Methyl salicylate (oil of wintergreen or wintergreen oil) is an
organic compound with the formula C8H8O3. It is the methyl
ester of
salicylic acid. It is a colorless,
viscous liquid with a sweet, fruity odor reminiscent of
root beer (in which it is used as a flavoring),[4] but often
associatively called "minty", as it is an ingredient in mint candies.[5] It is produced by many species of
plants, particularly
wintergreens. It is also produced synthetically, used as a
fragrance and as a flavoring agent.
Many plants produce methyl salicylate in small quantities. Methyl salicylate levels are often upregulated in response to biotic stress, especially infection by pathogens, where it plays a role in the induction of
resistance. Methyl salicylate is believed to function by being metabolized to the plant hormone salicylic acid. Since methyl salicylate is volatile, these signals can spread through the air to distal parts of the same plant or even to neighboring plants, whereupon they can function as a mechanism of
plant-to-plant communication, "warning" neighbors of danger.[9] Methyl salicylate is also released in some plants when they are damaged by herbivorous insects, where they may function as a cue aiding in the recruitment of predators.[10]
Some plants produce methyl salicylate in larger quantities, where it likely involved in direct defense against predators or pathogens. Examples of this latter class include: 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. Methyl salicylate can also be a component of
floral scents, especially in plants dependent on nocturnal pollinators like moths,[11] scarab beetles, and (nocturnal) bees.[12]
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.[14][15][16]
Methyl salicylate is also used as a bait for attracting male
orchid bees for study, which apparently gather the chemical to synthesize pheromones,[21] 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.[22] It has also been discovered that methyl salicylate works as a
kairomone that attracts some insects, such as the
spotted lanternfly.[23]
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,[24] in restoring (at least temporarily) the elastomeric properties of old rubber rollers, especially in printers,[25] as a transfer agent in printmaking (to release toner from photocopied images and apply them to other surfaces),[26] and as a penetrating oil to loosen rusted parts.
Safety and toxicity
Methyl salicylate is potentially deadly, especially for young children who may accidentally ingest preparations containing methyl salicylate such as an
essential oil solution. A single teaspoon (5 mL) of methyl salicylate contains approximately 6 g of salicylate,[27] which is equivalent to almost twenty 300 mg
aspirin tablets (5mL × 1.174g/mL = 5.87g). 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 140mg/kg of salicylates for a 10kg child (22lbs).[28] The lowest published lethal dose is 101 mg/kg body weight in adult humans,[29][30] (or 7.07 grams for a 70 kg adult). It has proven fatal to small children in doses as small as 4 mL.[17] 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 (using multiple patches against the manufacturer's instructions).[31]
Most instances of human toxicity due to methyl salicylate are a result of overapplication of topical analgesics, especially involving children. Salicylate, the major metabolite of methyl salicylate, may accumulate in
blood,
plasma or
serum which may help professionals to confirm a diagnosis of poisoning in hospitalized patients or to assist in an
autopsy.[32]
^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.
PMID15537163.
S2CID36124603.
^Knudsen, J. T.; Tollsten, L. (1993). "Trends in floral scent chemistry in pollination syndromes: floral scent composition in moth-pollinated taxa". Botanical Journal of the Linnean Society. 113 (3). Oxford Academic: 263–284.
doi:
10.1111/j.1095-8339.1993.tb00340.x.
^Cordeiro, G. D.; Fernandes dos Santos, I. G.; da Silva, C. I.; Schlindwein, C.; Alves-dos-Santos, I.; Dötterl, S. (2019). "Nocturnal floral scent profiles of Myrtaceae fruit crops". Phytochemistry. 162: 193–198.
doi:
10.1016/j.phytochem.2019.03.011.
PMID30939396.
S2CID92997657.
^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.
^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.
S2CID97484598.
^Baselt, R. (2008). Disposition of Toxic Drugs and Chemicals in Man (8th ed.). Foster City, CA: Biomedical Publications. pp. 1012–1014.
ISBN978-0-9626523-7-0.
^The British Pharmacopoeia Secretariat (2009).
"Index, BP 2009"(PDF). Archived from
the original(PDF) on 11 April 2009. Retrieved 5 July 2009.
^"NIHS Japan". Moldb.nihs.go.jp.
Archived from the original on 2013-02-17. Retrieved 2013-07-01.