COUMARIN, an odorous substance which occurs in sweet woodruff (Asperula odorata), in the tonka bean and in yellow melilot (Melilotus oficinalis) ; it can be obtained from the tonka bean by extraction with alcohol. Coumarin, is prepared artificially by the action of acetic anhydride and sodium acetate on salicyl aldehyde (W. H. Perkin, Sr. 1875). It can also be pre pared by heating a mixture of phenol and malic acid with sulphuric acid. It forms rhombic crystals (from ether) melting at 67° C and boiling at 29o° C, which are readily soluble in alcohol, and moderately soluble in hot water. It is applied in perfumery for the preparation of the Asperula essence. On boiling with concen trated caustic potash coumarin yields the potassium salt of ortho coumaric acid. Sodium amalgam reduces it, in aqueous solution, to melilotic acid. It forms addition products with bromine and hydrobromic acid ; it yields also oxonium salts : platinichloride, aurichloride, hydriodide-periodide and cobalticyanide. By the action of phosphorus pentasulphide it is converted into thiocou marin, which melts at I °I ° C.
Ortho-coumaric acid (o-hydroxycinnamic acid) melts at 208° C and is easily soluble in hot water and in alcohol. It cannot be converted into coumarin by heating alone, but it is readily trans formed on heating with acetic anhydride or acetyl chloride. By the action of sodium amalgam it is readily converted into melilotic acid, which melts at 81° C, and on distillation furnishes its lactone, hydrocoumarin, melting at 25° C. The homologues of coumarin may be obtained by the action of sulphuric acid on phenol and the higher fatty acids (propionic, butyric and isovaleric anhy drides), substitution taking place at the carbon atom in the a position to the —CO— group, whilst by the condensation of acetoacetic ester (q.v.) and phenols with sulphuric acid the substituted coumarins are obtained.
Umbelliferone or 7-hydroxycoumarin, occurs in the bark of Daphne mezereum and may be obtained by distilling such resins as galbanum or asafoetida. It may be synthesized from f-resor cylaldehyde, acetic anhydride and sodium acetate. Daphnetin and aesculetin are dihydroxycoumarins.
The structural formulae of coumarin and the related substances are :