|Jmol-3D images||Image 1|
|Molar mass||150.22 g mol−1|
|Melting point||51 °C (124 °F; 324 K)|
|Boiling point||232 °C (450 °F; 505 K)|
|Solubility in water||Insoluble|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Thymol (also known as 2-isopropyl-5-methylphenol, IPMP) is a natural monoterpene phenol derivative of cymene, C10H14O, isomeric with carvacrol, found in oil of thyme, and extracted from Thymus vulgaris (common thyme) and various other kinds of plants as a white crystalline substance of a pleasant aromatic odor and strong antiseptic properties. Thymol also provides the distinctive, strong flavor of the culinary herb thyme, also produced from T. vulgaris.
Thymol is part of a naturally occurring class of compounds known as biocides, with strong antimicrobial attributes when used alone or with other biocides such as carvacrol. In addition, naturally occurring biocidal agents such as thymol can reduce bacterial resistance to common drugs such as penicillin. Numerous studies have demonstrated the antimicrobial effects of thymol, ranging from inducing antibiotic susceptibility in drug-resistant pathogens to powerful antioxidant properties. Research demonstrates that naturally occurring biocides such as thymol and carvacrol reduce bacterial resistance to antibiotics through a synergistic effect, and thymol has been shown to be an effective fungicide, particularly against fluconazole-resistant strains. This is especially relevant given that opportunistic Candida fungal infections can cause severe systemic infections in immunocompromised patients, and current treatments are highly toxic, often result in drug-resistant Candida strains, and have low efficacy. Compounds in the essential oils of one type of oregano have demonstrated antimutagenic effects, and in particular carvacrol (isomeric with thymol) and thymol were demonstrated to have a strong antimutagenic effect. In addition, there is evidence that thymol has antitumor properties. Though the exact mechanism is unknown, some evidence suggests thymol effects at least some of its biocidal properties by membrane disruption.
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.
Synonyms include isopropyl-m-cresol, hydroxycymene, 1-methyl-3-hydroxy-4-isopropylbenzene, 2-hydroxy-1-isopropyl-4-methylbenzene; 3-hydroxy-p-cymene, 3-methyl-6-isopropylphenol, 5-methyl-2-(1-methylethyl)phenol, 5-methyl-2-isopropyl-1-phenol, 5-methyl-2-isopropylphenol, 6-isopropyl-3-methylphenol, 6-isopropyl-m-cresol, Apiguard, NSC 11215, NSC 47821, NSC 49142, thyme camphor, m-thymol, and p-cymen-3-ol.
The Ancient Egyptians used thymol and carvacrol in the form of a preparation from the thyme plant (a member of the mint family) to preserve mummies. Thymol and carvacrol are now known to kill bacteria and fungi, making thyme well suited for such purposes.
In Ancient Greece, thyme was widely used for its aromatic qualities, being burned as incense in sacred temples. Thyme was also a symbol of courage and admiration, with the phrase "the smell of thyme" being a saying that reflected praise unto its subject. Thyme's association with bravery continued throughout medieval times, when it was a ritual for women to give their knights a scarf that had a sprig of thyme placed over an embroidered bee. Since the 16th century, thyme oil has been used for its antiseptic properties, both as mouthwash and for topical application.
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.
Thymol was first isolated by the German chemist Caspar Neumann in 1719. In 1853, the French chemist A. Lallemand named thymol and determined its empirical formula. Thymol was first synthesized by the Swedish chemist Oskar Widman in 1882. Alain Thozet and M. Perrin first published the crystal structure analysis with the exact determination of the structural atoms.
Thymol has antimicrobial activity because of its phenolic structure, and has shown antibacterial activity against bacterial strains including Aeromoans hydrophila and Staphylococcus aureus. This antibacterial activity is caused by inhibiting growth and lactate production, and by decreasing cellular glucose uptake. Thymol has been used in alcohol solutions and in dusting powders for the treatment of tinea or ringworm infections, and was used in the United States to treat hookworm infections. 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. Thymol is also the active antiseptic ingredient in some toothpastes, such as Euthymol.
The antifungal nature of thymol is caused by thymol's ability to alter the hyphal morphology and cause hyphal aggregates, resulting in reduced hyphal diameters and lyses of hyphal wall. Additionally, thymol is lipophilic, enabling it to interact with the cell membrane of fungus cells, altering cell membrane permeability permitting the loss of macromolecules.
Derivatives of thymol and carvacrol with increased antimicrobial activities have been developed. The preparation of methacrylic and p-styrenesulfonic acid esters of thymol could lead to less toxic macromolecular biocides, which can be attached to a polymeric backbone.
A minor use of thymol is in book and paper conservation: Paper with mold damage can be sealed in bags with thymol crystals to kill fungal spores. However, this practice is not currently recommended due to apparent accelerated degradation suffered by these objects.
List of plants that contain thymol
- Monarda didyma
- Monarda fistulosa
- Trachyspermum ammi
- Origanum compactum
- Origanum dictamnus
- Origanum onites
- Origanum vulgare
- Thymus glandulosus
- Thymus hyemalis
- Thymus vulgaris
- Thymus zygis
Toxicology and environmental impacts
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".
Environmental breakdown and use as a pesticide
Studies have shown that hydrocarbon monoterpenes and thymol in particular degrade rapidly (DT50 16 days in water, 5 days in soil) in the environment and are, thus, low risks because of rapid dissipation and low bound residues, 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.
Notes and references
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