SALICIN, SALICINUM, C13H18O7, the bitter principle of willow-bark, discovered by Leroux in 1831. It exists in most species of Salix and Populus, and has been obtained to the extent of 3 or 4% from the bark of S. helix and S. pentandra.
Salicin is prepared from a decoction of the bark by first precipitating the tannin by milk of lime, then evaporating the filtrate to a soft extract, and dissolving out the salicin by alcohol. As met with in commerce it is usually in the form of glossy white scales or needles. It is neutral, odourless, unaltered by exposure to the air, and has a bitter taste. It is soluble in about 30 parts of water and 80 parts of alcohol at the ordinary temperature, and in 0·7 of boiling water or in 2 parts of boiling alcohol, and more freely in alkaline liquids. It is also soluble in acetic acid without alteration, but is insoluble in chloroform and benzol. From phloridzin it is distinguished by its ammoniacal solution not becoming coloured when exposed to the air. Chemically, it is a glucoside derived from glucose and saligenin (o-oxy-benzyl alcohol), into which it is decomposed by the enzymes ptyaline and emulsin. Oxidation converts it into helicin (salicyl-aldehyde-glucose). Populin, a benzoyl salicin, is a glucoside found in the leaves and bark of Populus tremula.
Salicin is used in medicine for the same purposes as salicylic acid and the salicylates. It is also used as a bitter tonic, i.e. a gastric stimulant, in doses of five grains. The ordinary dose may go up to forty grains or more with perfect safety, though the British Pharmacopoeia limits it to twenty. The remote action of the drug is that of salicylic acid or the numerous compounds that contain it (see Salicylic Acid).