Cineol (eucalyptol), C10H18O, is very widely distributed. It is the principal constituent of the oil of Eucalyptus Globulus, of cajeput oil, niaouli oil and of the oil of wormseed. In varying amounts it has also been found in American wood turpentine oil, Java "lemon olie", safran oil, oil of zedoary oil of galangal, ginger oil, oil of paradise grains (?), Ceylon, Bengal, Malabar and Kamarun cardamom oil, in the oil from the fruit of Amomum Mala, in matico oil, betel oil, star anise oil, in Japanese star anise oil, magnolia oil, kobuschi oil, boldo leaf oil, camphor oil, in the oil from the leaves of Laurus Camphora, in cinnamon root oil, in the bark oil from Cinnamomum Oliver/, in nikkei oil, in apopin oil, in laurel leaf oil, in the oil of laurel berries, in the leaf oil from Tetranthera polyantha var. citrata, in the oil of Umbellularia californica, in the bark oil of Ocotea usam-barensis, in kuromoji oil, in carqueja oil, in the oils of rue, canella alba, myrtle, cheken leaf, and pimenta, in the oils of Melaleuca acuminata, M. linariifolia, M. nodosa, M. thymifolia and M. uncinata, in the oils of Eucalyptus acmenioides, E. affinis, E. albens, E. amygdalina, E. angophoroides, E. apiculata, E. Baeuerleni, E. Behriana, E. bicolor, E. Bosistoana, E. bo-tryoides, E. bridgesiana, E. Cambagei, E. camphora, E. capitel-lata, E. carnea, E. cinerea, E. cneorifolia, E. conica, E. cordata, E. coriacea, E. corymbosa. E. crebra, E. Dawsoni, E. dealbata, E. dumosa, E. eugenioides, E. fastigata, E. fraxinoides, E. gonio-calyx, E. gracilis, E. haemastoma, E. hemilampra, E. hemiphloia, E. intermedia, E. lactea, E. longifolia, E. Luehmanniana, E. mac-rorhyncha, E. maculata, E. maculosa, E. Maiden/', E. melano-phloia, E. melliodora, E. microcorys, E. microtheca, E. Morrisii, E. nigra, E. obiiqua, E. odorata, E. oleosa, E. oreades, E. ovali-folia, E. o. var. lanceolata, E. paludosa, E. paniculata, E. pen-dula, E. piperita, E. polyanthema, E. polybractea, E. populifolia, E. propinqua, E. pulverulenta, E. punctata, E. p. var. didyma, E. quadrangulata, E. radiata, E. resinHera, E. Risdoni, E. robusta, E. Rossei, E. rostrata, E. r. var. borealis, E. rubida, E. saligna, E. siderophloia, E. sideroxylon, E. s. var. pallens, E. Smithii, E. squamosa, E. stricta, E. Stuartiana, E. tessellaris, E. tereti-cornis, E. t. var. linearis, E. trachyphloia, E. umbra, E. vim in alt's, E. v. var. a virgata, E. viridis, E. vitrea, E. Wilkinsoniana and E. Woolsiana, in the oils from the leaves of Vitex Agnus Castus, and V. trifolia, in the oils of rosemary, lavender and spike, also in the oils of Lavandula dentata, L pedunculata, L Stoechas, in sage oil, in Spanish majoran oil, in American, French and Russian peppermint oils, in spearmint oil, in Java- and Reunion basilicum oil, in the oils of Blumea balsamifera, Osmitopsis asteriscoi-des(2), Achillea millefolium, A. moschata, Artemisia vulgaris, A. frigida, A. Herba-alba, A. Leudoviciana and in yomugi oil.
The preparation of this substance from oils, such as the oil of Eucalyptus Globulus rich in cineol is not difficult, since the cineol, purified as carefully as possible by fractional distillation, crystallizes in the cold. For the identification or isolation of small amounts of cineol, the hydrogen chloride addition product, or better still that with hydrogen bromide, is resorted to. Upon decomposition with water both yield cineol.
Pure cineol is a colorless, optically inactive liquid, the odor of which resembles that of camphor and which crystallizes in the cold. For the cineol regenerated from its chlorhydrate, Wallach1) observed the following constants:
B. p. 176; d20o 0,9267; nD 1,45839.
In connection with products obtained on a technical scale, Schimmel & Co. observed:
Congealing point about +1°; m. p. between + 1 and 1,5°; b. p. 176 to 177° (764 mm.); d15o0,928 to 0,930; nD20o1,456 to 1,459; soluble in about 12 vol. of 50 p. c, in 4 vol. of 60 p. c. and in 1,5 to 2 vol. of 70 p. c. alcohol.
Cineol yields characteristic, loose addition products with bromine, iodine, chlorine and hydrogen bromide,-) phosphoric acid, arsenic acid, a- and /i-naphthol, iodol and resorcinol. Some of them can be utilized for isolating and characterizing cineol. The resorcinol compound is also adapted to the quantitative determination of cineol. (Compare the chapter "The examination of volatile oils".) Dehydrating agents convert cineol into dipentene,15)
1) Liebig's Annalen 245 (1888), 195.
