Linalool 127

Linalool, the "licareol" of Barbier, which is more or less widely distributed and which occurs in both optical modifications, constitutes the bulk of lignaloe oil. The Mexican lignaloe oils contain both d- and /-linalool: the dextrogyrate alcohol in the oil of the seeds, the lasvogyrate in the oil of the wood. In the Cayenne lignaloe oil /-linalool only has been found. d-Linalool has also been found in the oil of Canada snake root, and the oils of nutmeg, wartara, sweet orange, and coriander; /-linalool in ylang-ylang oil, the oils of champaca flowers, Ceylon cinnamon, of the leaves of Cinnamomum Loureirii, laurel leaves, sassafras leaves, rose, Reunion geranium, bergamot, neroli, petit-grain, lemon, Italian limetta, spike, thyme, Spanish hops, Musca-telle sage, German and French basilicum, and Russian spearmint. In the following oils linalool has been found, but no record has been made of the direction of optical rotation, viz., in the oils of citronella, hops, kuromoji, limetta leaves, the bark of Cinnamomum pedunculatum, the root of C Loureirii, mandarin, and gardenia. As acetate, linalool has been found in the oil of sassafras leaves, the oil of the root of Cinnamomum pedun-culatum, the oils of bergamot, petitgrain, lemon, neroli, Italian limette, in jasmin flower oil, in lavender oil, in Muscatelle sage oil, in the leaf oil of Mentha citrata and in gardenia oil. As butyrate, linalool has been found in lavender oil, as isobutyrate in Ceylon cinnamon oil and as isovalerate in sassafras leaf oil. An ester of linalool also occurs in oil of hops.

The isolation of pure linalool from a crystalline derivative has not yet succeeded. Hence it is necessary to obtain it by fractionation of the oil which has previously been saponified. As a result, the constants recorded for linalool apply to products thus obtained. If it is desired to free the alcohol from indifferent substances, such as the terpenes, it can be converted into the sodium salt of the acid phthalic ester according to Tiemann's method1) by allowing phthalic acid anhydride to act on sodium linalool. The sodium salt of this acid phthalic ester of linalool is soluble in water and can be saponified with alcoholic potassa. In as much as linalool is subject to changes when distilled from an alkaline solution with water vapor2) -changes that are indicated by a reduction in the optical rotation - the regenerated alcohol must be shaken out of the alcoholic-alkaline solution by means of ether.

According to the nature of the crude material, also according to the method of preparation, products have been obtained that varied slightly in their properties. In judging the purity of a product the following data may be used for comparison.

B. p. 197 to 199°, 85 to 87° (10 mm.); d15o0,870 to 0,875; nD20o 1,4630 to 1,4690.3)

B. p. 86 to 87° (14 mm.); d20o 0,8622 (?); nD 1,46108.4)

B. p. 198 to 199° (760 mm.), 88,3 to 89,5° (13 mm.); d15o0,870; nD20Ol,4668.5)

In connection with technical products obtained in the laboratory of Schimmel & Co., the following constants have been observed:

B. p. 197 to 199°, 69 to 71° (4 mm.); d15o0,869 to 0,873; aD - 3° to -17°, resp. +9° to +13°; nD20o1,462 to 1,464; soluble in 10 to 15 vols. of 50 p. c. alcohol, in 4 to 5 vols, of 60 p. c. and 1 to 2 vols, of 70 p. c. alcohol.

The angle of rotation is not fixed, the highest thus far observed is that for /-linalool from limette oil [a]D - 20° 7',3) for tf-linalool from sweet orange oil [a]D+ 19° 18'.1) In most instances, and more particularly in specimens with a low angle of rotation, the products are, no doubt, mixtures of both optical modifications, in which one or the other predominates.

1) Berl. Berichte 31 (1898), 837.

2) These changes appear to be of a chemical nature and not due merely to inversion. The angle of rotation of /-linalool is not altered by boiling with potassium hydroxide. Charabot, Bull. Soc. chim. III. 21 (1899), 549.

3) Stephan, Journ. f. prakt. Chem. II. 58 (1898), 110.

4) Tiemann, Berl. Berichte 31 (1898), 834.

5) Gildemeister, Arch, der Pharm. 233 (1895), 179.

Artificially linalool can be obtained, though in the inactive modification only, when geraniol is heated with water to 200° in an autoclave;2) or by the action of hydrogen chloride on geraniol and subsequent treatment of the linalyl chloride thus obtained with alcoholic potassa or silver nitrate.3) As to its formation from geranylphthalate of sodium see p. 361.

As an unsaturated alcohol with two double bonds, linalool reveals additive capacity. It combines with bromine, also with hydrohalogen to compounds which, with the exception of linalyl chloride,4) C10H17C1 (b. p. 95 to 96° at 6 mm.), have been investigated but little.

