VI. Synthesis with the aid of Grignards reaction.

VII. Ring-formation accompanied by dehydration.

a) from aliphatic terpene alcohols:

Linalool --> Dipentene3) and Terpinene3) Geraniol -► Dipentene.4) b) from aliphatic terpene aldehydes: Citral -► p-Cymene.5)

VIII. Polymerisation of hydrocarbons.

Isoprene -> Dipentene6) Valerylene -> Dipentene.7)

IX. Complete syntheses.

In addition to the syntheses accomplished by Wallach8) with the aid of ketones and bromaceticester and its homo-logues, the following may here be mentioned: viz., the synthesis of v2,4-menthadiene from succinyl succinic acid by v. Baeyer,9) that of dipentene10) and carvestrene11) by Per-kin jun. and the more recent syntheses of Komppa in the camphor group.12)

1) Wallach, Liebig's Annalen 359 (1908), 283.

2) Auwers and v. d. Heyden, Berl. Berichte 42 (1909), 2404.

3) Bertram and Walbaum, )ourn. f. prakt. Chem. II. 45 (1892), 601.

4) Bertram and Gildemeister, Ibidem II. 49 (1894), 194; Tiemann and Schmidt, Berl. Berichte 28 (1895), 2134.

5) Tiemann and Semmler, Berl. Berichte 28 (1895), 2134.

6) Tilden, Journ. chem. Soc. 45 (1884), 410; Bouchardat, Compt. rend. 80 (1875), 1446; 87 (1878), 654; 89 (1879), 361, 1117.

7) Bouchardat, Bull. Soc. chim. II. 33 (1880), 24.

8) Wallach, Terpene und Campher. Leipzig 1909, p. 145.

9) Berl. Berichte 26 (1893), 232.

10) Journ. chem. Soc. 85 (1904), 654.

11) Ibidem 91 (1907), 480.

12) Liebig's Annalen 368 (1909), 110; 370 (1909), 209.

Santene = Norcamphene.

C Alicyclic Hydrocarbons 112

First of all there may be mentioned a lower homologue of the terpenes, the santene, C9H14, which has been observed repeatedly in recent years. Its occurrence has been observed in East-Indian sandalwood oil, in Siberian pine-needle oil, in the German Fichtennadelol, in the needle oil of the German Abies alba and in the Swedish Fichtennadelol from Picea excelsa. The following constants of this oil have been recorded:

B. p. 31 to 33° (9 mm); d20,0,863; aD + 0°; nD 1,46658.1) B. p. 140°; d15o0,8698; aD±0°; nD19.2o1,46960.2)

Upon hydration with the acetic acid-sulphuric acid mixture according to Bertram, santene is converted into a bicyclic saturated alcohol, the santenol (n-norborneol), b. p. 195 to 196°; m. p. 97 to 98°. When treated with chlorinating agents this yields norbomyl chloride, respectively norisobornyl chloride. By splitting off hydrogen chloride from these chlorides, Semmler3) obtained norcamphene, which is identical with santene.

Characteristic derivatives of santene are its nitrosochloride, m. p. 109 to 110°; its chlorhydrate, m. p. 80 to 81°; its tribromide, m. p. 62 to 63°; and its nitrosite, m. p. 124 to 125°. For its identification Semmler suggests its tribromide. However, according to Aschan's observations, the santenes of different sources yield tri-bromides with varying melting points. Hence Aschan considers the nitrosite as better adapted for the identification of santene. As a further derivative suitable for the identification of santene, a-Pinene is very widely distributed and occurs in the inactive as well as in both optically active forms. Whereas pinene does not often occur in flowers, it is found more frequently in the oils from leaves, barks, and woods. It is the principal constituent of the distillate from the oleoresins of the several species of Pinus, which distillates are known in commerce as turpentine oils. French and Spanish turpentine oils contain as principal constituent /-a-pinene, whereas in American and Greek oils the dextrogyrate modification predominates. However, there are also American oils which are laevogyrate or nearly inactive.

1) Semmler, Berl. Berichte 40 (1907), 4595.

2) Aschan, Bed. Berichte 40 (1907), 4920.

3) Bed. Berichte 41 (1908), 128.

Semmler and Bartelt1) mention the santene glycol (m. p. 197°; b. p. 135° at 10 mm), which is obtained by careful oxidation of the hydrocarbon in acetone solution with potassium permanganate.

C Alicyclic Hydrocarbons 113

The hydrocarbon d-a-p'mene (the australene of Berthelot), besides occurring in American and Greek turpentine oil, has been found in Burmese turpentine oil, in the turpentine oil from Pinus sylvestris, in German, Polish and Swedish pine tar oils, in larch needle oil, in German and Swedish Kiefemade/o1, in Zirbel-kiefernadelol, in the oil from the leaves of Juniperus phoenicea and Callitris glauca, sandarac oil, in oil from the leaves of Sequoia gigantea, in cypress oil, in oil from the leaves and twigs of Thuja plicata, in the oil of Alpinia malaccensis, in the oils of galangal, star anise, ylang-ylang, nutmeg, camphor, apopin, Persea, in the oil from the fruits of Pittosporum undulatum, in Chios turpentine oil, in the oils of myrtle and checken, in the oils of Melaleuca uncinata and M. nodosa, in niaouli oil, in the oils of Leptospermum Liversidgei, Eucalyptus botryoides and E. dextropinea, in ajowan oil, coriander oil, carrot oil, cumin oil, asafetida oil, galbanum oil, fennel oil, water fennel oil (?), rosemary oil and in the basilicum oil from Reunion.

1) Berl. Berichte 41 (1908), 866.

/-a-Pinene (the terebenthene of Berthelot) is contained in French turpentine oil, in the turpentine oil from Picea excelsa, in the Canada balsam oil from Abies balsamea, A. amabilis, in Oregon balsam oil from Pseudotsuga mucronata, in the needle oil from Pinus Strobus, in Eichtennadelol, in the Seestrandkieferknospenol, in the needle oil from Pinus montana, in the English Kiefernadelol, in hemlock needle oil, in the oils from the leaves and cones of Abies alba, in the needle oils from Abies canadensis, Picea nigra, P. alba, Abies balsamea and A. sibirica, in the oil of cubeb (?), the oils of Asarum europaeum and A. arifolium, in the oils of Ceylon cinnamon and Canella alba, in the oil from Umbellularia californ-ica, in the geranium oil from Reunion, in the oils of petitgrain, lemon, neroli, rue, frankincense, dacryodes resin and cajeput, in the oils from Eucalyptus carnea, E. laevopinea and E. Wilkinsoniana, in the oils from parsley, lavender, marjoran, American pennyroyal, spearmint (?), French peppermint, valerian, and kessoroot.