By exhausting guaiacum resin with boiling bisulphide of carbon a slightly yellowish solution is obtained (containing chiefly guaiaretic acid?), which, on addition of concentrated sulphuric acid, turns beautifully red.
After the extraction of the guaiaconic acid there remains a substance insoluble in ether to which the name Guaiac Beta-resin has been applied. It dissolves in alcohol, acetic acid or alkalis, and is precipitated by ether, benzol, chloroform or carbon bisulphide in brown flocks, the composition of which appears not greatly to differ from that of guaiaconic acid.
Guaiacic Acid, C₁₂H₁₆O₆, obtained in 1841 by Thierry from guaiacum wood or from the resin, crystallizes in colourless needles. Hadelich was not able to obtain more than one part from 20,000 of guaiacum resin.
Hadelich’s Guaiac-yellow, the colouring matter of guaiacum resin, first observed by Pelletier, crystallizes in pale yellow quadratic octohedra, having a bitter taste. Like the other constituents of the resin, it is not a glucoside.
The decomposition-products of guaiacum are of peculiar interest. On subjecting the resin to dry distillation in an iron retort and rectifying the distillate, Guaiacene (Guajol of Völckel), C₅H₈O, passes over at 118° C. as a colourless neutral liquid having a burning aromatic taste.
At 205°-210° C., there pass over other products, Guaiacol, C₆H₄·OCH₃·OH, (methylic ether of pyrocatechin), and Kreosol C₆H₃·OH(CH₃)₂. Both are thickish, aromatic, colourless liquids, which become green by caustic alkalis, blue by alkaline earths, and are similar in their chemical relations to eugenic acid. Guaiacol has been prepared synthetically by Gorup-Besanez (1868) by combining iodide of methyl, CH₃I, with pyrocatechin, C₆H₄(OH)₂.
After the removal by distillation of the liquids just described, there sublime upon the further application of heat pearly crystals of Pyroguaiacin, C₃₈H₄₄O₆, an inodorous substance melting at 180° C. The same compound is obtained together with guaiacol by the dry distillation of guaiaretic acid. Pyroguaiacin is coloured green by ferric chloride, and blue by warm sulphuric acid. The similar reactions of the crude resin are probably due to this substance (Hlasiwetz).
Beautiful coloured reactions are likewise exhibited by two new acids which Hlasiwetz and Barth obtained (1864) in small quantity together with traces of fatty volatile acids, by melting purified resin of guaiacum with potassium hydrate. One of them is isomeric with pyrocatechuic acid.
Uses—Guaiacum resin is reputed diaphoretic and alterative. It is frequently prescribed in cases of gout and rheumatism.
Adulteration—The drug is sometimes imported in a very foul condition and largely contaminated with impurities arising from a careless method of collection.