Thymol provides the distinctive flavor of theculinary herb thyme, also produced fromT. vulgaris.[4] Thymol is only slightlysoluble in water at neutralpH, but due todeprotonation of thephenol, it is highly soluble inalcohols, other organic solvents, and stronglyalkaline aqueous solutions.
A predicted method of biosynthesis of thymol in thyme and oregano begins with the cyclization of geranyl diphosphate by TvTPS2 to γ-terpinene. Oxidation by acytochrome P450 in the CYP71D subfamily creates adienol intermediate, which is then converted into a ketone by short-chain dehydrogenase. Lastly,keto-enol tautomerization gives thymol. Its dissociation constant (pKa) is10.59±0.10.[8] Thymol absorbs maximumUV radiation at 274 nm.[9]
Thymol was first isolated by German chemistCaspar Neumann in 1719.[11] In 1853, French chemist Alexandre Lallemand[12] (1816-1886) named thymol and determined its empirical formula.[13] Possibleantiseptic properties of thymol were discovered in 1875,[14] and it was first synthesized by Swedish chemist Oskar Widman (1852-1930) in 1882.[15]
The conventional method ofextracting ishydro-distillation (HD), but can also be extracted withsolvent-freemicrowave extraction (SFME). In 30 minutes, SFME yields similar amounts of thymol with more oxygenated compounds than 4.5 hours of hydro-distillation at atmospheric pressures without the need for solvent.[16]
Predicted biosynthesis of thymol in thyme and oregano. Reconstruction of figure 4 in Krause et. al. (2021).[17]
During the 1910s, thymol was used forhookworm infection in the United States.[18][19] People of the Middle East continue to useza'atar, a delicacy made with large amounts of thyme, to reduce and eliminate internal parasites.[20] It is also used as apreservative inhalothane, ananaesthetic, and as an antiseptic in mouthwash. When used to reduce plaque and gingivitis, thymol has been found to be more effective when used in combination withchlorhexidine than when used purely by itself.[21]
Thymol is a fragrance ingredient in somecosmetics.[4] Thymol has been used to successfully controlvarroa mites and prevent fermentation and the growth ofmold inbee colonies.[22] Thymol is also used as a rapidly degrading, non-persistingpesticide,[4][23] such as insecticides and fungicides which are leveraged in plant care products. Thymol can also be used as a medical disinfectant and general purposedisinfectant.[24] Thymol is also used in the production ofmenthol through the hydrogenation of the aromatic ring.[25]
In 2009, theU.S. Environmental Protection Agency (EPA) reviewed the research literature on the toxicology and environmental impact of thymol and concluded that "thymol has minimal potential toxicity and poses minimal risk".[40]
Studies have shown that hydrocarbonmonoterpenes and thymol in particular degrade rapidly (DT50 16 days in water, 5 days in soil[23]) in the environment and are, thus, low risks because of rapid dissipation and low bound residues,[23] supporting the use of thymol as a pesticide agent that offers a safe alternative to other more persistent chemical pesticides that can be dispersed in runoff and produce subsequent contamination. Though, there has been recent research into sustained released systems for botanically derived pesticides, such as using naturalpolysaccharides which would be biodegradable and biocompatible.[41]
^Norwitz G, Nataro N, Keliher PN (1986). "Study of the Steam Distillation of Phenolic Compounds Using Ultraviolent Spectrometry".Anal. Chem.58 (639–640): 641.doi:10.1021/ac00294a034.
^Tilford GL (1997).Edible and Medicinal Plants of the West. Missoula, MT: Mountain Press Publishing.ISBN978-0-87842-359-0.
^Neuman C (1724)."De Camphora".Philosophical Transactions of the Royal Society of London.33 (389):321–332.doi:10.1098/rstl.1724.0061. On page 324, Neumann mentions that in 1719 he distilled some essential oils from various herbs. On page 326, he mentions that during these experiments, he obtained a crystalline substance from thyme oil, which he called "Camphora Thymi" (camphor of thyme). (Neumann gave the name "camphor" not only to the specific substance that today is called camphor but to any crystalline substance that precipitated from a volatile, fragrant oil from some plant.)
^Marie-Étienne-Alexandre Lallemand (25 December 1816 – 16 March 1886)
^Ferrell JA (1914).The Rural School and Hookworm Disease. US Bureau of Education Bulletin. Vol. 20, Whole No. 593. Washington, DC: U.S. Government Printing Office.
^Baser KH, Tümen G (1994). "Composition of the Essential Oil ofLagoecia cuminoides L. from Turkey".Journal of Essential Oil Research.6 (5):545–546.doi:10.1080/10412905.1994.9698448.
^abBouchra C, Achouri M, Idrissi Hassani LM, et al. (2003). "Chemical composition and antifungal activity of essential oils of seven Moroccan Labiatae againstBotrytis cinerea Pers: Fr".Journal of Ethnopharmacology.89 (1):165–169.doi:10.1016/S0378-8741(03)00275-7.PMID14522450.
^Liolios CC, Gortzi O, Lalas S, et al. (2009). "Liposomal incorporation of carvacrol and thymol isolated from the essential oil ofOriganum dictamnus L. and in vitro antimicrobial activity".Food Chemistry.112 (1):77–83.doi:10.1016/j.foodchem.2008.05.060.
^Ozkan G, Baydar H, Erbas S (2009). "The influence of harvest time on essential oil composition, phenolic constituents and antioxidant properties of Turkish oregano (Origanum onites L.)".Journal of the Science of Food and Agriculture.90 (2):205–209.doi:10.1002/jsfa.3788.PMID20355032.
^Lagouri V, Blekas G, Tsimidou M, et al. (1993). "Composition and antioxidant activity of essential oils from Oregano plants grown wild in Greece".Zeitschrift für Lebensmittel-Untersuchung und -Forschung A.197 (1):1431–4630.doi:10.1007/BF01202694.S2CID81307357.
^Kanias GD, Souleles C, Loukis A, et al. (1998). "Trace elements and essential oil composition in chemotypes of the aromatic plantOriganum vulgare".Journal of Radioanalytical and Nuclear Chemistry.227 (1–2):23–31.Bibcode:1998JRNC..227...23K.doi:10.1007/BF02386426.S2CID94582250.
^Figiel A, Szumny A, Gutiérrez Ortíz A, et al. (2010). "Composition of oregano essential oil (Origanum vulgare) as affected by drying method".Journal of Food Engineering.98 (2):240–247.doi:10.1016/j.jfoodeng.2010.01.002.
^abGoodner K, Mahattanatawee K, Plotto A, et al. (2006). "Aromatic profiles ofThymus hyemalis and SpanishT. vulgaris essential oils by GC–MS/GC–O".Industrial Crops and Products.24 (3):264–268.doi:10.1016/j.indcrop.2006.06.006.
^Lee SJ, Umano K, Shibamoto T, et al. (2005). "Identification of volatile components in basil (Ocimum basilicum L.) and thyme leaves (Thymus vulgaris L.) and their antioxidant properties".Food Chemistry.91 (1):131–137.doi:10.1016/j.foodchem.2004.05.056.
^Moldão Martins M, Palavra A, Beirão da Costa ML, et al. (2000). "Supercritical CO2 extraction ofThymus zygis L. subsp.sylvestris aroma".The Journal of Supercritical Fluids.18 (1):25–34.doi:10.1016/S0896-8446(00)00047-4.
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