Simultaneously with citronellal there passes over during the fractional distillation a substance that solidifies in the receiver and that has been identified as l-borneo/1) (m. p. of phenyl-urethane 138°). In addition there occurs a substance with linalool-like odor which upon oxidation yields citral (m. p. of citrylidene cyanacetic acid 120 to 121°) but which, contrary to an opinion previously expressed2), does not appear to be linalool.
In a fraction 218 to 230°, from which the borneol had been removed as completely as possible, the presence of small amounts of nerol (m. p. of tetrabromide 116 to 118°) has been demonstrated3). The next fraction which constitutes an appreciable portion of the oil, consists of geraniol4). This alcohol can be separated by treating this fraction with calcium chloride and decomposition of the purified calcium chloride geraniol with water. Further distillation yields an oil that consists of a mixture of esters of d-c/tronellol and geraniol. Citronellol (m. p. of the silver salt of the acid phthalate 125 to 126°) does not occur as such but as acetate and probably also as n-butyrate. Geraniol occurs as acetate3).
The highest boiling fractions contain methyleugenol5) which was identified by its oxidation to veratric acid (m. p. 179°) with potassium permanganate and by its conversion into methyliso-eugenol (m. p. of dibromide 102°).
If the highest boiling fractions referred to are shaken repeatedly with 70 p. c. alcohol in order to remove the methyl-eugenol and if the residual oil is redistilled, there finally result two fractions which consist chiefly of sesquiterpenes6). The lower boiling fraction of the two, which, however, was not perfectly free from oxygen, had the following properties: b.p. 157° (15 mm.); d15o.0,8643; aD + l°28'; nD15o. 1,51849. Under ordinary pressure this substance boiled between 270 and 280°, however, with considerable decomposition. When shaken with dilute permanganate solution in the cold, carbonic acid, oxalic acid and a glycol-like substance, insoluble in water, resulted. The odor of the sesquiterpene is peculiar and reminds of cedarwood. Hydration with glacial acetic acid-sulphuric acid (0,1 p.c.) mixture yielded a product the saponification value of which was not higher than 43,6. Inasmuch as it appeared greatly resinified it did not invite further investigation. When exposed to the air for but a day, resinification took place and a syrupy liquid resulted that was not soluble in even 10 vols, of 95 p.c. alcohol.
1) Report of Schimmel & Co. April 1912, 47.
2) Ibidem October 1899, 21.
3) Ibidem April 1912, 47.
4) Ibidem October 1893, 15.
5) Ibidem October 1898, 11; October 1899, 24. 6) Ibidem October 1899, 24.
The entire behavior and the low specific gravity of the sesquiterpene suggest an aliphatic sesquiterpene (see vol. I, p. 328).
From the higher fraction of the two, careful fractionation under diminished pressure yielded a second sesquiterpene with the following properties: b. p. 272 to 275° under 760 mm., 170 to 172° under 16 mm. pressure; d15o0,912; aD + 5°50'. Owing to the slight difference in the boiling point, it was not possible to free this substance entirely from the light sesquiterpene.
Finally, it may be mentioned that Schimmel & Co. made an observation that seems to indicate the presence of thujyl alcohol. When the fraction rich in the substance with a linalool-like odor (see p. 227) was oxidized with chromic acid, there resulted, in addition to citral, a thujone-like substance that yielded a semicar-bazone melting between 179 and 182°. (As to the melting point of the thujone semicarbazones, see vol. I, p. 463.) The attempt to oxidize fraction 202 to 210°, which had the odor of thujyl alcohol with permanganate to thujaketonic acid was unsuccessful1).
Properties. As to their physical properties, the oils of the two citronella grasses differ considerably from each other. The Ceylon citronella oil (Lena batu oil), which constitutes the bulk of the commercial oil, is a yellow to yellowish-brown liquid that is occasionally colored green by copper. Frequently oils that were brown originally become green upon exposure to the air. This change does not take place if the oil has previously been shaken with dilute acids2). The odor of the oil is peculiar and very persistent. Frequently it is characterized as being balm-like, but this comparison is not correct since balm has the odor of citral and not of citronellal, the principal bearer of the Citronella odor. The specific gravity lies between 0,900 and 0,920 and only in exceptional cases does the density of pure oils drop as low as 0,898; aD - 7 to - 22°; nD20o 1,479 to 1,494; the so-called total geraniol content (geraniol + citronellal1)) of good oils is not below 57 p. c. With 1 to 2 vols, of 80 p. c. alcohol the oil yields a clear solution which remains clear upon the addition of more alcohol up to 10 vols., or shows a slight opalescence only. But even in the latter case oily drops never separate upon prolonged standing in stoppered containers.
1) Report of Schimmel & Co. April 1912, 47.
2) Umney, Pharmaceutical Journ. III. 21 (1891), 922.