In the presence of water and oxygen, pinene yields pinol hydrate (sobrerol) C10H18O2, which is at times found in old turpentine oils as a crystalline deposit. The active modifications of pinol hydrate melt at 150°, the inactive modification at 130,5 to 131°. When boiled with acids, pinol hydrate yields the oxide pinol, C10H16O, with its characteristic odor. In contact with dilute mineral acids, pinene is converted into terpin hydrate, C10H18(OH)2, H20 (m. p. 116 to 117°). As an intermediate product terpineol is formed, which likewise results upon the hydration of pinene with sulphuric and acetic acids.

When shaken with a 3 to 5percent, sulphuric acid, pinene is acted upon but slowly.1) A suitable method for the hydration of pinene, according to Barbier and Grignard,'2) consists in acting on a solution of pinene in glacial acetic acid and acetic acid anhydride with a 50 percent, aqueous solution of benzene mono-sulphonic acid.

Oxidizing agents act on pinene in various ways. Whereas concentrated nitric acid produces so violent a reaction that ignition may take place, dilute nitric acid, like chromic acid mixture, produces - with pinol hydrate or pinol as intermediate products - in addition to lower fatty acids and other products, tere-phthalic acid, C8H604, terebic acid, C7H10O4, and terpenylic acid, C8H1204. Essentially different results are obtained with potassium permanganate. As shown by Wagner,3) dilute permanganate solution produces principally neutral oxidation products. When concentrated permanganate is used there results, in addition to other products, pinonic acid,1) C10H16O3, a mono-basic keto acid. Upon further oxidation this yields not only terebic acid, but also the "Abbau" products that are obtained upon oxidation of camphor derivatives.

1) Wallach, Nachr. K. Ges.Wiss. Gottingenl908. Meeting of February 8. p.20.

2) Compt. rend. 145 (1907), 1425; Bull. Soc. chim. IV. 8 (1908), 139; 5 (1909), 512, 519.

3) Bed. Berichte 27 (1894), 2270; 29 (1896), 881.

According to the optical character of the initial material, a pinonic acid results that is optically active ([a]D in chloroformic solution + or - 88 to 90°) respectively inactive. The inactive modification melts at 103 to 105°, its oxime at 150°; of the active modification the acids melt at 69,5 to 70,5°, the oximes at 129° and the semicarbazones at 203 to 204°. Upon inversion with sulphuric acid methoethylheptanonolid results, the active modification of which melts at 46 to 47°, the inactive modification at 63 to 64°.

These compounds are suitable for the characterization of the several modifications of a-pinene. When pinene is acted upon by ozone, ozonides result which, upon cleavage with water, yield pinonic acid.2) a-Pinene is an unsaturated hydrocarbon with one double bond. Upon addition it is readily converted into derivatives of camphor. When dry hydrogen chloride or hydrogen bromide are passed into well dried and cooled pinene, halogenides of borneol result. Of these the chloride (the socalled "pinene chlor-hydrate"), C10H16HC1, was designated "artificial camphor" because of its camphor-like odor. It melts at 125 to 127°; the bromide, C10H16HBr, melts 90°. Both yield camphene when hydrohalogen is split off. True pinene monochlorhydrate was obtained by Wallach by the action of phosphorus pentachloride upon homonopinol. If bromine is allowed to act on pinene in dry solution, one molecule of bromine is readily decolorized and added. More bromine is added but slowly and is accompanied by the development of hydrogen bromide. When the addition product of one molecule of bromine to pinene is distilled with steam a dibromide melting at 169 to 170° is obtained.3) A better yield, however, is obtained by allowing hypobromous acid to act on pinene. This dibromide also appears to be a camphor derivative.1) When this dibromide is acted upon with aniline, hydrogen bromide is split off and cymene results. However, when acted upon with zinc dust in alcoholic solution, a new terpene, the tricyclene, m. p. 65 to 66° results.2)

1) Tiemann and Semmler, Berl. Berichte 28 (1895), 1345; 29 (1896); 529, 3027; Baeyer, Berl. Berichte 29(1896), 22, 326, 1907, 1923,2775; Gildemeister and Kdhler, Wallach-Festschrift. Gottingen 1909. p. 426.

2) Harries and Neresheimer, Berl. Berichte 41 (1908), 38.

3) Wallach, Liebig's Annalen 264 (1891), 8.

The presence of -apinene in a volatile oil can be ascertained by means of its nitrosochloride and its oxidation products. Provided the pinene reveals no high optical rotation, it is most readily identified by means of the nitrosochloride and by the conversion of the latter into its nitrolamine bases. For the preparation of the nitrosochloride, Wallach3) has given the following directions: A mixture of 50 g. each of turpentine oil (immaterial whether laevo- or dextrogyrate), glacial acetic acid and ethyl nitrite4) (preferably amyl nitrite)5) is well cooled in a freezing mixture and 15 cc. of crude (33 percent.) hydrochloric acid are gradually added. The nitrosochloride soon separates in a crystalline form, and is obtained in a fairly pure state when it is filtered off with a suction pump and well washed with alcohol. From the filtrate some more nitrosochloride separates on standing in the cold. It is profitable in regard to yield to work with small quantities, as only then can the low temperature be maintained which is necessary for the satisfactory conduct of the reaction; large quantities of pinol C10H16O are formed as a by-product.

The nitrosochloride is a white crystalline powder, which is readily soluble in chloroform and may be again separated from this solution by methyl alcohol. The melting point of the re-crystallized compound is 103°, though melting points as high as 115° have been observed. Like its derivatives it is optically inactive. According to observations by Baeyer6) pinene nitroso-chloride is a bisnitroso compound (C10H16Cl)2N2O2, which in ethereal solution is changed by hydrochloric acid into hydro-chlorocarvoxime.1) By splitting off hydrochloric acid with alcoholic potassa it is converted into nitrosopinene (m. p. 132°)2) which has been recognized as an oxime.3) Aromatic bases, such as aniline and toluidine split off nitrosylchloride, regenerating pinene with the formation of amidoazo-compounds. Quite different is the behavior of the nitrosochloride toward bases of the fatty series and those which possess their characteristics, as for instance, benzylamine and piperidine. With primary bases as well as with piperidine, nitrolamines result; the secondary bases, like diethyl-amine, however, produce a splitting-off of hydrochloric acid with the resulting formation of nitrosopinene.

1) Wagner and Ginzberg, Bed. Berichte 29 (1896), 890.

2) Godlewsky and Wagner, Chem. Ztg. 21 (1897), 98.

3) Liebig's Annalen 245 (1888), 251; 253 (1889), 251.

4) This is easily obtained by allowing a mixture of 200 g. of concentrated sulphuric acid, 1,5 liters of water and 100 g. of alcohol to flow into a solution of 250 g. of sodium nitrite in 1 liter of water and 100 g. of alcohol. The ethyl nitrite which forms at once must be condensed in well cooled receivers.

5) Report of Schimmel & Co. November 1908, 63. 6l) Berl. Berichte 28 (1895), 648.