The lowest member of the limit series of hydrocarbons CnH2n + 2 which has been found in volatile oils is the normal heptane," C7H16 (b. p. 98,5 to 99°; d15o 0,6880). In addition to minimal amounts of other substances, it has been obtained by the distillation of the oleoresin of Pinus Sabiniana and P. Jeffreyi, both of which are found in California, also by the distillation of the fruits of Pittosporum resiniferum.
The higher members of the paraffin, and probably of the olefin series also, appear to be quite widely distributed in the vegetable kingdom. They constitute the wax-like coating and secretions on leaves, flowers, fruits etc. In volatile oils, however, they are not met with commonly because of their sparing volatility. Sometimes they separate in crystalline form when the oil is exposed to a low temperature, or they remain behind upon fractional distillation. In the oils of rose and chamomile, however, the amount of paraffin is so large, that the oil congeals even at middle temperature. Apparently these hydrocarbons seldom occur alone, but as mixtures of homologues as has been shown in the case of rose oil. Their melting points seldom if ever agree with those of known members of the series. With the exception of the heptane referred to, they are obtained principally as white, colorless, laminar-crystalline masses which are with difficulty soluble in cold alcohol, but readily soluble in hot alcohol and other organic solvents. They are remarkable on account of their stability toward concentrated acids and oxidizing agents at ordinary temperatures.
The rose oil stearoptene melts at 35° and, when distilled in a vacuum, can be resolved into two fractions melting at 22° and 40 - 41° respectively. In addition to this solid mixture, paraffin (or olefin) hydrocarbons have been found more particularly in the oils distilled from flowers. The paraffins thus far isolated are recorded, with their melting points, in the following table:
Oil of Kaempferia Galanga.........m. p. 10°
Oil of poplar buds, a mixture of homologous paraffins with the melting points 53 to 54°, 57 to 58°, 62 to 63°, 67 to 68°
Oil of birch buds...............m. p. 50°
Oil of hemp..................m. p. 63 to 64°
Oil of sassafras leaves............m. p. 58°
Oil of pelargonium..............m. p. 63°
Oil of jaborandi leaves............m. p. 28 to 29°
Oil of neroli (aurade).............m. p. 55°
Oil of Evodia simplex............m. p. 80 to 81°
Oil of several Cistus species........m. p. 64°
Oil of dill................... m. p. 64°
Oil of wintergreen (both Betula and Gaul- theria).................m. p. 65,5°
Oil of verbena.................m. p. 62,5°
Oil of Helichrysum angustifolium.....m. p. 67°
Oil of Roman chamomile..........m. p. 63 to 64°
Oil of German chamomile..........m. p. 53 to 54°
Oil of Chrysanthemum cinerariaeiolium . m. p. 64° Oil of arnica flowers . . ...........m. p. 63°
Additional occurrences of the paraffins have been established in the oils from species of Spiraea and Turnera, in oil of chervil, in the oil of elderblossoms, the oils of Monarda didyma, of Inula viscosa and others.
Of olefinic hydrocarbons, the octylene, C8H16 (m. p. 123 to 124°; d 0,7275; nD 1,4066) only has been found thus far, viz., in the oils of bergamot and lemon. Possibly it also occurs in lignaloe oil. Isoprene, C5H8, interesting because of its relation to the terpenes, has been observed only as decomposition product of caoutchouc and turpentine oil.
However, chain hydrocarbons of the formula of saturation CnH2n_4 with three double bonds have been found. In composition they agree with the terpenes but differ in having a lower specific gravity and a lower index of refraction. These hydrocarbons, which have been termed "olefinic terpenes" by Semmler, show a great tendency to resinify, especially when distilled under ordinary pressure.
The first representative of this class was found in oil of bay by Power and Kleber1) and named myrcene. Later its presence in the first fractions of the oil of Lippia citriodora was ascertained. Probably it also occurs in West Indian lemongrass oil and in oil of lignaloes. Barbier found myrcene among the dehydration products of linalool. Its constitution has not yet been definitely determined, but probably finds expression in one of the above formulas. The following constants have been recorded:
b. p. (20 mm)
Power and Kleber1)
67 to 68°
171 to 172°
67 to 68°
166 to 168°
1,4700 (at 19°)
According to Semmler, myrcene, upon reduction with sodium and alcohol, yields dihydromyrcene, C10H18, a liquid possessing the following properties: b. p. 171,5 to 173,5°, d 0,7802, nD 1,4501 (Semmler).1) B. p. 167 to 169° (corr. at 770 mm), d15, 0,7852, nD17o 1,4514 (Enklaar). From the dihydromyrcene Enklaar prepared a tetrabromide melting at 88°.
1) Pharm. Rundsch. (New York) 13 (1895), 61.
2) Berl. Berichte 34 (1901), 3126.
3) Over Ocimeen en Myrceen, Eene Bijdrage tot de kennis van de aliphatische Terpenen. Inaug.-Dissert., Utrecht 1905.
Upon hydration of myrcene with glacial acetic acid and sulphuric acid at 40° according to Bertram's method,1) Power and Kleber obtained an acetate with an odor reminding of lavender. Upon saponification it yielded, in their opinion, linalool. Barbier,2) however, supposed that the hydration yielded a new alcohol which he named myrcenol. From myrcenol Enklaar (I. c.) obtained a crystalline phenylurethane, m. p. 68°, which differs from that obtained from linalool. According to Enklaar, myrcenol has the following constants: b. p. 99° (10 mm), d15o 0,9032, nD15o 1,4806.
Potassium permanganate oxidizes myrcene to succinic acid. Myrcene can be identified by means of the dihydromyrcene mentioned above, also, according to Enklaar, by means of the dihydromyrcen tetrabromide, m. p. 88°. Myrcene polymerises readily to dimyrcene, which is characterized by a nitrosite that decomposes at 163°.