Thymol, B.P. Thymol.
C10H13OH = 150.112.
Thymol (thyme camphor), or isopropyl-metacresol, C6H3CH3OHC3H7, is a crystalline phenol, obtained from the volatile oils of Thymus vulgaris, Linn. (N.O. Labiatae), Monarda punctata, Linn. (N.O. Labiatae), Carum copticum, Benth. and Hook. f. (N.O. Umbelliferae), and other plants. It is also official in the U.S.P. It may be isolated by distilling off the hydrocarbons present, then adding to the residue a solution of sodium hydroxide, with which the phenol combines to form a soluble phenate (thymol sodium), C6H3CH3C3H7ONa. The solution is allowed to clear, hydrochloric acid added to the clear liquid to liberate the thymol, which collects as an oily layer, and crystallisation induced in this, after separation and cooling, by the addition of a crystal of thymol. If the separated thymol is coloured, it may be treated with animal charcoal, and recrystallised from diluted alcohol. The oils from the plants mentioned above yield, in the order given, approximately 20 to 30 per cent., 60 per cent., and 45 to 55 per cent. of thymol. Thymol sometimes crystallises from old oils on cooling, but the method described ensures complete separation. Thymol can be prepared artificially from nitrocumic aldehyde, menthone, or paracymene. Thymol occurs in the form of large, colourless, transparent, rhombic prisms, having the characteristic, agreeable odour of thyme, and a spicy, burning, aromatic taste; it is not affected by light. The alcoholic solution is optically inactive, and should not be coloured by solution of ferric chloride. The aqueous solution becomes turbid on the addition of bromine water, but no crystalline precipitate is formed (phenol gives well-crystallised tribromophenol). Melting-point, 44° to 51°; boiling-point, 232°; specific gravity, 1.028. Solidifying point, 49° to 50°. On distillation with phosphorus pentasulphide it yields cymene. When rubbed with an equal weight of menthol, camphor, or phenol, liquefaction takes place. If a small crystal be dissolved in 1 mil of glacial acetic acid, the solution will assume a deep bluish-green colour on adding 3 decimils (0.3 milliliters) of sulphuric acid and 1/2 decimil (0.05 milliliters) of nitric acid. On heating 1 gramme of thymol with 5 mils of a 10 per cent. solution of sodium hydroxide in a test-tube by placing it in a water-bath, a clear, colourless, or very slightly reddish, solution is formed; the solution becomes darker on standing and, on adding a few drops of chloroform and shaking, a violet colouration is produced, but there should be no separation of oily drops (absence of laevo-pinene). On heating a small quantity (about 1 centigram) of thymol with 1 centigram of potassium hydroxide and 1 mil of chloroform, a purple-red colour is produced. The isomer carvacrol also gives this reaction, which appears to be characteristic of these two bodies. When a warm, slightly acid solution of mercuric nitrate is poured into an alcoholic solution of thymol, the mixture on cooling yields a magma of soft, felted needles of the double salt of mercury and thymol, which is colourless and odourless, but gradually becomes reddish and acquires a faint, thymol odour. A method for the determination of thymol is based upon the fact that, in alkaline solution, it combines with iodine, forming a red insoluble compound, and that the excess of iodine can be titrated back by means of standard thiosulphate after the solution has been acidified. Each molecule of thymol requires four atoms of iodine for precipitation.
Soluble in water (1 in 1500), alcohol (8 in 3), ether (8 in 3), chloroform (8 in 5), glycerin (1 in 190), petroleum spirit (1 in 6), turpentine oil (1 in 3), glacial acetic acid (4 in 3), solution of potassium hydroxide (1 in 6), in benzol, carbon bisulphide, fixed and volatile oils.
