Methyl salicylate

Methyl salicylate (oil of wintergreen or wintergreen oil) is an organic compound with the formula C6H4(OH)(CO2CH3). It is the methyl ester of salicylic acid. It is a colorless, viscous liquid with a sweet fruity odor reminiscent of root beer.[4] The odor is often described as "minty" due to its use in mint candies. It is produced by many species of plants, particularly wintergreens. It is also produced synthetically, used as a fragrance, in foods and beverages, and in liniments.

Methyl salicylate
Ball-and-stick model
Space-filling model
Names
IUPAC name
Methyl 2-hydroxybenzoate
Other names
  • Salicylic acid methyl ester
  • Oil of wintergreen
  • Betula oil
  • Methyl 2-hydroxybenzoate
Identifiers
CAS Number
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.003.925
EC Number
  • 204-317-7
KEGG
PubChem CID
RTECS number
  • VO4725000
UNII
Properties
Chemical formula
 C8H8O3
Molar mass 152.149 g·mol−1
Appearance Colorless liquid
Odor sweet, rooty
Density 1.174 g/cm3
Melting point −8.6 °C (16.5 °F; 264.5 K)
Boiling point 222 °C (432 °F; 495 K) [1]
Decomposes at 340–350 °C[2]
Solubility in water
 0.639 g/L (21 °C)
0.697 g/L (30 °C)[2]
Solubility Miscible in organic solvents
Solubility in acetone 10.1 g/g (30 °C)[2]
Vapor pressure 1 mmHg (54 °C)[1]
Acidity (pKa) 9.8[3]
Magnetic susceptibility (χ)
 −8.630×10−5 cm3/mol
Refractive index (nD)
 1.538
Hazards
Main hazards Harmful
GHS pictograms [1]
GHS Signal word Warning
GHS hazard statements
 H302[1]
GHS precautionary statements
 P264, P270, P280, P301+312, P302+352, P305+351+338, P321, P330, P332+313, P337+313, P362, P501
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
2
0
Flash point 96 °C (205 °F; 369 K) [1]
Autoignition
temperature
 452.7 °C (846.9 °F; 725.8 K)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Biosynthesis and occurrence

Methyl salicylate was first isolated (from the plant Gaultheria procumbens) in 1843 by the French chemist Auguste André Thomas Cahours (1813–1891), who identified it as an ester of salicylic acid and methanol.[5][6]

Wintergreen plants (Gaultheria procumbens)

The biosynthesis of methyl salicylate arises via the hydroxylation of benzoic acid by a cytochrome P450 followed by methylation by a methylase enzyme.[7]

Methyl salicylate is probably produced as an anti-herbivore defense. If the plant is infected with herbivorous insects, the release of methyl salicylate may function as an aid in the recruitment of beneficial insects to kill the herbivorous insects.[8] Aside from its toxicity, methyl salicylate may also be used by plants as a pheromone to warn other plants of pathogens such as tobacco mosaic virus.[9]

Numerous plants produce methyl salicylate in very small amounts. Some plants, such as the following, produce more: some species of the genus Gaultheria in the family Ericaceae, including Gaultheria procumbens, the wintergreen or eastern teaberry; some species of the genus Betula in the family Betulaceae, particularly those in the subgenus Betulenta such as B. lenta, the black birch; all species of the genus Spiraea in the family Rosaceae, also called the meadowsweets; species of the genus Polygala in the family Polygalaceae.

Commercial production

Methyl salicylate can be produced by esterifying salicylic acid with methanol.[10] Commercial methyl salicylate is now synthesized, but in the past, it was commonly distilled from the twigs of Betula lenta (sweet birch) and Gaultheria procumbens (eastern teaberry or wintergreen).

