Thus far this terpene has been obtained by synthetical means only, although Clover1) claims to have found it in a Manila elemi oil, observing at the same time a gradual inversion into dipentene. Recently its presence in coriander oil has likewise been rendered probable.2)
The boiling point of terpinolene is in the neighborhood of about 185 to 187°. As characteristic derivatives, the tetrabromide melting at 116° and the dibromide melting at 69 to 70° should be mentioned. The addition of hydrohalogen yields the corresponding dipentene derivatives. Upon oxidation with potassium permanganate, terpin-olene erythritol, C10H16(OH)4H2O, melting at 148 to 150°, results.
Sylvestrene (i-Sylvestrene = Carvestrene).
Sylvestrene is one of the less common natural terpenes. Thus far it has been found, always in the dextrogyrate modification, in the oils of the Pinaceae: in the pine tar oils of Sweden and Finland, in the turpentine oils of Finland, Russia, and Sweden, in the needle oil of Pinus sylvestris of Germany, Sweden, and England, in the needle oil of Pinus montana, and in cypress oil. The statement by More1) that /-sylvestrene occurs in the oil from the resin of Dacryodes hexandra, still needs verification.
1) Philippine Journ. of Sc. 2 (1907), A. 17. 2) Report of Schimmel & Co. October 1909, 48.
It can be obtained in a relatively pure state by preparing the dichlorhydrate from fractions rich in sylvestrene and by subsequent regeneration by boiling the hydrochloride either with aniline2) or with sodium acetate and glacial acetic acid.3) The hydrocarbon thus obtained closely resembles limonene in its physical and chemical properties. Like the limonene, it has a pleasant odor resembling that of limonene. Specific gravity and boiling point agree well with the corresponding constants of limonene.
Atterberg, the discoverer of sylvestrene, found the following constants:
B. p. 173 to 175°; d16o 0,8612; [a]D16o + 19,5°.4)
Wallach records the following:
B. p. 176 to 177°; d16o0,851; nDl,47799.5)
B. p. 175 to 176°; d20o 0,848; [a]D + 66,32° (in chloroformic solution); nD 1,47573.6)
When heated to 250°, sylvestrene is polymerized, but not isomerized, neither is the latter change brought about by alcoholic sulphuric acid. Hence this hydrocarbon is one of the most stable of the terpene group. Like limonene, so sylvestrene contains two double bonds that can be satisfied either entirely or in part by hydrohalogen, bromine, or nitrosyl chloride. Peculiar, however, is the dichlorhydrate which, unlike the inactive dipen-tene dihydrochloride, is optically active (dextrogyrate) and from which active sylvestrene can be regenerated upon splitting off hydrohalogen. The tetrabromide, prepared like that of the limonene, melts at 135 to 136°; however, it is difficult to obtain it in solid state when, as is mostly the case, other terpenes are present in the fraction. With amyl nitrite and hydrochloric acid, pure sylvestrene yields a nitrosochloride melting at 106 to 107°, and this with benzylamine an nitrolamine base that melts at 71 to 72°.
1) Journ. chem. Soc. 75 (1899), 718,
2) Wallach, Liebig's Annalen 230 (1885), 243.
3) Wallach, Liebig's Annalen 239 (1887), 25; 245 (1888), 197.
4) Berl. Berichte 10 (1877), 1206.
5) Liebig's Annalen 245 (1888), 198. 6) Liebig's Annalen 252 (1889), 149.
For the separation of sylvestrene from mixtures, as well as for its identification, the chlorhydrate is best suited. This compound, which can be separated in crystalline form at considerably reduced temperatures only, is prepared in the following manner. The fraction in question is diluted with an equal volume of ether and saturated with hydrogen chloride gas. After standing for about two days, the ether is distilled off and the residue induced to crystallize by considerably reducing its temperature. With the aid of porous plates the crystalline magma is freed from oily admixture and recrystallized from an equal weight of alcohol. The hydrochloride thus partly purified, is freed from the corresponding dipentene compound by fractional crystallisation from ether, in which the latter is more difficultly soluble. The purified dihydrochloride melts at 72V) It should be remembered that, in the presence of dipentene or of such terpenes that yield dipentene dihydrochloride when acted upon by hydrogen chloride, mixtures of chlorhydrates result, the melting point of which is lowered with the increasing content of dipentene dihy-drochloride. The dibromohydrate of sylvestrene melts at 72°, the diiodohydrate at 66 to 67°. By treating these dihalogen hydrates with dilute potassium hydroxide, sylveterpin, C10H18(OH)2, m. p. 135 to 136°, also sylveterpineol, C10H17OH, b. p. 210 to 214°,2) result. These compounds correspond with those obtained in like manner from dipentene dihydrochloride.
If to a solution of a few drops of sylvestrene in acetic acid anhydride a drop of concentrated sulphuric acid be added, a beautiful blue color is produced. This reaction succeeds only then when the fraction to be tested is rich in sylvestrene.
1) Wallach, Liebig's Annalen 230 (1885), 241; 239 (1887), 25. 2) Wallach, Liebig's Annalen 357 (1907), 72.