Tonco Semina. Tonco Seeds. Coumarinum. Coumarin.
Synonyms.—Tonka Beans; Tonquin Beans.
Tonco seeds are the product of Dipteryx odorata, Willd. (N.O. Leguminosae), and D. oppositifolia, Willd., the former indigenous to Guiana, the latter to Brazil. The trees produce fruits about the size of a large egg, the seeds being imbedded in a pulp which is surrounded by a hard fibrous shell. The seeds are separated and dried. They are often "frosted" by steeping them in rum, and then spreading them out to dry. The seeds are usually 3 to 4 centimetres in length, and resemble Jordan almonds in shape. The surface is nearly black, much wrinkled, and, in the case of frosted beans, covered with minute, whitish crystals of coumarin. Each seed contains two yellowish-brown, oily cotyledons. The odour is fragrant; taste, aromatic and bitter.
Constituents.—The chief constituent of tonco seeds is coumarin, of which they may contain as much as 3 per cent.; while the fixed oil in the cotyledons may amount to 25 per cent.
Uses.—Tonco seeds were formerly used as the source of coumarin, but the greater part of this substance employed is now produced synthetically (see Coumarinum).
C9H6O2 = 146.048.
Synonyms.—Cumarin; Ortho-oxycinnamic Anhydride; Cumaric Anhydride.
Coumarin, C6H4(CH)2OCO, the δ-lactone of coumaric acid, is the odorous principle of the Tonka or Tonquin bean, Dipteryx odorata, Willd., and D. oppositifolia, Willd. (N.O. Leguminosae); it is also found in woodruff and many other plants, and is prepared commercially from deer-tongue leaves. It may be obtained from the coarsely powdered material by boiling with 80 per cent. alcohol, concentrating, and mixing the strong liquid with four times its volume of boiling water; the solution is filtered through a damp filter-paper to remove fat, and then set aside to cool, when the coumarin crystallises out, and may be purified by re-dissolving in hot water, decolourising with animal charcoal, and again crystallising. It may be prepared synthetically by mixing 3 of salicylic aldehyde, 5 of acetic anhydride, and 4 of anhydrous sodium acetate, gently boiling for several hours in a reflux condenser, cooling, and adding water to the crystalline mass obtained; the oily liquid which separates is distilled, and the coumarin obtained is dissolved in hot water and crystallised. It occurs in the form of colourless prismatic crystals, having a characteristic, persistent, fragrant odour, and a bitter, aromatic taste. Melting-point, 67°. It sublimes at the heat of a water-bath without decomposition, and leaves no residue on ignition. It dissolves in concentrated sulphuric acid in the cold without colouration, and is scarcely coloured on warming. In cold solution of sodium hydroxide it dissolves with difficulty; on warming, it dissolves with a slight green colouration, and from this solution excess of hydrochloric acid throws out coumarin in colourless needles. Acetanilide, which is used as an adulterant, may be detected by boiling 1 centigram of the sample with 1 mil of 25 per cent. hydrochloric acid, adding 2 mils of a 5 per cent. phenol solution, and then a little freshly prepared chlorinated lime solution; if acetanilide was present a red colour will appear, which, on addition of solution of ammonia in excess, changes to indigo blue.
Soluble in water (1 in 400), and boiling water (1 in 50); also readily soluble in alcohol, ether, chloroform, fixed oils, and volatile oils.
Action and Uses.—Coumarin has a powerful anaesthetic action and has been recommended for use in laboratory experiments on animals, as it has little effect upon the circulation. It readily excites vomiting in man, which renders it unsuitable as a hypnotic. Coumarin is used in perfumery, not only on account of its own fragrance, but for its property of fixing other odours. It is employed in pharmacy to disguise disagreeable odours, especially that of iodoform, for which purpose 1 part of coumarin is used to 50 parts of iodoform. When applied directly to the mucous membrane, coumarin is extremely irritant, and after prolonged use gives rise to an eczematic eruption; in powdering large quantities the dust should not be inhaled.