Uses
Chick embryo that was treated with methylene blue to stain the skeleton, then cleansed with two or three ethanol washes, and treated with methyl salicylate to make the surrounding tissues transparent

Methyl salicylate is used in high concentrations as a rubefacient and analgesic in deep heating liniments (such as Bengay) to treat joint and muscular pain. Randomised double blind trials report that evidence of its effectiveness is weak, but stronger for acute pain than chronic pain, and that effectiveness may be due entirely to counterirritation. However, in the body it metabolizes into salicylates, including salicylic acid, a known NSAID.[11][12][13]

Methyl salicylate is used in low concentrations (0.04% and under)[14] as a flavoring agent in chewing gum and mints. When mixed with sugar and dried it is a potentially entertaining source of triboluminescence, gaining the tendency to build up electrical charge when crushed or rubbed. This effect can be observed by crushing wintergreen Life Savers in a dark room.[15][16] It is used as an antiseptic in Listerine mouthwash produced by the Johnson & Johnson company.[17] It provides fragrance to various products and as an odor-masking agent for some organophosphate pesticides.

Methyl salicylate is also used as a bait for attracting male orchid bees for study, which apparently gather the chemical to synthesize pheromones,[18] and to clear plant or animal tissue samples of color, and as such is useful for microscopy and immunohistochemistry when excess pigments obscure structures or block light in the tissue being examined. This clearing generally only takes a few minutes, but the tissue must first be dehydrated in alcohol.[19]

Additional applications include used as a simulant or surrogate for the research of chemical warfare agent sulfur mustard, due to its similar chemical and physical properties.[20], in restoring (at least temporarily) the elastomeric properties of old rubber rollers, especially in printers, [21] and as a penetrating oil to loosen rusted parts.

Safety and toxicity

Methyl salicylate is potentially deadly, especially for young children. A single teaspoon (5 ml) of methyl salicylate contains approximately 6 g of salicylate,[22] which is equivalent to almost twenty 300 mg aspirin tablets (5 mL × 1.174 g/mL = 5.87 g). Toxic ingestions of salicylates typically occur with doses of approximately 150 mg/kg body weight. This can be achieved with 1 ml of oil of wintergreen, which equates to 140 mg/kg of salicylates for a 10 kg child (22 lbs).[23] The lowest published lethal dose is 101 mg/kg body weight in adult humans,[24] (or 7.07 grams for a 70 kg adult). It has proven fatal to small children in doses as small as 4 ml.[14] A seventeen-year-old cross-country runner at Notre Dame Academy on Staten Island died in April 2007 after her body absorbed methyl salicylate through excessive use of topical muscle-pain relief products.[25]

Most instances of human toxicity due to methyl salicylate are a result of over-application of topical analgesics, especially involving children. Salicylate, the major metabolite of methyl salicylate, may be quantitated in blood, plasma or serum to confirm a diagnosis of poisoning in hospitalized patients or to assist in an autopsy.[26]