2) Liebig's Annalen 225 (1884), 300, 303; 230(1885), 227; 246(1888), 280.
3) Wallach and Brass, Liebig's Annalen 225 (1884), 310.
other suitable reagents convert it directly into derivatives of dipentene. Thus e. g. dipentene dihydriodide results when dry hydrogen iodide is passed into cineol. The oxygen of the cineol is of the oxide type, hence it does not react with hydroxylamine or phenylhydrazine, neither does metallic sodium act on it. Hence cineol can be distilled without decomposition over metallic sodium.
When oxidized with potassium permanganate and the aid of heat, cineol yields the dibasic cineolic acid,1) C10H18O5, m. p. 196 to 197°. Acetic acid anhydride dehydrates this dibasic acid to its anhydride, which, in turn, upon destructive distillation yields methyl heptenone, C8H140, which likewise occurs in nature.
Toward reducing agents cineol is very stable. Molle2) found that hydrogen iodide only will reduce it. When heated with this reagent for an hour in a sealed tube to 220 to 225° with the addition of metallic mercury as iodine binding agent, cineol yielded a hydrocarbon C10H18 (b. p. 165 to 170°; d18o0,8240; aD + 0°; nD 1,45993) which Molle named cineolene, and a polymeric hydrocarbon (C10H16)n.
Cineol has a characteristic odor which usually directs attention to its presence in mixtures. For its ready detection Hirschsohn's3) iodol reaction can be employed. A small amount of iodol is dissolved with the aid of gentle heat in a few drops of the oil to be tested. If cineol be present the equimolecular addition product of the components crystallizes out. Recrystallized from alcohol or benzene this melts at about 1120.4)
If cineol is to be isolated as such, dry hydrogen bromide is passed into the well cooled petroleum ether solution (equal volumes) of the cineol fraction. The white crystalline precipitate resulting is removed by suction and washed with petroleum ether. The hydrobromide thus obtained is fairly stable, melts at 56 to 57°. Water readily breaks it up into cineol and hydrogen bromide.
In the presence of a sufficient cineol content, resorcin can be used to adventage for its isolation. For this purpose the
1) Wallach and Gildemeister, Liebig's Annalen 240 (1888), 268.
2) Uber die Zusammensetzung des atherischen Lorbeerdles und zur Kenntnis seines Hauptbestandteils, des Cineols, Inaug.-Dissert. Basel 1904, p. 62. Comp. also Thorns and Molle, Arch, der Pharm. 242 (1904), 181.
3) Pharm. Zeitschr. f. Russland 32 (1893), 49, 67.
4) Bertram and Walbaum, Arch, der Pharm. 235 (1897), 178 cineol fraction is stirred with two volumes of a 50 p. c. resorcinol solution. If necessary a small amount of cineol resorcinol is added. The resulting addition product, consisting of 1 mol. resorcinol and 2 mol. cineol,1) is removed by suction, pressed between filter paper and decomposed with alkali. Cineol resorcinol crystallizes in needles that melt at about 80°. They are readily soluble in alcohol, ether and benzene, but very difficultly in petroleum ether and water. It is relatively much more stable than the addition product of phosphoric acid to cineol, which is also used for the isolation of the latter. However, it also decomposes gradually with the liberation of cineol when exposed to the air - more readily in vacuum - so that finally resorcinol alone remains. The same change can be observed when cineol resorcinol is heated with water or petroleum ether,2) or even when the compound is washed with these solvents. Dry and well crystallized, cineolresorcinol can be obtained by crystallizing 1 part of resorcinol from 10 parts of cineol (Baeyer and Villiger, loc. at).
For further characterization cineol can be oxidized with potassium permanganate to cineolic acid.
Cineol possesses antiseptic properties. In medicine it finds external as well as internal application, the latter e. g. as vermifuge. Toxic results have been observed in connection with cineol or eucalyptus oils only then when larger amounts were administered.
The only other oxide found in volatile oils is the Carlina oxide, C13H10O, which constitutes the principal constituent of the carline thistle. It is probably phenyl-l-a-furyl-3-allene.3)
B. p. 167 to 168° (20 mm); d 17o/17o1,066; aD + 0°; nD 1,586.
When oxidized with potassiumpermanganate, it yields quantitatively benzoic acid; when reduced with sodium and alcohol, tetrahydrocarlina oxide, C13H14O, which is oxidized by potassium permanganate to y-phenylbutyric acid, m. p. 52°.
1) Baeyer and Villiger, Berl. Berichte 35 (1902), 1209.
2) Report of Schimmel & Co. October 1907, 47.
3) Semmler, Berl. Berichte 39 (1906), 726; Semmler and Ascher, Ibidem 42 (1909), 2355.