[468] A. Jurgens, Arch. Pharm. (3), xxiv. 127, 128.
The chemical tests are supplementary to the physiological; if the alkaloidal extract does not give the tingling, numbing sensation, aconitine cannot be present.
§ 426. Benzoyl-aconine (“isaconitine”), C31H43NO11, is obtained from aconitine by heating an aqueous solution of the sulphate or hydrochloride in a closed tube at 120°-130° for two or three hours, a molecule of acetic acid (9·27 per cent.) being split off, and benzoyl-aconine left.
It may be separated from the mixed alkaloids of the Aconitum napellus by dissolving in a 5 per cent. solution of hydrobromic acid (excess of acid being avoided), precipitating with a slight excess of ammonia, and shaking out with ether. The residue left after the ether is evaporated chiefly consists of aconitine; it is dissolved in just sufficient hydrobromic acid and the exactly neutral hydrobromate solution allowed to evaporate spontaneously in a desiccator; crystals of aconitine hydrobromide separate out, the mother liquor containing some benzoyl-aconine and “homonapelline.” The aqueous solution which has been exhausted with ether is now shaken out with chloroform. This chloroform solution contains most of the benzoyl-aconine, and on separation the residue is dissolved in just sufficient hydrochloric acid to form a neutral solution; this solution is concentrated on the water-bath with constant stirring, crystals of the hydrochloride form, and are filtered off from time to time and washed with a little cold water, the washings being added to the original liquid; the different fractions are mixed together, and the process repeated until they have a melting-point of 268°. Benzoyl-aconine is obtained from the hydrochloride by precipitating the aqueous solution by the addition of dilute ammonia, and extracting the solution with ether; the solution in ether is washed with water, dried by means of calcium chloride, and then distilled off. Benzoyl-aconine is left as a transparent colourless non-crystalline varnish of a melting-point near 125°.
The solution in water is alkaline to litmus. The base is readily soluble in alcohol, in chloroform, and in ether. The alcoholic solution is dextrorotatory. The solutions are bitter, but do not give the tingling sensation characteristic of aconitine. The hydrochloride, the hydrobromide, the hydriodide, and the nitrate have been obtained in a crystalline state. The most characteristic salt is, however, the aurochlor derivative. When aqueous solutions of benzoyl-aconine chloride and auric chloride are mixed, a yellow precipitate is thrown down, which (dissolved in alcohol, after being dried over calcium chloride, and slowly evaporated in a desiccator) deposits colourless crystals entirely different from the yellow crystals of aconitine gold chloride. These crystals have the composition C31H42(AuCl2)NO11, and therefore, by theory, should yield 22·6 per cent. of gold, and 8·2 per cent. of chlorine.
By hydrolysis benzoyl-aconine yields benzoic acid, which can be shaken out of an acid solution by ether and identified; one molecule of benzoic acid is formed from one molecule of benzoyl-aconine. Twenty per cent. of benzoic acid should, according to the formula, be obtained; Professor Dunstan found only 18·85 per cent.[469]
[469] Professor Dunstan found, as a means of two determinations, 21·6 per cent. of gold, and 7·8 per cent. of chlorine, which comes nearer his old formula of C33H44(AuCl2)NO12.—Journ. Chem. Soc., April 1893.