Compendial status

See also

References
  1. Sigma-Aldrich Co., Methyl salicylate. Retrieved on 2013-05-23.
  2. "Methyl salicylate". chemister.ru.
  3. Scully, F. E.; Hoigné, J. (January 1987). "Rate constants for reactions of singlet oxygen with phenols and other compounds in water". Chemosphere. 16 (4): 681–694. Bibcode:1987Chmsp..16..681S. doi:10.1016/0045-6535(87)90004-X.
  5. Cahours, A. A. T. (1843). "Recherches sur l'huile de Gaultheria procumbens" [Investigations into the oil of Gaultheria procumbens]. Comptes Rendus. 16: 853–856.
  6. Cahours, A. A. T. (1843). "Sur quelques réactions du salicylate de méthylène" [On some reactions of methyl salicylate]. Comptes Rendus. 17: 43–47.
  7. Vogt, T. (2010). "Phenylpropanoid Biosynthesis". Molecular Plant: 2–20. doi:10.1093/mp/ssp106.
  8. James, D. G.; Price, T. S. (2004). "Field-testing of methyl salicylate for recruitment and retention of beneficial insects in grapes and hops". Journal of Chemical Ecology. 30 (8): 1613–1628. doi:10.1023/B:JOEC.0000042072.18151.6f. PMID 15537163.
  9. Shulaev, V.; Silverman, P.; Raskin, I. (1997). "Airborne signalling by methyl salicylate in plant pathogen resistance". Nature. 385 (6618): 718–721. Bibcode:1997Natur.385..718S. doi:10.1038/385718a0.
  10. Boullard, Olivier; Leblanc, Henri; Besson, Bernard (2012). "Salicylic Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a23_477.
  11. "Topical analgesics introduction". Medicine.ox.ac.uk. 2003-05-26. Archived from the original on 2012-08-04. Retrieved 2012-11-07.
  12. Mason, L.; Moore, R. A.; Edwards, J. E.; McQuay, H. J.; Derry, S.; Wiffen, P. J. (2004). "Systematic review of efficacy of topical rubefacients containing salicylates for the treatment of acute and chronic pain". British Medical Journal. 328 (7446): 995. doi:10.1136/bmj.38040.607141.EE. PMC 404501. PMID 15033879.
  13. Tramer, M. R. (2004). "It's not just about rubbing--topical capsaicin and topical salicylates may be useful as adjuvants to conventional pain treatment". British Medical Journal. 328 (7446): 998. doi:10.1136/bmj.328.7446.998. PMC 404503. PMID 15105325.
  14. Wintergreen at Drugs.com
  15. Harvey, E. N. (1939). "The luminescence of sugar wafers". Science. 90 (2324): 35–36. Bibcode:1939Sci....90...35N. doi:10.1126/science.90.2324.35. PMID 17798129.
  16. "Why do Wint-O-Green Life Savers spark in the dark?". HowStuffWorks.
  17. Listerine. "Original Listerine Antiseptic Mouthwash". Retrieved 25 March 2015.
  18. Schiestl, F. P.; Roubik, D. W. (2004). "Odor Compound Detection in Male Euglossine Bees". Journal of Chemical Ecology. 29 (1): 253–257. doi:10.1023/A:1021932131526. PMID 12647866.
  19. Altman, J. S.; Tyrer, N. M. (1980). "Filling selected neurons with cobalt through cut axons". In Strausfeld, N. J.; Miller, T. A. (eds.). Neuroanatomical Techniques. Springer-Verlag. pp. 373–402.
  20. Bartlet-Hunt, S. L.; Knappe, D. R. U.; Barlaz, M. A. (2008). "A Review of Chemical Warfare Agent Simulants for the Study of Environmental Behaviour". Critical Reviews in Environmental Science and Technology. 38 (2): 112–136. doi:10.1080/10643380701643650.
  21. "MG Chemicals – Rubber Renue Safety Data Sheet" (PDF). Archived from the original (PDF) on 2015-06-26.
  22. "Salicylate Poisoning – Patient UK". Patient.info. 2011-04-20. Retrieved 2013-07-01.
  23. Hoffman, R. (2015). Goldfrank's Toxicologic Emergencies (10th ed.). New York, NY: McGraw-Hill. pp. 915–922. ISBN 978-0-07-180184-3.
  24. Safety data for methyl salicylate, Physical & Theoretical Chemistry Laboratory, Oxford University
  25. "Muscle-Pain Reliever Is Blamed For Staten Island Runner's Death". New York Times. 10 June 2007.
  26. Baselt, R. (2008). Disposition of Toxic Drugs and Chemicals in Man (8th ed.). Foster City, CA: Biomedical Publications. pp. 1012–1014. ISBN 978-0-9626523-7-0.
  27. The British Pharmacopoeia Secretariat (2009). "Index, BP 2009" (PDF). Archived from the original (PDF) on 11 April 2009. Retrieved 5 July 2009.
  28. "NIHS Japan". Moldb.nihs.go.jp. Retrieved 2013-07-01.
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