Isomeric with linalool is geraniol C10H18O which is distinguished from the former by its optical inactivity, higher boiling point and higher specific gravity. It is the "lemonol" of Barbier and Bouveault, the "rhodinol" of Erdmann and Huth and of Poleck. Both as such and as ester it is found rather frequently in volatile oils. It constitutes the bulk of palmarosa oil, of German and Turkish rose oils, and is found in appreciable quantities in the oils of geranium, citronella and lemongrass. It has further been found in the oils of gingergrass, Canada snakeroot, ylang-ylang, champaca flowers, nutmeg, sassafras leaves, laurel leaves, kuro-moji, tetranthera (?), cassie flowers (from Acacia Cavenia and A. Fames/ana), neroli, petitgrain, coriander, Mexican and Cayenne lignaloe, of Darwinia fascicularis (?), Eucalyptus Macarthuri, E. Staigeriana, Leptospermum Liversidgei, verbena, spike (?) and lavender. As acetate it occurs in the needle oil of Callitris glauca, the oils of palmarosa, lemongrass, sassafras leaves, kuro-moji, lemon, petitgrain, Eucalyptus Macarthuri, E. Staigeriana, Leptospermum Liversidgei, Darwinia fascicularis and lavender; as Isovalerianate in sassafras leaf oil; as /7-capronate in pal-marosa and lavender oils; and as tiglinate in geranium oil.
1) Semmler, Berl. Berichte 27 (1894), 2520.
2) Berl. Berichte 41 (1908), 2083; Recueil des trav. chim. des P.-B. 27 (1908), 411; Chem. Zentralbl. 1908, II. 1926.
As a primary alcohol, geraniol forms a crystalline addition product with calcium chloride,1) which is insoluble in ether, ligroin, benzene and chloroform, and which is resolved into its components by water. By this extremely simple method, geraniol can be obtained chemically pure (see below). With magnesium chloride, calcium nitrate and magnesium nitrate, crystalline derivatives are likewise formed.2)
For the isolation of geraniol from mixtures with hydrocarbons and other substances a number of other methods have been suggested. All of them have this in common that they aim at the preparation of an acid phthalate of geraniol. This ester can be prepared either by the action of phthalic acid anhydride on the sodium compound of crude geraniol,3) or by heating geraniol with phthalic acid anhydride without solvent in the water bath4) or in benzene solution.5) The ester can be purified through the crystalline silver salt. The geraniol is regenerated by saponifying either the acid ester, or its sodium salt, the latter being prepared from the silver salt. These methods, however, do not possess any advantages over the calcium chloride method. Indeed, they are more complicated and yield no purer product.
1) Jacobsen, Liebig's Annalen 157 (1871), 234.
2) Report of Schimmel & Co. April 1895, 44.
3) Tiemann and Kruger, Bed. Berichte 29 (1896), 901.
4) H. and E. Erdmann, Journ. f. prakt. Chem. II. 56 (1897), 15.
5) Flatau and Labbe, Compt. rend. 126 (1898), 1725; Bull. Soc. chim. III. 19 (1898), 633; Stephan, Journ. f. prakt. Chem. II. 60 (1899), 248.
Purified geraniol, prepared by one or the other of the above mentioned methods, is a colorless, oily liquid with a rose-like odor which is optically inactive. When exposed to the air it is modified, taking up oxygen and suffering in its fragrance. Its properties are recorded as follows:
B. p. 110 to 111° (10 mm.), 121° (18 mm.), 230° (under atmospheric pressure).1)
B. p. 120,5 to 122,5° (17 mm.); d20o0,8894 (!); nD20o 1,4766.2) B. p. 110,5 to 111° (corn, at 10 mm.); d 16o/4o0,8812.3) d15o 0,880 to 0,883; nD17o 1,4766 to 1,4786.*)
In connection with products prepared by themselves on a large scale Schimmel & Co. observed the following properties:
B. p. 229 to 230° (757 mm.), 114 to 115° (12 mm.); d15o 0,883 to 0,886; nD20o 1,476 to 1,478; soluble in 8 to 15 vols, of 50 p. c. alcohol and in 2,5 to 3,5 vols, of 60 p. c. alcohol.
Upon oxidation geraniol, as primary alcohol, yields citral, from which it can again be obtained by reduction.5) In as much as citral has been obtained synthetically, geraniol also belongs to those substances that can thus be obtained.
Upon application of Sabatier and Senderens'6) method, Bouveault7) succeeded in converting geraniol well nigh quantitatively into citral. This method consists in the catalytic action of copper on primary alcohols at high temperature.
Geraniol, or rather its acetate, results together with terpineol and nerol, when linalool is heated for a long time with acetic acid anhydride.1) The reverse reaction takes place when geraniol is heated with water to 200° in an autoclave. At higher temperatures hydrocarbons and their polymerization products are formed.2) When hydrogen chloride is allowed to act on a mixture of geraniol and toluene, linalyl chloride results which, with silver nitrate, yields linalool.3) Hence it can be explained how Tiemann3) could obtain linalool when treating geraniol with hydrogen chloride and saponifying the reaction product with alcoholic potassa.
1) Bertram and Gildemeister, Journ. f. prakt. Chem. II. 56 (1897), 508.
2) Tiemann and Semmler, Berl. Berichte 36 (1893), 2711.
3) H. and E. Erdmann, Journ. f. prakt. Chem. II. 56 (1897), 3; Berl. Berichte 31 (1898), 359, Anm. 1.
4) Stephan, Journ. f. prakt. Chem. II. 58 (1898), 110; 60 (1899), 244. 5) Tiemann, Berl. Berichte 31 (1898), 828.
6) Compt. rend. 136 (1903), 738, 921, 983. 7) Bull. Soc. chim. IV. 3 (1908), 119.
In general, geraniol is not as readily acted upon by acids as is linalool. However, the action of acid reagents may cause ring formation, cyclogeraniol being produced. When boiled with acetic acid anhydride it is quantitatively converted into the acetate, but not isomerized. When shaken with dilute sulphuric acid it is converted into terpinhydrate, as is linalool, but not as readily.4) Concentrated formic acid, like potassium acid sulphate or phosphoric acid, acts as dehydrating agent. Whereas the action of potassium acid sulphate is said to produce an open chain hydrocarbon,5) the other reagents produce terpenes. Thus formic acid produces a-terpineol, dipentene and terpinene.6). Upon reduction of geraniol with platinum sponge and hydrogen, Willstatter and Mayer7) obtained a mixture of 2,6-dimethyl octane and 2,6-di-methyloctanol-8. The same products were obtained by Enklaar8) with Sabatier's method. In addition, however, there resulted a cyclic alcohol C10H20O not further characterized.