 Eucalyptol is a natural organic compound which is a colorless liquid. It is a cyclic ether and a monoterpenoid.
Eucalyptol is also known by a variety of synonyms: 1,8-cineol, 1,8-cineole, limonene oxide, cajeputol, 1,8-epoxy-p-menthane, 1,8-oxido-p-menthane, eucalyptol, eucalyptole, 1,3,3-trimethyl-2-oxabicyclo[2,2,2]octane, cineol, cineole.
Composition
Eucalyptol comprises up to 90 percent of the essential oil of some species of Eucalyptus (e.g. Eucalyptus polybractea), hence the common name of the compound. It is also found in bay leaves, mugwort, sweet basil, wormwood, rosemary, sage and other aromatic plant foliage. Eucalyptol with a purity from 99.6 to 99.8 percent can be obtained in large quantities by fractional distillation of eucalyptus oil.
In common with many essential oils (volatile oils), eucalyptus oil is toxic if ingested internally.
Properties
Eucalyptol has a fresh camphor-like smell and a spicy, cooling taste. It is insoluble in water, but miscible with ether, ethanol and chloroform. The boiling point is 176 °C and the flash point is 49 °C.
Uses
Because of its pleasant spicy aroma and taste, eucalyptol is used in flavorings, fragrances, and cosmetics. It is also an ingredient in many brands of mouthwash and cough suppressant. Eucalyptol has been demonstrated to be capable of reducing inflammation and pain. It has also been found to be able to kill leukaemic cells in vitro.
Cineol was shown to be an effective treatment for nonpurulent rhinosinusitis in a placebo controlled trial. 76 patients per treatment group were assigned to cineole or placebo. The dosage of the active ingredient was two 100 mg capsules of cineole three times daily. Symptom scores were significantly reduced in the cineole group. The mean values for the symptoms-sum-scores in the cineole group were 6.9 ± 2.9 after 4 days and 3.0 ± 2.8 after 7 days, and in the placebo group, 12.2 ± 2.5 after 4 days and 9.2 ± 3.0 after 7 days. Treated subjects experienced less headache on bending, frontal headache, sensitivity of pressure points of trigeminal nerve, impairment of general condition, nasal obstruction, and rhinological secretion. Side effects from treatment were minimal.
In a 1994 report released by five top cigarette companies, eucalyptol was listed as one of the 599 additives to cigarettes. It is added to improve the flavor.
It is one of many compounds that is attractive to males of various species of orchid bees, who apparently gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study.
Eucalyptus oil can also be used as an effective way of killing dust mites according to the Asthma Foundation of Victoria.
Although there are over 500 species of the eucalyptus tree worldwide, eucalyptol can be mainly found in Australia as the Australian Gum Tree.
Eucalyptus
Eucalyptus (From Greek, ευκάλυπτος meaning "well covered") is a diverse genus of trees (and a few shrubs), the members of which dominate the tree flora of Australia. There are more than seven hundred species of Eucalyptus, mostly native to Australia, with a very small number found in adjacent parts of New Guinea and Indonesia and one as far north as the Philippines islands. Many Eucalyptus have been planted in various parts of the world including the dry regions of Southern California and in Africa, Portugal, Spain, South America, and on forestry plantations in India and China.
Members of the genus can be found in almost every region of the Australian continent, because they have adapted to all of its climatic conditions; in fact no other continent is so characterised by a single genus of tree as Australia is by its eucalyptus. Many, but far from all, are known as gum trees in reference to the habit of many species to exude copious sap from any break in the bark (e.g. Scribbly Gum).
Size and habit
A Eucalyptus may be mature as a low shrub or as a very large tree. There are three main habit and four size categories that species can be divided into.
As a generalisation "forest trees" are single-stemmed and have a crown forming a minor proportion of the whole tree height. "Woodland trees" are single-stemmed although they may branch at a short distance above ground level.
"Mallees" are multi-stemmed from ground level, usually less than 10 metres in height, often with the crown predominantly at the ends of the branchlets and individual plants may combine to form either an open or closed formation. Many mallee trees may be so low growing as to be considered a shrub.
Apart from the forest tree, woodland tree, mallee and shrub habits two further tree forms are notable in Western Australia. One of these is the "mallet", which is a small to medium-sized tree, usually of steep branching habit, sometimes fluted at the base of the trunk and often with a conspicuously dense, terminal crown. It is the habit usually of mature healthy specimens of Eucalyptus occidentalis, E. astringens, E. spathulata, E. gardneri, E. dielsii, E. forrestiana, E. salubris, E. clivicola and E. ornata. The smooth bark of mallets often has a satiny sheen and may be white, cream, grey, green or copper.
Another habit category used in Western Australia is the "marlock". This has been variously applied but Brooker & Hopper (2001) defined the term and restricted the use to describe the more or less pure stands of short, erect, thin-stemmed "trees" that do not produce lignotubers. These are easily seen and recognised in stands of E. platypus, E. vesiculosa and the unrelated E. stoatei. The marlock is distinguished from mallets which are taller and have a characteristic steep branching habit. The origin and use of the term "morrel" is somewhat obscure and appears to apply to trees of the western Australian wheatbelt and goldfields which have a long, straight trunk, completely rough barked. It is now used mainly for E. longicornis (Red Morell) and E. melanoxylon (Black Morrel).
