Santonin - Reactions and Properties

Reactions and Properties

Santonin can be converted to santonic acid (C₁₅H₂₀O₄) via based-catalyzed hydrolysis followed by a multistep rearrangement process.

Santonin dissolves in alkalies with formation of salts of this carboxylic acid. Santonin, in acetic acid solution, when exposed to sunlight for about a month, is converted into (colorless) photosantonic acid (C₁₅H₂₂O₅) which is generally regarded as less toxic. The ethyl ester of the latter is obtained when an alcoholic solution of santonin is exposed to sunlight (Sestini). A yellow coloration is developed upon exposure of santonin to light. Santonin is optically levorotatory.

Santonin is an organic chemical consisting of colorless flat prisms, turning slightly yellow from the action of light and soluble in alcohol, chloroform and boiling water. It is derived from santonica (the unexpanded flower-heads of Artemisia maritima var. stechmanniana). Others refer to A. cina or A. chamaemelifolia as being the derivative species.

According to the US Pharmacopoeia, santonin occurs "in colorless, shining, flattened, prismatic crystals, odorless and nearly tasteless when first put in the mouth, but afterward developing a bitter taste; not altered by exposure to air, but turning yellow on exposure to light. Nearly insoluble in cold water; soluble in 40 parts of alcohol at 15 °C. (59 °F.), in 250 parts of boiling water, and in 8 parts of boiling alcohol; also soluble in 140 parts of ether, in 4 parts of chloroform, and in solutions of caustic alkalies. When heated to 170 °C. (338 °F.), santonin melts, and forms, if rapidly cooled, an amorphous mass, which instantly crystallizes oil coming in contact with a minute quantity of one of its solvents. At a higher temperature, it sublimes partly unchanged, and, when ignited, it is consumed, leaving no residue. Santonin is neutral to litmus paper moistened with alcohol. Santonin yields, with an alcoholic solution of potassium hydrate, a bright pinkish-red liquid, which gradually becomes colorless. From its solution in caustic alkalies, santonin is completely precipitated by supersaturation with an acid".