The best known representative of this subgroup as of the group of the sesquiterpenes in general is the cadinene, which is widely distributed and which occurs in both optical modifications.
1) Berl. Berichte 39 (1906), 652.
2) Pharmaceutical Journ. III. 12 (1882), 243.
3) Pharm. Ztg. 45 (1900), 414.
4) Pharmaceutical Archives 4 (1901), 63; Chem. Zentralbl. 1901, II. 1226.
In most of the references on the occurrence of cadinene, the direction of the rotation is not mentioned, thus in German and Swedish oils from Pinus sylvestris, the oils from Pinus montana, of Picea excelsa, juniper berries, savin, cedar leaves, cedar wood, lemongrass, pepper, betel, ylang-ylang, camphor, Amorpha fruticosa, frankincense, African copaiba balsam (see below!), asafetida, galbanum, American peppermint, patchouli, wormwood and goldenrod.
Cadinene can be obtained in a relatively pure condition since it yields a well crystallized dihydrochloride from which it can be regenerated, like the terpenes, by heating with aniline or with sodium acetate in glacial acetic acid solution.1) For the hydrocarbon thus regenerated, Wallach found the following constants:
B. p. 272° (uncorr.)2), 274 to 275°; d20o 0,918; [a]D - 98,56°; nDl,50647.3)
Schimmel & Co. found:
B. p. 271 to 273°; d15o 0, 9215; [a]D - 105° 30'.
The optical rotation varies considerably. In a number of instances where the natural sesquiterpene has been pronounced an active modification of cadinene, it has not been definitely established whether the hydrocarbon is really identical with cadinene, or whether it has been converted into a cadinene derivative by the action of hydrogen chloride. This is true e. g. of the sesquiterpenes in West Indian sandalwood oil and African copaiba balsam. It is at least noteworthy that a derivative of /-cadinene should have been obtained from these dextrogyrate oils, whereas the dextrogyrate hydrocarbon from Atlas cedar oil yielded derivatives of tf-cadinene.
1) Wallach, Liebig's Annalen 238 (1887), 84.
2) Liebig's Annalen 271 (1892), 303.
3) Ibidem 252 (1889), 150; 271 (1892), 297.
When exposed to air, cadinene resinifies very readily with the formation of a polymerization product. When heated for a long time with dilute sulphuric acid, cadinene is altered, whereas the action of hydrohalogen appears to produce no essential change since the optical activity remains unaltered. Prolonged heating to 200° likewise changes cadinene. An isomeric hydrocarbon is thus produced with the following properties: b. p. 145 to 148° (20 mm); d 20o/4o,9061; [a]D - 2,80°; nD20o 1,5041.1)
With nitrosyl chloride and nitrogen tetroxide, cadinene yields crystalline addition products. The nitrosochloride, of which only a small yield is obtained, melts at 93 to 94°; the nitrosate, which affords a better yield, melts at 105 to 110°.
Especially characteristic are the crystalline addition products obtained with two molecules of hydrohalogen, of which the dichlor-and the dibromhydrate are used for identification.
For the purpose of preparing the dichlorhydrate, fractions 260 to 280° are diluted with twice their volume of ether, well cooled and saturated with hydrogen chloride. After prolonged standing, the ether is in part distilled off, in part allowed to evaporate spontaneously. The crystals of dichlorhydrate thus obtained are dried on porous plate, washed with alcohol to remove oily impurities and recrystallized from acetic ether in which they can readily be dissolved with the aid of heat. The pure compound melts at 117 to 118°. It is optically active, [a]D - 37° 27' in a 5 p. c. chloroform solution.
The dichlorhydrate can also be prepared with the aid of glacial acetic acid that has been saturated with hydrogen chloride. This modification is especially adapted to the preparation of the dibromhydrate (m. p. 124 to 125°) and the diiodhydrate (m. p. 105 to 106°). The glacial acetic acid solution of the hydrohalogen is added to the glacial acetic acid solution of the hydrocarbon.