Eucalyptol (also called cineole) is a monoterpenoid colorless liquid, and a

bicyclic A bicyclic molecule () is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (all of the ring ...

ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R� ...

. It has a fresh

camphor Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (''Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapu ...

-like odor and a spicy, cooling taste. It is insoluble in water, but

miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). Such substances are said to be miscible (etymologically ...

with organic solvents. Eucalyptol makes up about 70–90% of

eucalyptus oil Eucalyptus oil is the generic name for distilled oil from the leaves of ''Eucalyptus'', a genus of the plant family Myrtaceae, mostly native to Australia but cultivated worldwide. Eucalyptus oil has a history of wide application, as a pharmace ...

. Eucalyptol forms crystalline

adduct In chemistry, an adduct (; alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is ...

s with hydrohalic acids, ''o''-cresol,

resorcinol Resorcinol (or resorcin) is a phenolic compound. It is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or ''meta- (chemistry), meta''-isomer). Resorcinol crystallizes from benzene as co ...

, and

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, ...

. Formation of these adducts is useful for purification. In 1870, F. S. Cloez identified and ascribed the name "eucalyptol" to the dominant portion of ''

Eucalyptus globulus ''Eucalyptus globulus'', commonly known as southern blue gum or blue gum, is a species of flowering plant in the family Myrtaceae. It is a tall, evergreen tree Endemism, endemic to southeastern Australia. This ''Eucalyptus'' species has most ...

'' oil.

Uses

Because of its pleasant, spicy aroma and taste, eucalyptol is used in flavorings, fragrances, and cosmetics. Cineole-based eucalyptus oil is used as a flavoring at low levels (0.002%) in various products, including

baked goods Baking is a method of preparing food that uses dry heat, typically in an oven, but it can also be done in hot ashes, or on hot Baking stone, stones. Bread is the most commonly baked item, but many other types of food can also be baked. Heat is ...

confectionery Confectionery is the Art (skill), art of making confections, or sweet foods. Confections are items that are rich in sugar and carbohydrates, although exact definitions are difficult. In general, however, confections are divided into two bro ...

meat Meat is animal Tissue (biology), tissue, often muscle, that is eaten as food. Humans have hunted and farmed other animals for meat since prehistory. The Neolithic Revolution allowed the domestication of vertebrates, including chickens, sheep, ...

products, and

beverages A drink or beverage is a liquid intended for human consumption. In addition to their basic function of satisfying thirst, drinks play important roles in human culture. Common types of drinks include plain drinking water, milk, juice, smoothie ...

. In a 1994 report released by five top cigarette companies, eucalyptol was listed as one of the 599 additives to cigarettes. It is claimed to be added to improve the flavor. Eucalyptol is an ingredient in commercial

mouthwash Mouthwash, mouth rinse, oral rinse, or mouth bath is a liquid which is held in the mouth passively or swirled around the mouth by contraction of the perioral muscles and/or movement of the head, and may be gargled, where the head is tilted back ...

es.

Other

Eucalyptol exhibits

insecticidal Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, in ...

and

insect repellent An insect repellent (also commonly called "bug spray" or "bug deterrent") is a substance applied to the skin, clothing, or other surfaces to discourage insects (and arthropods in general) from landing or climbing on that surface. Insect repellent ...

properties. In contrast, eucalyptol is one of many compounds that are attractive to males of various species of orchid bees, which gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study. One such study with ''

Euglossa imperialis ''Euglossa imperialis'' is a bee species in the family Apidae. It is considered to be one of the most important pollinators to many Neotropical orchid species in mainland tropical America. It is also one of the most common non-parasitic Euglossin ...

'', a nonsocial orchid bee species, has shown that the presence of cineole (also eucalyptol) elevates territorial behavior and specifically attracts the male bees. It was even observed that these males would periodically leave their territories to forage for chemicals such as cineole, thought to be important for attracting and mating with females, to synthesize pheromones.

Toxicology

Eucalyptol has a toxicity ( LD₅₀) of 2.48 grams per kg (rat). Ingestion in significant quantities is likely to cause headache and gastric distress, such as nausea and vomiting. Because of its low

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

, it may directly enter the lungs if swallowed, or if subsequently vomited. Once in the lungs, it is difficult to remove and can cause

delirium Delirium (formerly acute confusional state, an ambiguous term that is now discouraged) is a specific state of acute confusion attributable to the direct physiological consequence of a medical condition, effects of a psychoactive substance, or ...

, convulsions, severe injury or death. Consequently, eucalyptol should never be ingested unless in highly diluted formulations. Toxicity is significantly reduced when administered topically. However it should not be used topically during pregnancy, breastfeeding, or on children under two.

Biosynthesis

Eucalyptol is generated from

geranyl pyrophosphate Geranyl pyrophosphate (GPP), also known as geranyl diphosphate (GDP), is the pyrophosphate ester of the terpenoid geraniol. Its salts are colorless. It is a precursor to many thousands of natural product, natural products. Occurrence GPP is an int ...

(GPP) which isomerizes to (''S'')-linalyl diphosphate (LPP). Ionization of the pyrophosphate, catalyzed by cineole synthase, produces eucalyptol. The process involves the intermediacy of alpha-terpinyl cation. Eucalyptol synthesis

Plants containing eucalyptol

* ''

Aframomum corrorima ''Aframomum corrorima'' is a species of flowering plant in the ginger family, Zingiberaceae. It is an herbaceous perennial that produces leafy stems 1–2 meters tall from rhizomatous roots. The alternately-arranged leaves are dark green, 10–3 ...

'' * ''

Artemisia tridentata '' Artemisia tridentata'', commonly called big sagebrush,MacKay, Pam (2013), ''Mojave Desert Wildflowers'', 2nd ed., , p. 264. Great Basin sagebrush or simply sagebrush (one of several related species of this name), is an aromatic shrub from the ...

'' * ''

Cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...

'' * ''

Cinnamomum camphora ''Camphora officinarum'' is a species of evergreen tree indigenous to warm temperate to subtropical regions of East Asia, including countries such as China, Taiwan, Vietnam, Korea, and Japan. It is known by various names, most notably the camph ...

'', camphor laurel (50%) * ''

'' * ''

Eucalyptus largiflorens ''Eucalyptus largiflorens'', or black box or river box, is a tree that is endemic to Australia. It has rough, fibrous or flaky bark, dull greenish-grey, lance-shaped leaves, oval to club-shaped green to yellow flower buds, white flowers and hemi ...

'' * '' Eucalyptus salmonophloia * '' Eucalyptus staigeriana'' * '' Eucalyptus wandoo'' * '' Hedychium coronarium'', butterfly lily * '' Helichrysum gymnocephalum'' * ''

Kaempferia galanga ''Kaempferia galanga'', commonly known as kencur, aromatic ginger, sand ginger, cutcherry, is a monocotyledonous plant in the ginger family, and one of four plants called galangal. It is found primarily in open areas in Indonesia, southern C ...

'', galangal, (5.7%) * ''S. officinalis'' subsp. ''lavandulifolia'' (syn. ''S. lavandulifolia''), Spanish sage (13%) * '' Salvia rosmarinus, rosemary * '' Turnera diffusa'', damiana * '' Umbellularia californica'', pepperwood (22.0%) * '' Zingiber officinale'', ginger

References

{{Transient receptor potential channel modulators Cooling flavors Monoterpenes Ethers Tree-derived bioactive compounds

Uses

Other

Toxicology

Biosynthesis

Plants containing eucalyptol

See also

References