrate is known. Whether phellandrene can be converted into terpin hydrate under suitable conditions has not yet been investigated.
1) An analysis of the oil by Dumas (Liebig's Annalen 15 , 159) agreed with the formula C10H16; compare also Soubeiran and Capitaine, Liebig's Annalen 34 (1840), 326.
2) Arch, der Pharm. 225 (1887), 515.
3) Report of Schimmel & Co. October 1890, 49.
4) With regard thereto Wallach makes the following statement (Liebig's Annalen 287 , 372): Phellandrene-containing oils should not be fractionated at all, or at least not repeatedly, under ordinary pressure, since the hydrocarbon suffers changes when submitted even to this treatment.
From pepper oil O. Schreiner and E. Kremers1) have isolated a sesquiterpene, the physical constants of which agreed with those of caryophyllene. The proof of their identity was supplied by producing the nitrosite melting at 43°.
In the highest boiling fractions H. Haensel2) found a sub-stance that melted at 138°.