1911 Encyclopædia Britannica/Conine
CONINE, or Coniine (α-propyl piperidine), C8H17N, an alkaloid occurring, associated with γ-coniceine, conhydrine, pseudoconhydrine and methyl conine, in hemlock (Conium maculatum). It is a colourless oily liquid of specific gravity 0.845 (20° C.), boiling at 166° C., almost insoluble in water, soluble in ether and in alcohol. It has a sharp burning taste and a penetrating smell, and acts as a violent poison. It is dextro-rotatory. The alkaloid is a strong base and is very readily oxidized; chromic acid converts it into normal butyric acid and ammonia; hydrogen peroxide gives aminopropylvalerylaldehyde, NH2⋅CH(C3H7)⋅(CH2)3⋅CHO, whilst the benzoyl derivative is oxidized by potassium permanganate to benzoyl-α-aminovaleric acid, C6H5CO⋅NH⋅CH(C3H7)⋅(CH2)3⋅COOH. It combines directly with methyl iodide to form dimethyl coninium iodide, C10H22NI, which by the destructive methylation process of A. W. Hofmann (Berichte, 1881, 14, pp. 494, 659) is converted into the hydrocarbon conylene C8H14, a compound that can also be obtained by heating nitrosoconine with phosphoric an hydride to 80-90° C. On heating conine with concentrated hydriodic acid and phosphorus it is decomposed into ammonia and normal octane C8H18. Conine is a secondary base, forming a nitroso derivative with nitrous acid, a urethane with chlorcarbonic ester and a tertiary base (methyl conine) with methyl iodide; reactions which point to the presence of the =NH group in the molecule.
It was the first alkaloid to be synthesized, a result due to A. Ladenburg (see various papers in the Berichte for the years 1881, 1884, 1885, 1886, 1889, 1893, 1894, 1895, and Liebig’s Annalen for 1888, 1894). A. W. Hofmann had shown that conine on distillation with zinc dust gave α-propyl pyridine (conyrine). This substance when heated with hydriodic acid to 300° C. is converted into α-propyl piperidine, which can also be obtained by the reduction of α-allyl pyridine (formed from a-methyl pyridine and paraldehyde). The α-propyl piperidine so obtained is the inactive (racemic) form of conine, and it can be resolved into the dextro- and laevo-varieties by means of dextro-tartaric acid, the d-conine d-tartrate with caustic soda giving d-conine closely resembling the naturally occurring alkaloid. A. Ladenburg (Ber. 1906, 39, p. 2486) showed that the difference in the rotations of the natural and synthetic d-conine is not due to another substance, iso-conine, as was originally supposed, but that the artificial product is a stereo-isomer, which yields natural conine on heating for some time to 290°-300°, and then distilling.
γ-Coniceine, C8H15N, is a tetrahydro conyrine, i.e. a tetra-hydro propyl pyridine. It may be obtained by brominating conine, and then removing the elements of hydrobromic acid with alkalis. Other coniceines have been prepared. Conhydrine, C8H17NO, and pseudoconhydrine are probably stereo-isomers, the latter being converted into the former when boiled with ligroin. Since conhydrine is dehydrated by phosphorus pentoxide into a mixture of α and β coniceines, it may be considered an oxyconine. Methyl conine, C9H19N or C8H14⋅N(CH3), is synthesized from conine and an aqueous solution of potassium methyl sulphate at 100°.