2.3.1 Coumarins
The chemistry of coumarin may be understood more vividly with the help of geometrical isomers of o-hydroxycinnamic acids, one of which instantly yields the lactone coumarin (or benzopyran), whereas the other fails to do so. Therefore, the former is the cis-isomer called coumarinic acid, and the latter the trans-isomer known as the coumaric acid as given below:
Coumarin
Synonyms cis-o-Coumarinic acid lactone; Cumarin; Coumarinic anhydride; Tonka bean comphor.
Biological Sources Coumarin is present in a large number of medicinal herbs, such as:
Acacia farnesiana (L.) Willd (Fabaceae)-Cassie, Huisache; Apium graveolens L. (Apiceae)-Celery; Artemisia dracunculus L. (Asteraceae)-Tarragon; Chamaemelum nobile (L.) All. (Asteraceae)-Roman Camomile, English Camomile, Camomile; Cinnamomum verum J.S. Presler (Lauraceae)-Ceylon Cinnamon; Dipteryx odorata (Aubl.) Willd (Fabaceae)-Tonka Bean, Tonga, Cumaru; Hyoseyamus niger L. (Solanaceae)-Henbane, Henblain, Jusquaime; Myroxylon balsamum var. Pereirae (Royle) Harms. (Fabaceae)-Balsam of Peru; Peumus boldus Molina (Monimiaceae)-Boldo; Pimpinella anisum L. (Apiaceae)-Anise; and Trilisa odoratissima (J.F.Gemel.) Cass (Asteraceae)-Deertongue, Deer's Tongue.
Characteristic Features Coumarin crystals have an orthorhombic and rectangular plates. They have a pleasant, fragrant odour resembling to that of the vanilla beans and a burning taste. The physical characteristics are, namely: mp 68-70°C and bp 297-299°C. Its solubility in water is very poor, viz., 1g dissolves in m 400 ml of cold and 50 ml of boiling water. However, it is freely soluble in ethanol, chloroform, ether, oils and also in alkaline solutions of NaOH or KOH.
Uses It is used extensively as a flavouring agent in pharmaceutical formulations.
