Eugenol is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds. 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. 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 scent. The name is derived from Eugenia caryophyllata, the former Linnean nomenclature term for cloves.
Modern uses
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 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. Eugenol-zinc oxide paste is also used for root canal sealing. 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 beetles. 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.
Eugenol and thymol were found to possess general anesthetic properties. Like many other anesthetic agents, these 2-alkylphenols 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 and the widely used propofol. 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.
Allergy
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.
Natural occurrence
Eugenol naturally occurs in several plants, including the following:
