Oleum Thujae. - Thujaol. - Essence de Thuya.
Origin and Production. Thuja oil is obtained by distillation of the leaves and twigs of the arbor vitae or Thuja occidentalis, L, known in North America as white cedar or swamp cedar. According to E. Jahns2), the yield varies, according to the season, between 0,4 and 0,65 p. c. It is greatest in spring (March) and diminishes greatly in summer (June). The small amount of oil that is demanded for the market is principally distilled in North America where, according to Ayer3), the leaves and branches yield up to 1 p. c. of oil. The oil is distilled primarily in the Northern and Eastern districts of Vermont. Those trees which are exposed to sunlight on all sides are the best. The distillation equipment is frequently very primitive. Care should be taken to pack the still properly so that no free spaces are afforded the steam during distillation. The yield also increases with the steam pressure. At times the oil is water-white, sometimes, when the trees have stood in the shade, it is dark in color. Cold weather does not, however, lower the yield of oil from the leaves, but that from the wood.
1) Baker and Smith, loc. cit. p. 278.
2) Arch, der Pharm. 221 (1883), 749, footnote.
3) Oil, Paint and Drug Reporter June, 1906, 17.
Although it is very different in its properties, the oil of Thuja occidentalis is frequently confounded with that of Juni-perus virginiana, L.
Properties. Thuja oil is colorless or yellow to greenish-yellow in color, limpid, and possesses a strong characteristic, camphor-like odor reminding of male fern, and has a bitter taste. d15o 0,915 to 0,935; aD - 5 to -14°; A. V. 0,6; E. V. 20,6; E. V. after acetylation 41. 1 (one single observation). It forms a clear solution with 3 to 4 parts of 70 p. c. alcohol. It boils between 160 and 250°, the bulk of the oil distilling between 180 and 205°. The first fraction contains acetic acid1) with little formic acid.
Composition. Thuja oil was first examined in 1843 by Schweizer2), however, without any definite results. More successful was Jahns3) who succeeded in isolating three constituents by fractional distillation. He obtained a dextrogyrate terpene fraction which boiled between 156 and 161°, a dextrogyrate fraction which boiled between 195 and 197°, and a Iaevogyrate fraction which boiled between 197 and 199°. The latter fractions contained oxygen and corresponded to the formula C10 H16 O. Inasmuch as they appeared to be optically isomeric, they were designated /- and d-thujol.
The later investigations by Wallach4) definitely cleared up the situation. The identity of the terpene of fraction 160° with d-a-pinene (nitrosochloride) was established. The fraction up to 190° contains a substance that is acted upon by potassium hydroxide with the formation of potassium acetate. Presumably it is an acetic ester. Fraction 190 to 200° contains two chemically distinct ketones of the formula C10 H16 O, viz. /-fenchone and d-thujone.
1) Jahns, loc. cit.
2) Journ. f. prakt. Chem. 30 (1843), 376. - Liebig's Annalen 52 (1844), 398.
3) Loc. cit.
4) Liebig's Annalen 272 (1892), 99.
From the fraction distilling about 220°, Wallach1) obtained an inactive oxime that melted at 93 to 94° and which proved to be a derivative of carvotanacetone2). Inasmuch as Semmler3) had shown that thujone, when heated to higher temperatures, is converted into carvotanacetone, it is probable that carvotan-acetone is not present as such in the oil but results from the thujone upon fractional distillation.
While preparing the semicarbazone of /-fenchone from thuja oil, Wallach4) later found that this fenchone, which had been treated with nitric acid for the purpose of removing thujone, contained /-camphor. This discovery led to a renewal of the investigation of thuja oil which revealed that it does not contain camphor but /-borneol or its ester. When the oil was treated in the conventional manner for the isolation of fenchone, the borneol was oxidized to /-camphor.