C13H18O7 = 286.144
Salicin, C6H11O5.C6H4CH2OH, is a crystalline glucoside, obtained from the bark of various species of Salix and of Populus;a large quantity is obtained from the bark of Salix fragilis, Linn., and from the bark of S. purpurea, Linn. It is also official in the U.S.P. It may be extracted by treating a strong decoction of the bark with lead oxide, then adding sulphuric acid and barium sulphide, filtering, evaporating to a syrupy consistence, and setting the liquid aside for a time; on standing the salicin crystallises out, and may be purified by recrystallisation. Salicin occurs in odourless, very bitter, colourless, shining, trimetric, tabular crystals, or as a white, crystalline powder. Melting-point, 201°. Its aqueous solution is neutral to litmus and is laevogyrate. Heated in a test-tube until it turns brown, a few mils of water added, and then a drop of solution of ferric chloride, a violet colour is produced, due to the formation of saligenin. When warmed with diluted acids salicin is hydrolysed to saligenin (salicyl alcohol) and dextrose. Boiled with diluted hydrochloric or sulphuric acid it is hydrolysed, yielding saliretin and dextrose. Emulsin hydrolyses the glucoside to saligenin and dextrose, Salicin is not precipitated from an aqueous solution by tannic acid or potassio-mercuric iodide (distinction from alkaloids). No residue should remain on ignition (absence of mineral matter).
Soluble in water (1 in 28), alcohol (1 in 60); insoluble in ether.
Action and Uses.—Salicin is partially decomposed in the stomach and intestines; it is converted into salicyl alcohol, and this is subsequently oxidised in the body into salicylic acid. The glucoside is less irritant to the mucous membranes than the salicylates, and is less certain in its action. It is in part excreted unchanged in the urine, and partly as salicyl alcohol, salicylic acid, and salicyluric acid. The action of salicin is virtually that of salicylic acid. Given in solution, it is a bitter, increasing the flow of saliva and improving the appetite. It is used as a specific in acute rheumatism, for which purpose it is less depressing than salicylic acid, and its action is more prolonged. It is also employed in influenza, ague, and malarial fevers. Salicin has been used successfully in some chronic skin diseases, especially in cases of lupus erythematosus and psoriasis. It is best administered in solution in mixture form, but it may also be given in cachets, or in pills massed with glycerin of tragacanth, or in the form of Granulae Salicini. The bitter taste of salicin is well covered by liquid extract of liquorice.
Dose.—3 to 12 decigrams (5 to 20 grains).
- Granulae Salicini, B.P.C.—GRANULAR EFFERVESCENT SALICIN. 1 in 12 1/2.
- Dose.—4 to 8 grammes (60 to 120 grains).
- Tablettae Salicini, B.P.C.—SALICIN TABLETS. 5 grains.
- Dose.—1 to 4 tablets.
Willow bark is obtained from Salix alba, Linn. (N.O. Salicineae), and other species of Salix, trees indigenous to Central and Southern Europe. The bark is generally met with in commerce in thin, channelled pieces about 1 to 2 centimetres wide, the outer surface is smooth or slightly longitudinally wrinkled (in older barks rugged), the inner, striated, fibrous, and pale reddish in colour. The transverse section exhibits under the lens numerous minute, tangentially arranged groups of bast fibres, and under the microscope a thin cork consisting of two or three rows of cells with strongly thickened outer walls. Odour, slight; taste astringent and slightly bitter. Commercial willow bark, although generally referred to S. alba, is often the bark of some other species, as indicated by its anatomical characters. Salicin is usually prepared from the bark of S. fragilis, Linn., which is largely grown in Belgium, and yields the bark known as "rood scorce," which contains about 3 per cent. of salicin.
Constituents.—Commercial willow bark contains tannin (up to 13 per cent.) as its chief constituent; it also contains salicin, but usually in small proportion only.
Action and Uses.—Willow bark is employed as a bitter and astringent.
SALICIS NIGRAE CORTEX.
BLACK WILLOW BARK.
Synonym.—Pussy Willow Bark.
Black willow bark is obtained from the black willow, Salix discolor, Muhl. (N.O. Salicineae), a tree 15 to 25 feet high, common in the States of North America. The bark occurs in long, thin, tough, fibrous strips, covered externally with a thin, brownish or greenish-brown, wrinkled cork; the inner surface is pale reddish-brown in colour. It has a bitter, astringent, and somewhat aromatic taste. The bark of Salix nigra, Marsh., is darker, thicker, and less bitter than that of S. discolor.
Constituents.—This variety of willow bark contains from 3.3 to 4.3 per cent. of tannin and about 1 per cent. of salinigrin, a white crystalline glucoside, soluble in water (1 in 52), and in alcohol (1 in 218); melting-point, 195°; rotation, -87.3°; on hydrolysis it yields glucose and m-oxybenzaldehyde; it may readily be distinguished from salicin by yielding a colourless solution with sulphuric acid, salicin under these conditions producing a blood-red colour.
Action and Uses.—Black willow bark has been prescribed in gonorrhoea, and to relieve ovarian pain. A liquid extract is prepared and is used in mixture form with other sedatives.
- Extractum Salicis Nigrae Liquidum, B.P.C.—LIQUID EXTRACT OF BLACK WILLOW. 1 in 1.
- Dose.—1 to 4 mils (15 to 60 minims)
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.