This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Tonco (tonka or tonquin) beans are the seeds of two species of Dipteryx (N.O. Leguminosoe), viz. D. odorata, Willdenow, and D. oppositifolia, Willdenow, both trees of considerable size, the former a native of Guiana, the latter of Brazil.
The tree produces an indehiscent drupaceous fruit about the size of an egg, with a fibrous pericarp containing a single brownish violet seed, about the size and shape of an almond. The fallen fruits are collected, split open and the seeds removed and dried on flat rocks. Sometimes they are placed upon the market without further treatment, but large quantities are brought from South America to Trinidad, where they are prepared for the European and American markets. This preparation consists in steeping them in rum, removing the excess and drying the seeds. By this treatment a white crystalline crust (of coumarin) is produced on the surface of the seeds; the latter may therefore occur ' black' or ' frosted '; when dry they are packed in cases or casks for shipment.
Tonco beans closely resemble a Jordan almond in size and shape; they, are usually rather longer, varying from 3 to 4 cm. in length, and differ from the almond in having a nearly black, coarsely wrinkled surface which, in the frosted seeds, is covered with minute whitish crystals. The beans are rounded at one extremity but terminate at the other in a broad, flat point, just below which on the obtuse margin of the seed the micropyle may easily be discerned as a brownish scar. Internally they are dark yellow, yellowish brown, or nearly black, and consist of two large oily cotyledons, without endosperm, enclosing a plumule with two folded leaves and a short thick radicle. Tonco beans have a powerful and agreeably fragrant odour and an aromatic pungent taste.
The seeds owe their fragrance to coumarin, of which they may contain as much as 3 per cent.
Coumarin, coumaric or ortho-oxycinnamic anhydride, C6H4(CH)2OCO, forms colourless, fragrant crystals melting at 67°. It may be prepared synthetically by heating together salicylic anhydride, acetic anhydride, and anhydrous sodium acetate. It has been isolated from a variety of plants belonging not only to Leguminosoe, but several other natural orders, especially Gramineoe and Orchideoe. Cherry wood (Prunus Mahaleb, Linne), woodruff (Asperula odorata, Linne), and melilot (Melilotus officinalis, Desvaux) owe their pleasant aroma to coumarin.
Fig. 87. - Tonco bean. Fruit cut vertically, showing the seed. (Planchon and Collin).
The chief varieties of tonco beans are the Angostura and the Para, each of which may occur frosted or black; the Angostura beans are the larger and more valuable.