Thymol

Thymol is produced by the alkylation of m-cresol and propene:^[7][8]

CH₃C₆H₄OH + CH₂CHCH₃ → ((CH₃)₂CH)CH₃C₆H₃OH

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 a cytochrome P450 in the CYP71D subfamily creates a dienol intermediate, which is then converted into a ketone by short-chain dehydrogenase. Lastly, keto-enol tautomerization gives thymol.

Ancient Egyptians used thyme for embalming.^[10] The ancient Greeks used it in their baths and burned it as incense in their temples, believing it was a source of courage. The spread of thyme throughout Europe was thought to be due to the Romans, as they used it to purify their rooms and to "give an aromatic flavour to cheese and liqueurs".^[11] In the European Middle Ages, the herb was placed beneath pillows to aid sleep and ward off nightmares.^[12] In this period, women also often gave knights and warriors gifts that included thyme leaves, because it was believed to bring courage to the bearer. Thyme was also used as incense and placed on coffins during funerals, because it was supposed to ensure passage into the next life.^[13]

The bee balms Monarda fistulosa and Monarda didyma, North American wildflowers, are natural sources of thymol. The Blackfoot Native Americans recognized these plants' strong antiseptic action and used poultices of the plants for skin infections and minor wounds. A tisane made from them was also used to treat mouth and throat infections caused by dental caries and gingivitis.^[14]

Thymol was first isolated by German chemist Caspar Neumann in 1719.^[15] In 1853, French chemist Alexandre Lallemand^[16] (1816-1886) named thymol and determined its empirical formula.^[17] Antiseptic properties of thymol were discovered in 1875,^[18] and it was first synthesized by Swedish chemist Oskar Widman^[19] (1852-1930) in 1882.^[20]

The conventional method of extracting is hydro-distillation (HD), but can also be extracted with solvent-free microwave 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.^[21]

Thymol during the 1910s was the treatment of choice for hookworm infection in the United States.^[22][23] People of the Middle East continue to use za'atar, a delicacy made with large amounts of thyme, to reduce and eliminate internal parasites.^[24] It is also used as a preservative in halothane, an anaesthetic, 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 with chlorhexidine than when used purely by itself.^[25] Thymol is also the active antiseptic ingredient in some toothpastes, such as Johnson & Johnson's Euthymol. Thymol has been used to successfully control varroa mites and prevent fermentation and the growth of mold in bee colonies.^[26] Thymol is also used as a rapidly degrading, non-persisting pesticides^[27] such as insecticides and fungicides which are leveraged in plant care products, where its environmentally friendly, rapid degradation ensures it doesn’t leave persistent residues while effectively controlling pests and fungal issues.^[28] Thymol can also be used as a medical disinfectant and general purpose disinfectant.^[29] Thymol is also used in the production of menthol through the hydrogenation of the aromatic ring.^[30]

• Illicium verum
• Euphrasia rostkoviana^[31]
• Lagoecia cuminoides^[32]
• Monarda didyma^[33]
• Monarda fistulosa^[34]
• Mosla chinensis
• Ocimum gratissimum L.^[35]
• Origanum compactum^[36]
• Origanum dictamnus^[37]
• Origanum onites^[38][39]
• Origanum vulgare^[40][41]
• Satureja hortensis
• Satureja thymbra
• Thymus glandulosus^[36]
• Thymus hyemalis^[42]
• Thymus serpyllum
• Thymus praecox
• Thymus vulgaris^[42][43]
• Thymus zygis^[44]
• Trachyspermum ammi

In 2009, the U.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".^[45]

• British Pharmacopoeia^[47]
• Japanese Pharmacopoeia^[48]

• Thymoquinone
• Nigella sativa
• Bromothymol