Methyl salicylate

Methyl salicylate (oil of wintergreen or wintergreen oil) is a natural product of many species of plants. Some of the plants which produce it are called wintergreens, hence the common name.

Botanical background

Plants containing methyl salicylate produce this organic ester (a combination of an organic acid with an alcohol) most likely 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.^[1] 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.^[2] Numerous plants produce methyl salicylate in very small amounts.

Plants producing it in significant amounts (readily detected by scent) include:

• most species of the family Pyrolaceae, particularly those in the genus Pyrola;
• 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.

Commercial production

Methyl salicylate can be produced by esterifying salicylic acid with methanol. 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

Methyl salicylate is used as a rubefacient in deep heating liniments (such as Bengay ointment), and in small amounts as a flavoring agent at no more than 0.04%.^[3] It is also used to provide fragrance to various products and as an odor-masking agent for some organophosphate pesticides. If applied in too high quantities it can cause stomach and kidney problems.^[4]

Methyl salicylate is among the compounds that attract male orchid bees, who apparently gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study.^[5]

Methyl salicylate has the ability 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.

Methyl salicylate, though its source plants are not true mints, is used as a mint in some kinds of chewing gum and candy, as an alternative to the more common peppermint and spearmint oils. It can also be found as a flavoring of root beer. It is also a potentially entertaining source of triboluminescence; when mixed with sugar and dried, it gains the tendency to build up electrical charge when crushed or rubbed. This effect can be observed by crushing wintergreen Life Savers candy in a dark room.^[6][7]

Methyl salicylate can be used as a transfer agent, to produce a manual copy of an image on a surface.^[8]

Methyl salicylate is added in small amounts to glacial acetic acid to lower its freezing point for transport in cold countries.

Methyl salicylate is used as a simulant or surrogate for the research of chemical warfare agent sulfur mustard, due to its similar chemical and physical properties.^[9]

Methyl salicylate is one of several antiseptic ingredients in Listerine mouthwash produced by the Johnson & Johnson company. It is also used in the "Dencorub Extra Strength" heat cream, which is used to treat joint and muscular pain and is a product of the Dencorub company.

Safety and toxicity

In pure form, methyl salicylate is toxic, especially when taken internally. A single teaspoon (5ml) of methyl salicylate contains 7g of salicylate,^[10] which is equivalent to more than twenty-three 300 mg aspirin tablets. The lowest published lethal dose is 101 mg/kg body weight in adult humans,^[11] (or 7.07 grams for a 70-kg adult). It has proven fatal to small children in doses as small as 4 ml.^[3] 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.^[12]

Most instances of human toxicity due to methyl salicylate are a result of over-application of topical analgesics, especially involving children. Some people have intentionally ingested large amounts of oil of wintergreen. 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.^[13]

Compendial status

• British Pharmacopoeia^[14]
• Japanese Pharmacopoeia^[15]

See also

• Mouthwash
• Salicylic acid
• Wintergreen
• Deep Heat (Heat_rub)

References

1. ^ D. G. James, T. S. Price (August 2004). "Field-testing of methyl salicylate for recruitment and retention of beneficial insects in grapes and hops". J. Chem. Ecol. 30 (8): 1613–28. doi:10.1023/B:JOEC.0000042072.18151.6f. PMID 15537163. 
2. ^ Vladimir Shulaev, Paul Silverman, Ilya Raskin (20 February 1997). "Airborne signalling by methyl salicylate in plant pathogen resistance". Nature 385 (6618): 718–721. doi:10.1038/385718a0. 
3. ^ ^{a b} Wintergreen at Drugs.com
4. ^ http://adam.about.com/encyclopedia/firstaid/Sports-cream-overdose.htm
5. ^ 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. 
6. ^ 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. 
7. ^ "Why do Wint-O-Green Life Savers spark in the dark?". HowStuffWorks. http://home.howstuffworks.com/question505.htm. 
8. ^ Image Transfer at Making-greeting-cards.com
9. ^ Bartlet-Hunt, S. L.; Knappe, Detlef R. U. et al. (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. 
10. ^ Salicylate Poisoning - Patient UK
11. ^ Safety data for methyl salicylate, Physical & Theoretical Chemistry Laboratory, Oxford University
12. ^ "Muscle-Pain Reliever Is Blamed For Staten Island Runner’s Death". New York Times. 10 June 2007. http://www.nytimes.com/2007/06/10/nyregion/10cream.html?_r=1&ref=nyregion&oref=slogin. 
13. ^ Baselt, R. (2008). Disposition of Toxic Drugs and Chemicals in Man (8th ed.). Foster City, CA: Biomedical Publications. pp. 1012–1014. ISBN 9780962652370. 
14. ^ The British Pharmacopoeia Secretariat (2009). "Index, BP 2009". http://www.pharmacopoeia.co.uk/pdf/2009_index.pdf. Retrieved 5 July 2009. 
15. ^ NIHS Japan

External links

Toxicity

• MedlinePlus - Methyl salicylate overdose
• MedlinePlus - Sports cream overdose
• CNN - Medical examiner: Sports cream caused teen's death Wayback machine link to this article
• NLM Hazardous Substances Databank – Methyl salicylate