Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil and palmarosa 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. The functional group derived from geraniol (in essence, geraniol lacking the terminal −OH) is called geranyl.

Uses and occurrence

In addition to being found in rose oil, palmarosa oil, and citronella oil, it also occurs in small quantities in geranium, lemon, and many other essential oils. With a rose-like scent, it is commonly used in perfumes and in scents such as peach, raspberry, grapefruit, red apple, plum, lime, orange, lemon, watermelon, pineapple, and blueberry. Geraniol is produced by the scent glands of honeybees to mark nectar-bearing flowers and locate the entrances to their hives. It is also commonly used as an insect repellent, especially for mosquitoes. The scent of geraniol is reminiscent of, but chemically unrelated to, 2-ethoxy-3,5-hexadiene, also known as geranium taint, a wine fault resulting from fermentation of sorbic acid by lactic acid bacteria. Geranyl pyrophosphate is important in biosynthesis of other terpenes such as myrcene and ocimene. It is also used in the biosynthesis pathway of many cannabinoids in the form of CBGA.

Reactions

In acidic solutions, geraniol is converted to the cyclic terpene α-terpineol. The alcohol group undergoes expected reactions. It can be converted to the tosylate, which is a precursor to the chloride. Geranyl chloride also arises by the Appel reaction by treating geraniol with triphenylphosphine and carbon tetrachloride. It can be oxidized to the aldehyde geranial. Hydrogenation of the two C=C bonds over a nickel catalyst gives tetrahydrogeraniol.

Health and safety

Geraniol is classified as D2B (Toxic materials causing other effects) using the Workplace Hazardous Materials Information System (WHMIS).

History

Geraniol was first isolated in pure form in 1871 by the German chemist Oscar Jacobsen (1840–1889). Using distillation, Jacobsen obtained geraniol from an essential oil which was obtained from geranium grass (Andropogon schoenanthus) and which was produced in India. The chemical structure of geraniol was determined in 1919 by the French chemist Albert Verley (1867–1959).