Source, Etc

Araroba, or, as it is often termed, Goa powder, is a substance found in cavities in the trunk of Andira Arardba, Aguiar (N.O. Leguminosoe), a large tree common in the damp forests of Bahia (Brazil).

This remarkable substance is found filling longitudinal fissures in the trunk of the tree. From careful microscopical examinations that have been made of the fragments of wood picked from the crude drug, it would appear that the walls of both parenchymatous and prosenchymatous cells, as well as those of the vessels, undergo a complete change, by which they are converted into a yellowish, powdery, substance, araroba. This change is observable first in the secondary thickenings of the cell-wall, but afterwards the cell-walls themselves break-down, thus forming cavities of considerable size which are filled with the araroba. The exact nature of the change of the influences that induce it, and the manner in which it is effected, is unknown; it appears to be a pathological not a normal physiological process.

Araroba is collected by felling the tree, sawing the trunk into lengths, and splitting these longitudinally. The yellowish powder is then scraped out with the axe, by which means numerous splinters of wood and other debris are simultaneously removed. It is exported in that crude condition, and may be purified by sifting it as free as possible from fragments of wood, drying, and powdering it. The drug appears to have been long known to the natives of Brazil as a cure for certain skin diseases. In 1864 Kemp drew attention to the Goa powder that was used in India for similar purposes, and this was proved in 1875 to be identical with the araroba of the Brazilians.

Description

The crude drug, as imported, consists of a brownish yellow or umber-brown powder mixed with numerous small and large fragments of wood. Microscopical examination of the powder shows the presence of numerous minute prismatic crystals, and granular, amorphous matter accompanied by vegetable debris. The smoothed transverse surfaces of the larger fragments of wood show thin, yellow, medullary rays, vessels, and here and there yellow masses (of araroba). As already observed, it is sometimes purified by simply freeing it from the debris present, drying and powdering; but the purification is more generally effected by grinding the crude drug, drying it, boiling it with benzene, and filtering; the. hot benzene solution deposits on cooling a yellow, crystalline powder which forms the chrysarobin of commerce. This is a yellow, crystalline, tasteless, and inodorous powder, soluble in hot chloroform and benzene, almost entirely soluble in hot alcohol, very sparingly and incompletely soluble in petroleum spirit, and practically insoluble in water. Hot solution of potash dissolves it almost entirely. To solution of ammonia it imparts at first a slight pink tinge; this colour, however, quickly deepens owing to oxidation of the chrysarobin (which is insoluble in ammonia) to chrysophanic acid (which is soluble).

Fig. 241.   Araroba. Portion of a transverse section of the wood of Andira Araroba, near to a cavity filled with araroba. S, vessels; l, wood fibres; p,wood parenchyma; m, medullary rays. Nearly all the elements contain a dark substance, which in the upper part forms a dense mass, x (omitted from the illustration). Magnified. (Vogl.)

Fig. 241. - Araroba. Portion of a transverse section of the wood of Andira Araroba, near to a cavity filled with araroba. S, vessels; l, wood fibres; p,wood parenchyma; m, medullary rays. Nearly all the elements contain a dark substance, which in the upper part forms a dense mass, x (omitted from the illustration). Magnified. (Vogl).

Purified araroba melts when heated, gives off yellow fumes, and finally burns, leaving not more than 1 per cent, of ash.

Crude araroba, as imported, often contains from 15 to 30 per cent, of water, which appears to be added to prevent the irritating dust from rising; it may yield from 50 to 75 per cent, of purified araroba.

Constituents

Purified araroba varies considerably both in the constituents present and the proportion in which they occur. The following table may suffice to indicate its approximate composition (Tutin and Clewer, 1913): -

Chrysophanol (chrysophanic acid)

47

to

6.7

per cent.

Emodin monomethyl ether . . . about

1.6

to

2.2

,,

Chrysophanolanthranol ('chrysarobin') about

26.0

to

620

,,

Anthranol of emodin monomethyl ether

Small amount

Monomethyl ether of dehydroemodin-anthranol ...

13.4

to

411

per cent.

Ararobinol ... . about 4

,,

Emodin

trace

Inseparable mixture of substances and amorphous matter .. about

12.0

to

300

per cent.

Chrysophanolanthranol, often called chrysarobin, C15H12O3, crystallises in yellow leaflets melting at 199°. It is insoluble in aqueous ammonia, but is converted by oxidation into chrysophanol which is soluble.

Chrysophanol (chrysophanic acid), C15H10O4, crystallises in deep orange-coloured leaflets melting at 191°.

Monomethyl ether of dehydroemodinanthranol, C16H12O4, crystallises in pale yellow needles melting at 265°.

Ararobinol, C23H16O5, crystallises in yellow crystals without definite melting point.

There is no definite knowledge as to which constituent or constituents its medicinal value is to be attributed.

Uses

Purified araroba has been used successfully in ringworm, psoriasis, and other skin diseases; it acts apparently by destroying low vegetable organisms.