|Preferred IUPAC name
3D model (JSmol)
|Molar mass||164.20 g·mol−1|
|Melting point||−7.5 °C (18.5 °F; 265.6 K)|
|Boiling point||254 °C (489 °F; 527 K)|
|Acidity (pKa)||10.19 at 25 °C|
|Flash point||104 °C (219 °F; 377 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Eugenol // is a phenylpropene, an allyl chain-substituted guaiacol. Eugenol is a member of the phenylpropanoids class of chemical compounds. It is a colourless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove oil, nutmeg, cinnamon, basil and bay leaf. It is present in concentrations of 80–90% in clove bud oil and at 82–88% in clove leaf oil. Eugenol has a pleasant, spicy, clove-like odor.
The name comes from Eugenia caryophyllata, a former scientific name for cloves.
Eugenol is used in perfumes, flavorings, and essential oils. It is also used as a local antiseptic and anaesthetic. Eugenol can be combined with zinc oxide to form zinc oxide eugenol which has restorative and prosthodontic applications in dentistry. For example, zinc oxide eugenol is used for root canal sealing.
Attempts have been made to develop eugenol derivatives as intravenous anesthetics, as an alternative to propanidid which produces unacceptable side effects around the site of injection in many patients.
It is one of many compounds that is attractive to males of various species of orchid bees, which apparently gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study. It also attracts female cucumber beetle. It was recently discovered that eugenol and isoeugenol, floral volatile scent compounds, are catalyzed by a single type of enzyme in the genus Gymnadenia and the gene encoding for this enzyme is the first functionally characterized gene in these species so far.
Clove oil is growing in popularity as an anaesthetic for use on aquarium fish as well as on wild fish when sampled for research and management purposes. Where readily available, it presents a humane method to euthanise sick and diseased fish either by direct overdose or to induce sleep before an overdose of eugenol.
The biosynthesis of eugenol begins with the amino acid tyrosine. L-tyrosine is converted to p-coumaric acid by the enzyme tyrosine ammonia lyase (TAL). From here, p-coumaric acid is converted to caffeic acid by p-coumarate 3-hydroxylase using oxygen and NADPH. S-Adenosyl methionine (SAM) is then used to methylate caffeic acid, forming ferulic acid, which is in turn converted to feruloyl-CoA by the enzyme 4-hydroxycinnamoyl-CoA ligase (4CL). Next, feruloyl-CoA is reduced to coniferaldehyde by cinnamoyl-CoA reductase (CCR). Coniferaldeyhyde is then further reduced to coniferyl alcohol by cinnamyl-alcohol dehydrogenase (CAD) or sinapyl-alcohol dehydrogenase (SAD). Coniferyl alcohol is then converted to an ester in the presence of the substrate CH3COSCoA, forming coniferyl acetate. Finally, coniferyl acetate is converted to eugenol via the enzyme eugenol synthase 1 and the use of NADPH.
Eugenol is hepatotoxic, meaning it may cause damage to the liver. Overdose is possible, causing a wide range of symptoms from blood in the patient's urine, to convulsions, diarrhoea, nausea, unconsciousness, dizziness, or rapid heartbeat. According to a published 1993 report, a 2-year-old boy nearly died after taking between 5 and 10 ml. In context, this would represent a toxic dose in the range of 500–1000 mg/kg, approximately one third that of table salt.
Eugenol is subject to restrictions on its use in perfumery as some people may become sensitised to it, however, the degree to which eugenol can cause an allergic reaction in humans is disputed.
Eugenol is a component of balsam of Peru, to which some people are allergic. When eugenol is used in dental preparations such as surgical pastes, dental packing, and dental cement, it may cause contact stomatitis and allergic cheilitis. The allergy can be discovered via a patch test.
Eugenol naturally occurs in several plants, including the following:
- Cloves (Syzygium aromaticum)
- Cinnamomum tamala
- Nutmeg (Myristica fragrans)
- Ocimum basilicum (sweet basil)
- Ocimum gratissimum (African basil)
- Ocimum tenuiflorum (syn. Ocimum sanctum, tulsi or holy basil)
- Japanese star anise
- Lemon balm
- Pimenta racemosa
- Bay laurel
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