C. Methyl Salicylate
Synonyms Winter green oil; Betula oil; Sweet birch oil; Teabery oil.
Chemical Structure 2-Hydroxybenzoic acid methyl ester; (C8H8O3)
Occurrence It is largely found in a variety of medicinal plants, namely: Flowers of Acacia farnesiana (L.) Willd. (Family: Fabaceae)-Cassie, Huisache; Cananga odorata (Lam.) Hook. f. & Thoms (Family: Annonaceae)-Cananga, Ylang-Ylang; Leaves of Chenopodium ambrosioides L. (Family: Chenopodiaceae)-Wormseed; Erythroxylum coca Lam. (Family: Erythroxylaceae)-Coca; Flowerbuds of Filipendula ulmaria (L.) Maxim (Family: Rosaceae)-Meadowsweet, Queen of the Meadow; Twigs of Gaultheria procumbens L. (Family: Ericaceae)-Wintergreen, Teaberry, Boxberry; Bark of Betula lenta L. (Family: Betulaceae)-Sweet Birch. However, oil of wintergreen contains upto 99% methyl salicylate. It is pertinent to mention here that in several aromatic medicinal plants, for instance: Wintergreen, the active chemical constituent i.e., methyl salicylate does not occur as such, but is present in the form of a glucoside known as Gaultherin which upon enzymatic hydrolysis gives methyl salicylate and primeverose (glucoxylose) as shown under:
Isolation Methyl salicylate may be obtained from gaultherin by enzymatic hydrolysis and then subjecting the resulting products of reaction to very low temperature when the former gets solidified at – 8.6°C and hence may be separated easily.
Characteristic Features It is a colourless, yellowish or reddish, oily liquid. Its odour and taste resembles to that of gaultheria. Its physical parameters are: mp – 8.6°C; bp 220-224°C; d2525 1.184; d of the natural ester is ~ 1.180; and n20D 1.535-1.538. It is very sparingly soluble in water (1 g in 1500 ml), but freely soluble in chloroform and ether. It is, however, miscible with alcohol and glacial acetic acid.
Identifications
1. It develops a red-violet colouration on being treated with cold saturated aqueous solution of FeCl3, that lasts for about 15 minutes.
2. Methyl salicylate readily forms a soluble ester-salt with a moderately concentrated aqueous solution of KOH as potassium methyl salicylate.
3. Upon saponification the ester yields salicylic acid (mp 158°C) and methanol respectively.
4. Methyl salicylate may also be identified by the formation of several derivatives as stated below:
(i) Methylo-acetoxy benzoate (mp 52-52.5°C)—with Acetic Anhydride,
(ii) Methyl-o-benzoxy benzoate (mp 92°C)—with Benzoyl Chloride,
(iii) o-Cabomethoxyphenyl-N-phenyl urethane—with Phenylisocyanate.
Uses
1. Methyl salicylate has local irritant, antirheumatic and antiseptic properties. It is an important ingredient of Iodex(R) ointment for relief of pain in several conditions like, pulled muscle, muscular pain, pain in joints, etc.
2. It also finds its extensive usage in a variety of products, such as: flavouring of food products, beverages, candies, confectionery, toothpastes, mouth washes, gargles, and pharmaceutical preparations.
3. It is also used in perfumery.
