Methyl salicylate

Methyl salicylate (chemical formula C₆H₄(HO)COOCH₃; also known as salicylic acid methyl ester, oil of wintergreen, betula oil, methyl-2-hydroxybenzoate) is a natural product of many species of plants. Some of the plants producing 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 infested with herbivorous insects, the release of methyl salicylate may function as an aid in the recruitment of beneficial insects to kill the herbivorous insects. 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. 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.
• Some species of the genus Betula in the family Betulaceae, particularly those in the subgenus Betulenta.
• All species of the family Spiraea, 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 Sweet Birch (Betula lenta) and Eastern Teaberry (Gaultheria procumbens).

Uses

It is used as a rubefacient in deep heating liniments, and in small amounts as a flavoring agent at no more than 0.04%. 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.

It is one of many compounds that is attractive to males of various species of orchid bees, who apparently gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study.

Methyl salicylate also 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 is used in some kinds of chewing gum and candy, as an alternative to the more common peppermint and spearmint oils. 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 ground. This effect can be observed by crushing wintergreen Life Savers candy in a dark room.

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

Methyl salicylate is also an active ingredient in Ben Gay muscle rub and similar products for relief of minor aches and pains associated with backaches, arthritis, strains, bruises, and sprains.

Methyl salicylate is added in small amount in glacial acetic acid while travelling in cold countries to decrease the freezing point of glacial acetic acid.

Safety

In pure form, methyl salicylate is toxic, especially when taken internally. The lowest published lethal dose is 101 mg/kg body weight in adult humans. It has proven fatal to small children in doses as small as 4 mL. A 17 year-old cross-country runner at Notre Dame Academy on Staten Island, died April 3, 2007, after her body absorbed high levels of methyl salicylate through excessive use of topical muscle-pain relief products.

See also

• Salicylic acid
• Wintergreen

References

External links

Toxicity:

• MedlinePlus - Methyl salicylate overdose
• MedlinePlus - Sports cream overdose
• CNN - Medical examiner: Sports cream caused teen's death
• NLM Hazardous Substances Databank – Methyl salicylate