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. It has a fresh camphor-like odor and a spicy, cooling taste. It is insoluble in water, but miscible with organic solvents. Eucalyptol makes up about 70–90% of eucalyptus oil. 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 mouthwashes.

Other

Eucalyptol exhibits insecticidal and 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'', 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, 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 (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'' * '' Artemisia tridentata'' * ''

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

'' * '' Eucalyptus largiflorens'' * '' 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