Thymol is only slightly soluble in water at neutral pH, but it is extremely soluble in alcohols and other organic solvents. It is also soluble in strongly alkaline aqueous solutions due to deprotonation of the phenol.

Thymol has a refractive index of 1.5208^[4] and an experimental dissociation exponent (pK_a) of 10.59±0.10.^[5] Thymol absorbs maximum UV radiation at 274 nm.^[6]

Chemical synthesisEdit

Regions lacking natural sources of thymol obtain the compound via total synthesis.^[7] Thymol is produced from m-cresol and propene in the gas phase:^[8]

C₇H₈O + C₃H₆ ⇌ C₁₀H₁₄O

Ancient Egyptians used thyme for embalming.^[9] 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".^[10] In the European Middle Ages, the herb was placed beneath pillows to aid sleep and ward off nightmares.^[11] 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.^[12]

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.^[13]

Thymol was first isolated by German chemist Caspar Neumann in 1719.^[14] In 1853, French chemist Alexandre Lallemand named thymol and determined its empirical formula.^[15] Thymol was first synthesized by Swedish chemist Oskar Widman in 1882.^[16]

An in vitro study found thymol and carvacrol to be highly effective in reducing the minimum inhibitory concentration of several antibiotics against zoonotic pathogens and food spoilage bacteria such as Salmonella typhimurium SGI 1 and Streptococcus pyogenes ermB.^[17] In vitro studies have found thymol to be useful as an antifungal against food spoilage and bovine mastitis.^[18] Thymol demonstrates in vitro post-antibacterial effect against the test strains E. coli and P. aeruginosa (gram negative), and Staphylococcus aureus and B. cereus (gram positive).^[19] This antibacterial activity is caused by inhibiting growth and lactate production, and by decreasing cellular glucose uptake.^[20]

Thyme essential oil is useful in preservation of food. The antibacterial properties of thymol, a major part of thyme essential oil, as well as other constituents, are in part associated with their lipophilic character, leading to accumulation in bacterial membranes and subsequent membrane-associated events, such as energy depletion.^[21]

The antifungal nature of thymol against some fungi that are pathogenic to plants is due to its ability to alter the hyphal morphology and cause hyphal aggregates, resulting in reduced hyphal diameters and lyses of the hyphal wall.^[22]

Thymol has been used in alcohol solutions and in dusting powders for the treatment of tinea or ringworm infections, and during the 1910s was the treatment of choice for hookworm infection in the United States.^[23][24] People of the Middle East continue to use za'atar, a delicacy made with large amounts of thyme, to reduce and eliminate internal parasites.^[25] 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.^[26] 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.^[27] Thymol is also used as a rapidly degrading, non-persisting pesticide.^[18][28] Thymol can also be used as a medical disinfectant and general purpose disinfectant.^[29]

• Illicium verum
• Euphrasia rostkoviana^[30]
• Lagoecia cuminoides^[31]
• Monarda didyma^[32]
• Monarda fistulosa^[33]
• Mosla chinensis, Xiang Ru (香薷)
• Origanum compactum^[34]
• Origanum dictamnus^[35]
• Origanum onites^[36][37]
• Origanum vulgare^[38][39]
• Satureja thymbra
• Thymus glandulosus^[34]
• Thymus hyemalis^[40]
• Thymus vulgaris^[40][41]
• Thymus zygis^[42]
• 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".^[43]

Environmental breakdown and use as a pesticideEdit

Studies have shown that hydrocarbon monoterpenes and thymol in particular degrade rapidly (DT₅₀ 16 days in water, 5 days in soil^[28]) in the environment and are, thus, low risks because of rapid dissipation and low bound residues,^[28] 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.

• British Pharmacopoeia^[44]
• Japanese Pharmacopoeia^[45]

• Thymoquinone
• Nigella sativa
• Bromothymol

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