2.2.3 Salicin
Synonyms Salicoside; Salicyl alcohol glucoside; Saligenin β-D-glucopyranoside.
Biological Source It is obtained from the bark of poplar (Populus) and willow (Salix) and also found in the leaves and female flowers of the willow. It is specifically found in two species of Salix, namely: Salix fragilis and Salix purpurea , belonging to the family Salicaceae. It is also found in the root bark of Viburnum prunifolium L., family : Caprifoliacea and in Spiraea ulmaria, family: Rosaceae.
Geographical Source It grows in China, Europe and in India.
Preparation The powdered bark is macerated with hot water for several hours whereby the glucoside (salicin) and tannin are extracted collectively. The resulting liquid extract is filtered, concentrated under vacuum and treated with lead acetate to remove the tannins as a precipitate. It is subsequently treated with hydrogen sulphite to remove the excess of lead. The clear filtrate is neutralized with ammonia, allowed to concentrate, chilled to obtain the crystals of salicin. The crude salicin may be further purified by treating its solution with animal charcoal and concentrating followed by cooling.
Description It occurs as colourless crystals or prisms or scales. It has a very bitter taste. It is highly soluble in hot water and practically insoluble in ether. It is a levoratatory substance [ (α)D:–63°].
Chemical Constituents It is hydrolysed in the presence of the enzyme emulsin by yielding one mole each of saligenin (aglycone) and D-glucose as stated below:
When hydrolysis is done in an acidic medium by boiling for a prolonged duration, two moles of saligenin combine together to provide saliretin (water insoluble) with the loss of a mole of water, which may be summarised as shown under:
Chemical Tests
1. It gives an instant bright red colour with concentrated sulphuric acid that fades out on the addition of water.
2. Its hydrolysed product saligenin gives a blue colour with ferric chloride.
3. On oxidation with potassium dichromate and sulphuric acid and heating yields salicylaldehyde having a characteristic odour.
4. It gives specific colours with the following reagents:
Frachde’s Reagent : Violet colour
Mandelin’s Reagent* : Purple red colour
Erdmann’s Reagent** : Bright red colour
Uses
1. It is used as an analgesic
2. It has been employed as a bitter stomachic.
3. It is also used as an antirheumatic agent.
4. It is used as a standard substrate in evaluating enzymes preparations containing β-glycosidase.
