Pure citronellol is a colorless oil with an agreable, rose-like odor, but finer than that of geraniol. According to its method of formation it reveals slight variations in its physical properties. Wallach5) determined the following constants in connection with a citronellol (reuniol) obtained according to his method (see above):
B. p. 114 to 115° (12 to 13 mm.); d22o0,856; aD -1°40'; nD22° 1 ,45609.
According to Tiemann and Schmidt,6) d-citronellol obtained by reduction of citronellal, possesses the following properties:
B. p. 117 to 118° (17 mm.); d17.5 o0,8565; [a]D17(6. + 4°; nD 1,45659.
/-Citronellol, prepared from rose oil by means of the phosphorus trichloride method, boils at 113 to 114° at 15 mm. pressure; d20o 0,8612; nD 1,45789; and deviates polarized light 4°20' to the left.7)
For the alcohol, obtained from Reunion geranium oil according to a method similar to that of Wallach, the following constants are recorded:
B. p. 225 to 226° (764,5 mm.); d16o0,862; aD -1°40'; nD22o 1,45611.8).
1) Dodge, Americ. chem. Journ. 11 (1889), 463; Tiemann and Schmidt, Berl. Berichte 29 (1896), 906; Erdmann, Journ. f. prakt. Chem. II. 56 (1897), 38. 2) Berl. Berichte 31 (1898), 2899. 3) Compt. rend. 138 (1904), 1699.
4) Liebig's Annalen 278 (1894), 316; 296 (1897), 129.
5) Nachr. K. Ges. Wiss. Gottingen 1896, Session of February 8.; Neaschold, Beitrage zur Kenntnis aliphatischer Terpenverbindungen. Inaug.-Dissert. Gottingen 1896. p. 56.
6) Berl. Berichte 29 (1896), 906.
7) Tiemann and Schmidt, Berl. Berichte 29 (1896), 923.
8) Report of Schimmel & Co. April 1898, 58.
In the laboratory of Schimmel& Co. the following constants were observed in connection with their own preparations:
Citronellol from Java citronella oil: B. p. 109° (7 mm.); 103° (5 mm.); d15o.0,8604 to 0,8629; aD + 2°7' to + 2°32'; nD22o1,45651 to 1,45791; m. p. of the silver salt of the acid phthalic acid ester 125 to 126V)
Citronellol from geranium oil: B. p. 225 to 226° (764,5 mm.); d15o0,862 to 0,869; aD slightly kevogyrate to - 1°52'; nD20o 1,459 to 1,463; soluble in about 14 vols. 50 p. c. alcohol and in 3 to 4 vols, of 60 p. c. alcohol.
Citronellol is much more stable than geraniol and is not acted upon when heated with alkali. When shaken with a 10 p. c. sulphuric acid it adds water and is converted into a diatomic alcohol from which dehydrating agents regenerate citronellol.2) Attempts to prepare a cyclic hydrocarbon C10H18 by dehydration have not been successful thus far. Its stability toward phosphorus trichloride in the cold, phthalic acid anhydride and formic acid at higher temperatures, and toward the united action of heat and pressure in the presence of water, has already been referred to in the discussion of the methods by which citronellol can be separated from the other alcohols. It is also worth mentioning that sulphurous acid and sodium acid sulphite can be added to the doubly linked carbon atoms of citronellol.
As a primary alcohol, citronellol first yields the aldehyde citronellal, C10Hl8O, which, upon reduction with sodium amalgam, can be reconverted into the alcohol. As is the case with geraniol, the oxidation to the aldehyde is by no means quantitative, other oxidation products, such as citronellic acid, etc, resulting.3) If citronellol is first hydroxylized with dilute permanganate solution and the resulting glycol oxidized further with chromic acid mixture, acetone and B-methyladipinic acid result. According to the optical character of the citronellol, the latter oxidation product is obtained more or less active, or optically inactive. The melting point also varies accordingly from 82 to 96°. In as much as citronellol can also be converted into the cyclic alcohol iso-pulegol and this into pulegone, it has been assigned the formula dimethyl-2,6-octene-2-ol-8.
1) Report of Schimmel & Co. April 1902, 14.
2) Tiemann and Schmidt, Berl. Berichte 29 (1896), 907.
3) Tiemann and Schmidt, Berl. Berichte 30 (1897), 34.
CH8 • C (CH3): CH • CH2 • CH2 • CH (CH3) CH2 • CH2 OH.1)
Opposed to this view are the observations of Harries and Himmelmann,2) referred to above, also those of Bouveault, viz., that citronellol is a mixture of two isomeric alcohols; to one of which may be assigned the above formula and to the other the formula
CH3 • C(: CH,) • CH2 • CH2 • CH2 • CH (CH3)CH2CH2OH.
The esters of citronellol, of which the acetate occurs in volatile oils, are readily obtained by the action of the corresponding acid anhydrides on the alcohol. For further statements see under esters.
The acid phthalic acid ester, which results when citronellol and phthalic acid anhydride are heated together, differs from that of geraniol in being liquid. However, it yields a well crystallizable silver salt from which pure citronellol can be regenerated.3)
Citronellol can be characterized by its oxidation to citronellal (which see) and this in turn by means of its citronellyl-B-naphtho-cinchoninic acid, or by means of its semicarbazone4) which melts at 84°. In the absence of geraniol, citronellol can be identified by means of the silver salt of citronellyl phthalic acid which melts at 125 to 126°. Its identification by means of the citronellyl-pyrouvic acid ester, the semicarbazone of which melts at 110 to 111°, can be carried out in the presence of geraniol. For the quantitative determination of citronellol in the presence of other alcohols, its stability toward concentrated formic acid is resorted to. Whereas the other alcohols are destroyed, citronellol, under certain conditions, is converted into the formate. For further details see the chapter "The examination of volatile oils".
1) Tiemann and Schmidt, Berl. Berichte 29 (1896), 908.
2) Berl. Berichte 41 (1908), 2187.
3) Erdmann and Huth, Journ. f. prakt. Chem. II. 56 (1897), 41.
4) Tiemann and Schmidt, Berl. Berichte 30 (1897), 34; 31 (1898), 3307. However, other semicarbazones with different melting points are known. See under citronellal.
Of other alcohols, found in volatile oils, that are regarded as aliphatic compounds, the following should be mentioned:
Andro/1) is the name assigned to an alcohol of like composition with citronellol, which appears to impart to water fennel (Phellandrium aquaticum) its characteristic odor. It may be recognized by its physical constants (b. p. 197 to 198°; d15o 0,858; aD - 7° 10'; nD20o 1,44991) and by its phenylurethane which melts at 42*to 43°. Nothing further is known about its constitution.
Unclneol, C10H18O, is the name given by Baker and Smith2) to an alcohol which they found in that portion of cajeput oil (Malaleuca uncinata) which boils above 197°. When pure, this alcohol consists of snowwhite crystalline needles which melt at 72,5°; [a]D + 36,99° in alcoholic solution.
An alcohol with a rose-like odor has also been found in fraction 230° of waterfennel oil.3) Its phenylurethane melts between 87 to 90°. In patchouli oil4) there likewise has been found an alcohol with a rose-like odor. However, nothing further has as yet been recorded.