The unsaturated tertiary character of the alcohol is revealed by its behaviour towards reagents. Whereas alkalies act on it but little in the cold, organic acids convert it either into geraniol, nerol, or - in the presence of a little sulphuric acid - into terpineol. Mineral acids change it to cyclic compounds, the change being accompanied either by the abstraction of water or the addition of water. Thus, when shaken with a 5 p. c. sulphuric acid, terpin hydrate is formed;5) when heated with glacial acetic acid and acetic anhydride, there are formed geranyl acetate, the acetate of the solid terpineol6) with an optical rotation opposite to that of the linalool used as starting point, also neryl-acetate.7) Formic acid at room temperature (20°) converts it into its own formate, also into the formate of the solid terpineol with opposite rotation. However, when gently heated (60 to 70°) formic acid dehydrates it, yielding the hydrocarbons dipentene and terpinene.8)

1) Stephan, Journ. f. prakt. Chem. II. 62 (1900), 529.

2) Report of Schimmel & Co. April 189S, 27.

3) Tiemann, Berl. Berichte 31 (1898), 832; Berichte von Roure-Bertrand Fils October 1909, 27.

4) Dupont and Labaune, Berichte von Roure-Bertrand Fils October 1909, 21.

5) Tiemann and Schmidt, Berl. Berichte 28 (1895), 2137. 6) Stephan, Journ. f. prakt. Chem. II. 58 (1898), 109.

7) Zeitschel, Berl. Berichte 39 (1906), 1780.

8) Bertram and Walbaum, Journ. f. prakt. Chem. II. 45 (1892), 601.

Oxidizing agents produce varying results when allowed to act on linalool. With very dilute permanganate solution polyatomic alcohols appear to be formed at first which cannot be isolated in a pure form. Upon further oxidation with permanganate or chromic acid mixture, they yield acetone and Isevulinic acid.1) In accordance with these results, and taking into consideration that linalool is optically active and hence must contain an assym-metric carbon atom, the following formula has been derived,2) namely dimethyl-2,6-octadiene-2,7-ol-6 derivative, or is treated with metallic sodium in alcoholic solution, or when it is heated to 220 to 230° with zinc dust.1) The sodium derivative of linalool is readily soluble in an excess of linalool and can be utilized for preparing this alcohol in a pure state. When reducing linalool with nickel and hydrogen, Enklaar2) obtained, in addition to 2,6-dimethyloctane, 2,6-dimethyloctanol-6,

CH3 • C(CH3): CH • CH2 • CH2 • C(CH3)(OH) • CH : CH2

Possibly, however, the formula given on p. 352 should be assigned to it. If linalool is oxidized with chromic acid mixture only, it first suffers a rearrangement due to the acid character of the oxydizing agent, and is then oxidized to citral, the aldehyde of geraniol.3) As a rule the oxidation is carried farther yielding "Abbau" products of citral, viz., methyl heptenone, lsevulinic acid, etc. The crystal-lyzed oxidation product with hydrogen peroxide, observed by Bertram and Walbaum,3) has revealed itself as terpin hydrate, the formation of which is, in all probability, largely due to mineral acid present in the hydrogen peroxide used.

When heated with sulphur to 160°, linalool and linalyl acetate yield sulphur-containing compounds which Erdmann4) has named "thiozonides". The monothiozonide of linalylacetate, which appears to possess the composition expressed by the formula C12H20O2S3, is a blackish-brown syrup of a peculiar odor. In suitable solvents it produces precipitates with the salts and sulphides of the heavy metals. Of these the gold compound is especially characteristic. Linalool appears to react with both double bonds forming a dithio-zonide, which, however, could not be isolated, since hydrogen sulphide was given off and the compound C10H16OS5 was formed.5)

When acted upon with reducing agents, linalool does not add hydrogen, but readily loses its oxygen with the formation of a doubly unsaturated hydrocarbon linaloolene C10H18. This hydrocarbon results when linalool is converted into its sodium

1) Tiemann and Semmler, Berl. Berichte 28 (1895), 2130.

2) Ibidem 2131.

3) Journ. f. prakt. Chem. II. 45 (1892), 599.

4) Liebig's Annalen 362 (1908), 137.

5) H. Erdmann, loc. cit.

CH3 • CH (CH8) ■ (CH2)3 • C (OH) (CH3) • CH2 • CH3, thus supporting the correctness of the formula of Tiemann and Semmler given above.

The esters of linalool, so far as those occurring in volatile oils are concerned, are liquids with a more or less strong and agreable odor, which cannot be distilled without decomposition under ordinary pressure. The synthetic preparation of these esters, however, is coupled with difficulties since linalool is rather susceptible toward acids. Hence, when linalool is boiled with acid anhydrides or when treated in accordance with the G.I. P. 80711, the products which result consist in the main of esters of linalool, but also contain those of geraniol and terpineol.

Compounds suited to the identification of linalool are the phenylurethane, melting at 65 to 66°, and the a-naphthylurethane melting at 53°. For its further identification it can be oxidized to citral and this characterized by the citral-B-naphthocinchoninic acid discovered by Doebner. If citronellal be present with citral, both are first separated by means of their acid sulphite addition products.