Geraniol is amonoterpenoid and analcohol. It is the primary component ofcitronella oil and is a primary component ofrose oil andpalmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in water, but it is soluble in common organic solvents.
Geraniol is produced by thescent glands ofhoneybees to mark nectar-bearing flowers and locate the entrances to their hives.[6] It is also commonly used as an insect repellent, especially for mosquitoes.[7]
The scent of geraniol is reminiscent of, but chemically unrelated to, 2-ethoxy-3,5-hexadiene, also known asgeranium taint, a wine fault resulting from fermentation ofsorbic acid bylactic acid bacteria.[8]
Inacidic solutions, geraniol is converted to the cyclic terpeneα-terpineol. The alcohol group undergoes expected reactions. It can be converted to thetosylate, which is a precursor to the chloride. Geranyl chloride also arises by theAppel reaction by treating geraniol with triphenylphosphine and carbon tetrachloride.[11][12] It can be oxidized to the aldehydegeranial.[13] Hydrogenation of the two C=C bonds over a nickel catalyst gives tetrahydrogeraniol.[14][15]
Geraniol was first isolated in pure form in 1871 by the German chemistOscar Jacobsen (1840–1889).[17][18] Usingdistillation, Jacobsen obtained geraniol from an essential oil produced in India which was obtained from the so-calledgeranium grass.[19] This essence, after which the compound was named, was a 50% cheaper substitute for the essence of the propergeranium flower with a similar, although less delicate, odor.[20]
The chemical structure of geraniol was determined in 1919 by the French chemistAlbert Verley (1867–1959).[21]
^Jacobsen, Oscar (1871)."Untersuchung der indischen Geraniumöls" [InvestIgation of Indian oil from geranium [grass]].Annalen der Chemie und Pharmacie (in German).157:232–239. Jacobsen named geraniol on p. 234:"Danach ist dieser Körper, das Geraniol, isomer mit dem Borneol … " (Accordingly this body [i.e., substance], geraniol, is isomeric with borneol … )
^Semmler, F.W. (1906).Die ätherischen Öle [The Volatile Oils] (in German). Vol. 1. Leipzig, Germany: Von Veit & Co. p. 292. From p. 292:"Von dem Geraniol ist zu erwähnen, daß … erst Jacobsen (A.157, 232) brachte im Jahre 1870 über den Alkohol, den er Geraniol nannte, nähere Angaben, er stellte die Formel C10H18O auf, ohne weitere Konstitionsangaben zu machen." (It should be mentioned about geraniol that … Jacobsen (A.157, 232) first gathered in 1870 more detailed data about the alcohol, which he named geraniol ; he established its [empirical] formula C10H18O, without providing further data about its chemical structure.) See also: §49. Geraniol C10H18O, pp. 439-493. On p. 439, two hypothetical structures of geraniol are proposed.
^Verley, Albert (1919)."Sur la constitution du géraniol, du linalool et du nérol" [On the chemical structure of geraniol, linalool, and nerol].Bulletin de la Société Chimique de France. 4th series (in French).25:68–80. The chemical structure of geraniol appears on p. 70.
