A positive proof for the occurrence of fenchene in volatile oils has not yet been brought. The inference of its presence in terpene fractions boiling about 160° has been drawn from the formation of fenchyl alcohol. Thus Bouchardat and Tardy1) obtained from an oil of Eucalyptus Globulus a terpene which, when heated with benzoic acid, yielded fenchyl alcohol. Upon heating French turpentine oil with sulphuric acid (1/10 of its weight), and the reaction product with an excess of alcoholic potassa in an autoclave to 150°, these same authors obtained a readily soluble potassium salt which, upon addition of water, broke up into potassium acid sulphate and tf-fenchylalcohol.2) When repeating this experiment, Schimmel & Co., however, could not find this alcohol.3) In as much as it is not impossible that this terpene may occur as such in nature, mention of these observations should here be made.
Artificially fenchene has been obtained by the dehydration of fenchyl alcohol, also by splitting off hydrogenchloride from fenchyl chloride.4) Synthetically it has also been obtained from nopinone, an "Abbau" product of B-pinene.5) Upon diazotation of fenchylamine with nitrous acid, Wallach6) obtained, in the main, a fenchene which boiled at 156 to 157°; d19o 0,869; aD - 32° 12'; nD19o1,4729.
The isomeric complexities are even greater in the case of the fenchenes than in that of the camphenes. Possibly not one of the fenchenes thus far obtained represents a chemical unit. Even when the method of preparation employed was the same, differences in the constants, more particularly in the angle of rotation, were observed. In addition to semicyclic fenchenes, there appear to be fenchenes with double linkage in the cycle, the boiling point of which is appreciably lower. Fenchene has thus far been obtained only in the liquid state. Its odor reminds of that of camphene. The following constants have been determined:
1) Compt. rend. 120 (1895), 1418.
2) Compt. rend. 125 (1897), 113.
3) Report of Schimmel & Co. April 1904, 53.
4) Wallach, Liebig's Annalen 263 (1891), 149.
5) Wallach, Ibidem 357 (1907), 53; 363 (1908), 3. 6) Ibidem 362 (1908), 180.
B. p. 154 to 155°; d18o 0,8660; nD18o1,4693.
B. p. 155 to 156°; d18o 0,8670; nDl8o 1,47047;1) aD + 21°.2)
Repeated determinations in the laboratory of Schimmel & Co. revealed the following constants:
B. p. 154 to 156° (765 mm.); d15o 0,8660 to 0,8665; nD16o 1,46733 to 1,46832.
From the /-fenchene ([a]D- 32° 12') mentioned above, Wal-lach3) prepared a dextrogyrate dibromide which melted at 87 to 88° and which revealed a specific rotation of -+ 42,83°. A dibromide prepared from (d-fenchene (the fenchene being obtained from /-fenchone from thuja oil) likewise melted at 87 to 88°. A mixture of equal parts of both bromides, upon recrystallization, showed the melting point 62°.4)
No other characteristic halogen or hydrohalogen or nitrosyl-chloride addition products are obtainable that might be used for the identification of fenchene. However, in like manner as camphene, fenchene can be hydrated to C10H18O by means of the glacial acetic acid and sulphuric acid mixture. The alcohol thus obtained is isofenchyl alcohol (m. p. 61,5 to 62°) which yields with phenylIsocyanate a phenylurethane melting at 106 to 107°.5)
From the semicyclic fenchenes there result, upon oxidation with potassium permanganate, hydroxyfenchene acids which are characterized by difficultly soluble sodium salts.