By distilling the resin of benzoin with ten times its weight of zinc dust, Ciamician (1878) chiefly obtained toluol, C₆H₅(CH₃).
Subjected to dry distillation, benzoin affords as chief product Benzoic Acid, C₇H₆O₂, together with empyreumatic products, among which Berthelot has proved the presence (in Siam benzoin) of Styrol ([p. 274]). The latter has been obtained in 1874 by Theegarten from Sumatra benzoë by distilling it with water. When the resin is fused with potash, it is partly decomposed and then, according to Hlasiwetz and Barth (1866), yields among other products, protocatechuic acid (more than 5 per cent.), C₆H₃(OH)₂COOH, para-oxybenzoic acid, C₆H₄(OH)COOH, and pyrocatechin, C₆H₄(OH)₂.
Benzoic acid exists ready-formed in the drug to the extent of 14 to 18 per cent.[1498] Although the acid dissolves in 12 parts of boiling water, the resin in which it is imbedded precludes its complete extraction by this means. It is however easily accomplished by the aid of an alkali, most advantageously by milk of lime, which does not combine with the amorphous resins.
Benzoin is not manifestly acted on by bisulphide of carbon, but if kept in contact with it for a month or two, very large colourless crystals of benzoic acid make their appearance. Brought into a warm room, the crystals quickly dissolve, but are easily reproduced by exposure to cold.
Most pharmacopœias require not the inodorous acid obtained by a wet process, but that afforded by sublimation, which contains a small amount of fragrant empyreumatic products. The resin, when repeatedly subjected to sublimation, affords as much as 14 per cent. of benzoic acid. It has long been known that the opaque white tears of benzoin are less rich in benzoic acid than the transparent brown resin in which they lie. From the latter, S. W. Brown (1833) extracted 13 per cent. of impure acid, but from the former scarcely 8½ per cent. We are by no means sure that such difference is constant.
Bitter almond oil, which by oxidation yields benzoic acid, is wanting in benzoin. Very little volatile oil is in fact to be got; half a pound of the best Penang benzoin yielded us by distillation with water only a few drops of an extremely fragrant oil (styrol?).
Ferric chloride imparts to an alcoholic solution of benzoin a dark brownish green, which is not acquired under the same circumstances by the aqueous decoction of the powdered resin. Benzoin dissolves in cold oil of vitriol, forming a solution of splendid carmine hue, from which water separates crystals of benzoic acid.
Kolbe and Lautemann in 1860 discovered in Siam and Penang benzoin together with benzoic acid, an acid of different constitution, which in 1861 they recognized as Cinnamic Acid, C₉H₉O₂. Aschoff (1861) found in a sample of Sumatra benzoin, cinnamic acid only, of which he got 11 per cent.; and in amygdaloid Siam and Penang benzoin only benzoic acid. In some samples of the latter, one of us (F.) has likewise met with cinnamic acid. On triturating this sort with peroxide of lead and boiling the mixture with water, the odour of bitter almond oil, due to the oxidation of cinnamic acid, is evolved.
The simultaneous occurrence of benzoic and cinnamic acids, or the absence of one or other of them in benzoin, is due to circumstances at present unexplained. Rump is of the opinion that the last named acid exclusively is present in the Penang (or Sumatra) benzoin and that no variety of the drug contains both those acids.
Rump (1878) treated Siam benzoic with caustic lime ([see p. 407]), precipitated the benzoic acid with hydrochloric acid, and agitated the liquid with ether. The latter on evaporating afforded a mixture of benzoic acid and Vanillin ([see article Vanilla]).