C8H17N = 127.46.
Synonyms.—Conine; Conicine; Cicutine.
Coniine, or α-propyl - piperidine, C5H9(C3H7)NH, is a liquid alkaloid found in all parts of the hemlock, Conium maculatum, but more especially in the immature fruit, in combination with malic acid. It may be obtained by distilling the crushed seeds with weak solution of potassium hydroxide over a steam-bath, neutralising the distillate obtained with hydrochloric acid, evaporating the solution to dryness, adding excess of potassium hydroxide to the alkaloidal salt, extracting the base thus liberated with ether, and finally purifying by distillation in a current of hydrogen. By the action of sodium on an alcoholic solution of allyl-pyridine, which is a liquid product of the action of paraldehyde on picoline, coniine may be prepared synthetically. Coniine occurs in the form of an almost colourless liquid with a penetrating mouse-like odour and an acrid taste; it is volatile and dextrorotatory, and becomes brown on exposure to the air. The aqueous solution has an alkaline reaction. The base takes up 25 per cent. of water, and the cold saturated solution becomes turbid on warming. Specific gravity, 0.890. Boiling-point 166°. On cooling, it congeals to a crystalline mass, which melts at -2°. It is a powerful base, and unites with acids to form stable crystalline salts. With concentrated sulphuric acid it gives first a blood-red, and then green, colour. Potassium cadmium iodide yields an amorphous precipitate, thus distinguishing it from nicotine, which yields a crystalline precipitate. Solution of coniine is not precipitated by platinic chloride, but solutions of nicotine are. A further distinguishing test is to add 1 drop of a concentrated alcoholic solution of phenolphthalein to a solution of either base; with coniine a red colour is developed, but with nicotine there is no reaction.
Soluble in water (1 in 100) in alcohol, ether, chloroform, benzene, amyl alcohol, or acetone, but only slightly soluble in carbon bisulphide.
Action and Uses.—Coniine depresses the medulla and the motor nerve endings, so that after large doses death results from respiratory paralysis, which is mainly central—that is, the medulla is paralysed before the nerves. On the circulatory system coniine acts very like nicotine, in that it paralyses autonomic nerve-cells, after an initial stimulation, and so lowers blood pressure from paralysis of the splanchnics, and quickens the heart from paralysis of the vagi. It has been used in chorea, mania, paralysis agitans, tetanus, and strychnine poisoning for its depressant action on the motor nerves, but in this respect it is inferior to curare. In spasmodic affections such as laryngismus, whooping cough, and asthma, it is also employed. To allay cough and bronchial spasm it is best given as an inhalation. Externally, it is sedative, and especially valuable in pruritis ani and to relieve the pain of fissures, ulcerated haemorrhoids, etc. The pure alkaloid is rarely administered, coniine hydrobromide or hydrochloride being preferred. Pessaries containing 3 centimils (0.03 milliliters) (1 minim) or more of coniine in each are prepared with a glyco-gelatin basis. In cases of poisoning by coniine or its salts, the gelatin stomach should be emptied, stimulants and warmth applied, with artificial respiration if necessary. As an antidote, give strong tea or 1 to 1 ½ grammes (15 to 20 grains) of tannic acid in aqueous solution.
Dose.—1 to 10 milligrams (1/64 to ⅙ grain).