Methyl salicylate

Overview
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. Aside from its toxicity, methyl salicylate may be used by plants as a pheromone to warn other plants of pathogens such as tobacco mosaic virus. 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. 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.

Commercial production
Methyl salicylate can be produced by esterifiying 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. It is also used 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 can also be used as a transfer agent, to produce a manual copy of an image on a surface.

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.