XII.—Colchicine.
§ 507. The whole of the Colchicum autumnale, or common meadow-saffron, is poisonous, owing to the presence of an alkaloid (discovered by Pelletier and Caventou) called Colchicine.
According to Johannson’s experiments, the dried colchicum seeds contain 1·15 per cent. of colchicine; the leaves, 1·459 per cent.; the bulbs, from 1·4 to 1·58 per cent.; and the roots, 0·634 per cent. The frequent poisoning of cattle in the autumn by colchicum, its use in quack pills for rheumatism, and its supposed occasional presence in beer, give it an analytical importance.
§ 508. Colchicine (C22H25NO6) may be extracted from the seeds, &c., in the manner recommended by Hübler:—The seeds are treated, without crushing, by hot 90 per cent. alcohol, and the alcoholic solution evaporated to a syrup, which is diluted with twenty times its bulk of water and filtered; the liquid is next treated with acetate of lead, again filtered, and the lead thrown out by phosphate of soda. Colchicine is now precipitated as a tannate.[548] The precipitation is best fractional, the first and last portions being rejected as containing impurities. The tannate is decomposed in the usual way with litharge and extracted by alcohol.
[548] The purest tannic acid must be used. The commercial tannin may be purified by evaporating to dryness with litharge, exhausting the tannate of lead repeatedly with boiling alcohol and water, and, lastly, suspending in water, and separating the lead by SH2.
A simpler method is, however, extraction by chloroform from an aqueous solution, feebly acidified, as recommended by Dragendorff. The parts of the plant are digested in very dilute acid water, and the resulting solution concentrated and shaken up with chloroform, which is best done in a separating tube.
Colchicine contains four methoxyl groups, and its constitutional formula is considered to be C15H9[NH(CH3CO)](COOCH3)(OCH3)3.
Its melting-point is 143°-147°. It is usually a white, gummy mass. It is easily soluble in cold water, in alcohol, and in chloroform. The solutions are lævorotatory. It is hardly soluble in ether. Boiling with dilute acids or alkalies in closed tubes yields colchiceine.