Methylis Salicylas. Methyl Salicylate.

Related entry: Oil of Gaultheria - Birch Tar Oil - Oil of Betula - Salicylic acid - Acetyl-salicylic acid

C₈H₈O₃ = 152.064.
Synonym.—Artificial Oil of Wintergreen or Sweet Birch.

Methyl salicylate, C₆H₄(OH)COOCH₃, is the methyl ester of salicylic acid, and the principal constituent of oil of wintergreen and oil of sweet birch, existing in the former to the extent of about 99 per cent., and in the latter to about 99.8 per cent. It is official in the U.S.P. Much of the oil of wintergreen of commerce, however, is the synthetic methyl salicylate, which is practically identical with the natural products. It may be prepared by dissolving 14 of salicylic acid in 60 of methyl alcohol, then gradually adding 30 of sulphuric acid, warming for about twenty-four hours, and distilling in a current of steam. The distillate is subsequently washed and separated. Methyl salicylate occurs as a colourless, or pale yellow, oily liquid with the strong, characteristic odour and aromatic, sweetish taste of wintergreen. Specific gravity, 1.183 to 1.188; boiling-point, 219° to 221°. Optically inactive. The aqueous solution is neutral or slightly acid to litmus, and yields with a trace of ferric chloride an intense violet colouration. It should form a perfectly clear solution with 5 parts of alcohol (70 per cent.) at 20°. On distillation in a flask it should yield no fraction containing alcohol or chloroform. On adding 10 mils of solution of potassium hydroxide (5 per cent.) to 1 mil of the methyl salicylate in a large test-tube, and shaking, a clear, colourless, or faintly yellow solution should result, without separation of oily drops on the surface or at the bottom of the liquid (absence of volatile oils or of petroleum). The alkaline liquid, on dilution with three volumes of water and the addition of slight excess of hydrochloric acid, yields a white crystalline precipitate of salicylic acid, which, on washing and drying, should respond to the tests for the purified substance (absence of methyl benzoate, etc.).

Slightly soluble in water, soluble in all proportions of alcohol, ether, chloroform, glacial acetic acid, or carbon bisulphide.

Action and Uses.—Methyl salicylate is rapidly absorbed when rubbed on the skin, and this property allows the concentration of its action upon rheumatic and stiff joints and in lumbago; it may also be applied to the forearm or any convenient surface for the general action of the salicylates in acute and chronic rheumatism, pharyngitis and chorea, etc. (see Sodii Salicylas). In acute lumbago, massage with methyl salicylate acts almost immediately; and it has been shown that, in the most inveterate cases of stiff back, with the presence of rheumatic nodules, such massage, applied at intervals for a month or two if necessary, will generally remove the condition. The pure substance may be painted on the skin and covered with oiled silk or gutta percha tissue, or it may be mixed with an equal quantity of olive oil and applied with gentle friction or on lint. Methyl salicylate should be used for application to the skin rather than natural oil of wintergreen, as the latter frequently causes irritation and may give rise to a rubeoliform eruption. It is recommended for local application in orchitis and mumps. An ointment of methyl salicylate with hydrous wool fat (1 in 8) is prepared for use in rheumatism and neuralgia, menthol (1 in 16) being sometimes added. Methyl salicylate is administered in acute and chronic rheumatism enclosed in a gelatin capsule (5 or 10 minims in each). It may be emulsified with mucilage of gum acacia and given in mixture form, but its taste is pungent and objectionable. It is used as a flavouring agent, and as an antiseptic in mouth washes, tooth pastes, and powders. Mesotan, salicylic-methoxy-methylester, is an odourless liquid, used as a substitute for methyl salicylate. It is soluble in alcohol and decomposed by water. Mixed with an equal quantity of olive oil, it is known as Mesotanol and is applied for rheumatism. Spirosal, the mono-glycol ester of salicylic acid, is a colourless and odourless liquid soluble in alcohol or olive oil. It is applied in lumbago and rheumatism diluted with 3 parts of alcohol or olive oil.

Dose.—½ to 1 mil (8 to 15 minims).

PREPARATIONS.

Linimentum Methylis Salicylatis, B.P.C.—METHYL SALICYLATE LINIMENT. Syn.—Linimentum Betulae Compositum; Compound Liniment of Birch.

Menthol, 5; oil of eucalyptus, 10; essential oil of camphor, 25; methyl salicylate, to 100. This liniment is miscible with either spirit or oil, and is used to paint over rheumatic joints or neuralgic areas, the parts being covered subsequently with flannel or gutta-percha tissue. It has been found of great value in the treatment of lumbago and sciatica.

Linimentum Methylis Salicylatis Compositum, B.P.C.—COMPOUND LINIMENT OF METHYL SALICYLATE.

Menthol, 5; chloral hydrate, 5; extract of Indian hemp, 0.5; essential oil of camphor, 25; methyl salicylate, to 100.

Pasta Methylis Salicylatis Composita, B.P.C.—COMPOUND METHYL SALICYLATE PASTE. Syn.—Pasta Analgesica; Analgesic Paste. 1 in 2.

This preparation is put up in collapsible tubes.

Unguentum Methylis Salicylatis, B.P.C.—METHYL SALICYLATE OINTMENT. 1 in 2.

Applied with friction over rheumatic joints.

Unguentum Methylis Salicylatis Compositum, B.P.C.—COMPOUND METHYL SALICYLATE OINTMENT. Syn.—Unguentum Betulae Compositum; Unguentum Analgesicum; Analgesic Balsam. 1 in 2.

Used both for its analgesic and curative properties in sciatica, lumbago, and rheumatism.

Unguentum Methylis Salicylatis Compositum Dilutum, B.P.C.—DILUTED COMPOUND METHYL SALICYLATE. OINTMENT.

Compound methyl salicylate ointment, 25; lanolin ointment, 75.

Unguentum Methylis Salicylatis Dilutum, B.P.C.—DILUTED METHYL SALICYLATE OINTMENT.

Methyl salicylate ointment, 25; lanolin ointment; 75.

The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.