Composition. The first elementary analysis of turpentine oil, referred to on p. 94 of vol. 1, revealed that this oil consists of hydrocarbons C10H16. This conclusion was verified by later investigations. These, however, showed that the turpentine oils may differ physically in so far as some of them deviate the plane of polarized light to the left, others to the right. Berthelot4) named the laevogyrate hydrocarbon terebentene, the dextrogyrate one australene. Wallach5) suggested the name of a-pinene for both modifications and differentiated the two as 1-a-pinene and d-a-pinene.
Among the constituents of turpentine oil the a-pinene predominates to such an extent, that this oil may be regarded as an a-pinene rendered impure by the presence of a few per cent. of other terpenes. The other terpene, the presence of which has been definitely established in turpentine oil, is B-pinene. In addition to pinonic acid, due to a-pinene, A. Baeyer6) obtained upon the oxidation of French turpentine oil an isomeric acid, which melted at 125° and which he named nopinic acid. The formation of this acid he attributes to the hydrocarbon nopinene7), which Wallach named (B-pinene in order to distinguish it from a-pinene. However, it was not until Wallach1) had successfully accomplished the synthesis of B-pinene and after E. Gildemeister and H. Koehler2) had isolated it in a fairly pure condition from hyssop oil, that it could be demonstrated conclusively that this new hydrocarbon is contained in fractions 163 to 166°3) of turpentine oil. For its properties see vol. 1, p. 298.
1) Vezes, Sur la definition de l'essence de terebenthine commerciale-ment pure, Bordeaux 1910, p. 8.
2) Ibidem p. 9.
3) Ibidem p. 10.
4) Compt. rend. 55 (1862), 496 and 544. - Liebig's Annalen Suppl. II. (1862/63), 226.
3) Liebig's Annalen 227 (1885), 300; 356 (1907), 227.
6) Berl. Berichte 29 (1896), 25.
7) Semmler's pseudopinene. Berl. Berichte 33 (1900), 1458.
Judging from experience thus far, American turpentine oil appears to be richer in B-pinene than the French oil. Nevertheless it contains only a few percent. It is noteworthy that both turpentine oils contain the same 1-B-pinene.
In order to demonstrate the presence of B-pinene, it is oxidized to nopinic acid as described in vol. I, p. 299. For this purpose Schimmel & Co.4) utilized the last fractions obtained in the rectification of turpentine oil, 30 grams of a fraction, b. p. 161,5 to 162,5 under 753 mm. (d15o 0,8690; aD - 0°14'; nD20o 1,47322), when oxidized with permanganate in the presence of free sodium hydroxide, yielded upon concentration of the solutions 4,5 g (= 15 p. c.) of sodium nopinate. 30 g. of a fraction, b.p. 164 to 166° (d15o0,8714; aD - 8°23'; nD20o1,47558), yielded upon like treatment 7,5 g. (= 25 p. c.) of sodium nopinate. When the oxidation mixture was distilled with steam, an oil was recovered that possessed the following constants: d15o 0,8724; aD - 10°59'; nD20o 1,47714. Upon repetition of the oxidation this yielded additional amounts of the difficultly soluble sodium salt. It would seem, therefore, that fraction 164 to 166° consisted largely of ,B-pinene, although the specific gravity was rather high.
Inasmuch as a-pinene is one of the most labile terpenes, it is not surprising to find that some products of decomposition are introduced even during the process of preparation. As already mentioned, the oil contains traces of free acid, such as formic acid, acetic acid and the resin acids. At higher temperatures these act on the pinene with formation of dipentene and polymeric terpenes, both of which are found as companions of the pinene in turpentine oil.
1) Liebig's Annalen 363 (1908), 1 - 19.
2) Wallach-Festschrift, Gottingen 1909, p. 414.
3) Comp. also Ahlstrom & Aschan, Berl. Berichte 39 (1906), 1445. 4) Report of Schimmel & Co. April 1908, 103.
Certain observations and phenomena would seem to indicate that camphene and fenchene are among the normal constituents of turpentine oil. On account of the boiling points of these terpenes, which lie between those of the two pinenes an unobjectionable direct proof of their presence is impossible. However, as will be shown, the indirect proof of the presence of camphene may be considered as established.
In terebene, a product of the action of strong sulphuric acid on turpentine oil, Armstrong and Tilden1) found camphene. They assumed that the camphene had resulted in a manner analogous to its formation from pinene chlorhydrate, a possibility that could not be denied off hand. However, Power and Kleber2) regard it as probable that camphene is originally contained in the turpentine oil and that its presence becomes apparent after the destruction and removal of the pinene.
By the action of sulphuric acid on French turpentine oil and subsequent treatment with alcoholic potassa, the same investigators4) obtained two potassium salts of the formula C10H17Oso2ok. When heated with acids these yielded l-borneol and potassium acid sulphate, and l-fenchylalcohol and potassium acid sulfate respectively. While the formation of these two salts indicates the presence of camphene and fenchene, it does not necessarily follow that the formation of fenchylalcohol is due to fenchene originally present in the oil. It is more likely that the fenchyl alcohol may be attributed to B-pinene, which, as has been shown by Wallach5), is transformed into fenchene very readily. Of the same opinion are Barbier and Grignard6) who have isolated terpineol (obtained from a-pinene) and fenchyl alcohol by the action of glacial acetic acid and benzene sulphonic acid.
1) Berl. Berichte 12 (1879), 1753.
2) Pharm. Rundsch. (New York) 12 (1894), 16.
3) Compt. rend. 113 (1891), 551.
4) Compt. rend. 125 (1897), 111.
5) Liebig's Annalen 363 (1908), 1 to 19.
6) Bull. Soc. chim. IV. 5 (1909), 512, 519.