Tree sizes follow the convention of:- Small - to 10 metres in height.
- Medium sized - 10 to 30 metres in height.
- Tall - 30 to 60 metres in height.
- Very Tall - over 60 metres in height.
Leaves
Nearly all Eucalyptus are evergreen but some tropical species lose their leaves at the end of the dry season. As in other members of the Myrtle family, Eucalyptus leaves are covered with oil glands. The copious oils produced are an important feature of the genus.
The leaves on a mature Eucalyptus plant are commonly lanceolate, petiolate, apparently alternate and waxy or glossy green. In contrast the leaves of seedlings are frequently opposite, sessile and glaucous. However there are numerous exceptions to this pattern. Many species such as E. melanophloia and E. setosa retain the juvenile leaf form even when the plant is reproductively mature. Some species such as E. macrocarpa, E. rhodantha and E. crucis are sought after ornamentals due to this lifelong juvenile leaf form. A few species such as E. petraea, E. dundasii and E. lansdowneana have shiny green leaves throughout their life cycle. E. caesia exhibits the opposite pattern of leaf development to most Eucalyptus, with shiny green leaves in the seedling stage and dull, glaucous leaves in mature crowns. The contrast between juvenile and adult leaf phases is valuable in field identification.
Four leaf phases are recognised in the development of a Eucalyptus plant - the ‘seedling’, ‘juvenile’, ‘intermediate’ and ‘adult’ phases. However there is no definite transitional point between the phases. The intermediate phase, when the largest leaves are often formed, links the juvenile and adult phases.
In all except a few species the leaves form in pairs on opposite sides of a square stem, consecutive pairs being at right angles to each other (decussate). In some narrow-leaved species - for example E. oleosa - the seedling leaves after the second leaf pair are often clustered in a detectable spiral arrangement about a five sided stem. After the spiral phase, which may last from several to many nodes, the arrangement reverts to decussate by the absorption of some of the leaf bearing faces of the stem. In those species with opposite adult foliage the leaf pairs, which have been formed opposite at the stem apex, become separated at their bases by unequal elongation of the stem to produce the apparently alternate adult leaves.
Flowers
The most readily recognisable characteristics of Eucalyptus species are its distinctive flowers and fruit (capsule). Flowers have numerous fluffy stamens which may be white, cream, yellow, pink or red; in bud the stamens are enclosed in a cap known as an operculum which is composed of the fused sepals or petals or both. Thus flowers have no petals, decorating themselves instead with the many showy stamens. As the stamens expand the operculum is forced off, splitting away from the cup-like base of the flower; this is one of the features that unites the genus. The name Eucalyptus, from the Greek words eu-, well, and kaluptos, cover, meaning "well-covered", describes the operculum. The woody fruits or capsules, known as gumnuts, are roughly cone-shaped and have valves at the end which open to release the seeds. Most species do not flower until adult foliage starts to appear; Eucalyptus cinerea and Eucalyptus perriniana are notable exceptions.
Bark
The appearance of Eucalyptus bark will vary with the age of the plant, the manner of bark shed, the length of the bark fibres, the degree of furrowing, the thickness, the hardness and the colour. All mature eucalypts put on an annual layer of bark, which contributes to the increasing diameter of the stems. In some species the outermost layer dies and is annually deciduous either in long strips (as in Eucalyptus sheathiana) or in variably sized flakes (Eucalyptus diversicolor, Eucalyptus cosmophylla or Eucalyptus cladocalyx). These are the gums or smooth-barked species. The gum bark may be dull, shiny or satiny (as in Eucalyptus ornata) or matt (Eucalyptus cosmophylla). In many species the dead bark is retained. Its outermost layer gradually fragments with weathering and sheds without altering the essentially rough barked nature of the trunks or stems - for example Eucalyptus marginata, Eucalyptus jacksonii, Eucalyptus obliqua and Eucalyptus porosa.
Many species are ‘half-barks’ or ‘blackbutts’ in which the dead bark is retained in the lower half of the trunks or stems - for example, Eucalyptus brachycalyx, Eucalyptus ochrophloia and Eucalyptus occidentalis - or only in a thick, black accumulation at the base, as in Eucalyptus clelandii. Some species in this category - for example - Eucalyptus youngiana - the rough basal bark is very ribbony at the top, where it gives way to the smooth upper stems. The smooth upper bark of the half barks and that of the completely smooth-barked trees and mallees can produce remarkable colour and interest, for example Eucalyptus deglupta.
Bark characteristics- Stringybark - consists of long-fibres and can be pulled off in long pieces. It is usually thick with a spongy texture.
- Ironbark - is hard, rough and deeply furrowed. It is impregnated with dried kino (a sap exuded by the tree) which gives a dark red or even black colour.
- Tessellated - bark is broken up into many distinct flakes. They are corkish and can flake off.
- Box - has short fibres. Some also show tessellation.
- Ribbon - this has the bark coming off in long thin pieces but still loosely attached in some places. They can be long ribbons, firmer strips or twisted curls.
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Essential
Oil
