Eugenol /ˈjɪnɒl/ is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds.[2] It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove oil, nutmeg, cinnamon, basil and bay leaf.[3][4][5][6] It is present in concentrations of 80–90% in clove bud oil and at 82–88% in clove leaf oil.[7] Eugenol has a pleasant, spicy, clove-like scent.[8] The name is derived from Eugenia caryophyllata, the former Linnean nomenclature term for cloves. (The currently accepted name is Syzygium aromaticum.[9])

Skeletal formula of eugenol
Ball-and-stick model of the eugenol molecule
Preferred IUPAC name
Other names
  • 4-Allyl-2-methoxyphenol
  • 2-Methoxy-4-(2-propenyl)phenol
  • Eugenic acid
  • Caryophyllic acid
  • 1-Allyl-3-methoxy-4-hydroxybenzene
  • Allylguaiacol
  • 2-Methoxy-4-allylphenol
  • 4-Allylcatechol-2-methyl ether
3D model (JSmol)
ECHA InfoCard 100.002.355
Molar mass 164.204 g·mol−1
Density 1.06 g/cm3
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
−1.021×10−4 cm3/mol
  • 9.12 mPa·s at 20 °C
  • 5.99 mPa·s at 30 °C[1]
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point 104 °C (219 °F; 377 K)
Related compounds
Related compounds
2-Phenethyl propionate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Modern usesEdit

Eugenol is used in perfumes, flavorings, and essential oils. It is also used as a local antiseptic and anaesthetic.[10][11] Eugenol can be combined with zinc oxide to form zinc oxide eugenol which has restorative and prosthodontic applications in dentistry. For persons with a dry socket as a complication of tooth extraction, packing the dry socket with a eugenol-zinc oxide paste on iodoform gauze is effective for reducing acute pain.[12] Eugenol-zinc oxide paste is also used for root canal sealing.[13]

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.[14] It also attracts female cucumber beetles.[15] 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.[16]

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.[17][18] 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.[19]


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).[20] 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).[21] 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.

Biosynthesis of eugenol

Bioactivity and toxicityEdit

Eugenol and thymol were found to possess general anesthetic properties. Like many other anesthetic agents, these 2-alkyl(oxy)phenols were found to act as positive allosteric modulators of the GABAA receptor. Although eugenol and thymol are too toxic and not potent enough to use clinically, these findings led to the development of 2-substituted phenol anesthetic drugs, including propanidid (later withdrawn) and the widely used propofol.[22]

Eugenol is hepatotoxic, meaning it may cause damage to the liver.[23][24] 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.[25] According to a published 1993 report, a 2-year-old boy nearly died after taking between 5 and 10 ml.[26]


Eugenol is subject to restrictions on its use in perfumery[27] as some people may become sensitised to it, however, the degree to which eugenol can cause an allergic reaction in humans is disputed.[28]

Eugenol is a component of balsam of Peru, to which some people are allergic.[29][30] When eugenol is used in dental preparations such as surgical pastes, dental packing, and dental cement, it may cause contact stomatitis and allergic cheilitis.[29] The allergy can be discovered via a patch test.[29]

Natural occurrenceEdit

Eugenol naturally occurs in several plants, including the following:

See alsoEdit


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