Action and Uses.—Thymol resembles phenol in its action, but owing to its insolubility in the fluids of the body it is absorbed much more slowly; it is also less irritant to wounds, while its germicidal action is greater than that of phenol, though less than that of naphthol. In alcoholic solution it penetrates the skin and produces local anaesthesia. It is used as an antiseptic lotion and mouth wash (1 in 1000), or as Liquor Thymolis Compositus; as a paint in ringworm (1 in 10 of alcohol, or alcohol and ether); and as an ointment (1 in 24 of soft paraffin, the thymol being dissolved with the aid of heat) in eczema, psoriasis, broken chilblains, parasitic skin affections, and burns. An ointment half this strength, perfumed with oil of lavender, is used to keep off gnats and mosquitoes. Thymol in oily solution (1 or 2 per cent.) is applied to the respiratory passages by means of a spray in nasal catarrh. An alcoholic solution may be inhaled from hot water or from a dry inhaler in laryngitis and bronchial affections. It is given internally in large doses, to robust adults, 2 grammes (30 grains) or more, repeated after two hours, to expel intestinal parasites, especially the miner's worm, Ankylostomum duodenale. To children and delicate persons not more than 6 decigrams (10 grains) should be given. For its action as a vermifuge it should be administered in a cachet or capsule; alcohol or other solvent of thymol should be avoided, and a purgative dose of castor oil administered a few hours subsequently. In large doses, it may cause symptoms of collapse and renal irritation, if time be allowed for absorption. Thymol is used to medicate absorbent gauze and wool for use as surgical dressings.
Dose.—3 to 12 centigrams (1/2 to 2 grains), or more.
- Glycerinum Thymolis Compositum, B.P.C.—COMPOUND GLYCERIN OF THYMOL. Syn.—Glycerinum Thymolis Alkalinum.
- Sodium bicarbonate, 1; borax, 2; sodium benzoate, 0.8; sodium salicylate, 0.52; menthol, 0.03; thymol, 0.05; eucalyptol, 0.13; oil of pine, 0.05; oil of wintergreen, 0.03; alcohol, 2.5; glycerin, 10; solution of carmine, 0.52; purified talc or kaolin, a sufficient quantity; distilled water, to 100. Used as an antiseptic and anticatarrhal wash. It is applied, diluted with 2 to 5 parts of water, as a spray solution to the throat and nose, or used as a nasal wash in a glass irrigator. A similar solution is used to cleanse the aural cavities and as a gargle and mouth wash.
- Liquor Antisepticus, U.S.P.—ANTISEPTIC SOLUTION.
- Similar to Liquor Thymolis Compositus, B.P.C., but with 25 of alcohol (95 per cent.).
- Liquor Thymolis Compositus, B.P.C.—COMPOUND SOLUTION OF THYMOL. Syn.—Liquor Antisepticus; Antiseptic Solution.
- Boric acid, 2.28; benzoic acid, 0.11; thymol, 0.11; eucalyptol, 0.03; spirit of peppermint, 0.5; spirit of gaultheria, 0.5; oil of thyme, 0.01; alcohol, 25; purified talc, or kaolin, a sufficient quantity; distilled water, to 100. Diluted with 3 or 4 parts of water, is used as an antiseptic mouth wash and gargle, to sniff up the nose in catarrh, and as a wash for wounds. It is taken internally as a mild antiseptic in flatulence and diarrhoea. Dose.—2 to 8 mils (1/2 to 2 fluid drachms).
- Pastillus Thymolis, B.P.C.—THYMOL PASTILLE. 1/32 grain.
- Solutio Thymolis (Volckmann).—VOLCKMANN'S SOLUTION OF THYMOL.
- Thymol, 0.1; glycerin, 2; alcohol, 2; water, sufficient to produce 100. This preparation is used as an antiseptic lotion, as a spray solution, and as an application for burns.
- Unguentum Thymolis Compositum, B.P.C.—COMPOUND THYMOL OINTMENT. Syn.—R.S.T. Ointment.
- Resorcin, 12.5; sublimed sulphur, 12.5; thymol, 12.5; hydrous wool fat, 18.75; lard, 45.75.
- Unguentum Thymolis Compositum Dilutum, B.P.C.—DILUTED COMPOUND THYMOL OINTMENT.
- Compound thymol ointment, 3; hydrous wool fat, 2; lard, 4.
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.