Nicotine

Nicotine, C10H14N2, an alkaloid, found with small quantities of nicotimine, C 19 H 14 N 2, nicoteine, C10H12N2, and nicotelline, C 10 H 8 N 2, in tobacco. The name is taken from Nicotiana, the tobacco plant, so called after Jean Nicot (1530-1600), French ambassador at Lisbon, who introduced tobacco into France in 1560. These four alkaloids exist in combination in tobacco chiefly as malates and citrates. The alkaloid is obtained from an aqueous extract of tobacco by distillation with slaked lime, the distillate being acidified with oxalic acid, concentrated to a syrup and decomposed by potash. The free base is extracted by ether and fractionated in a current of hydrogen. It is a colourless oil, which boils at 247° C. (745 mm.), and when pure is almost odourless. It has a sharp burning taste, and is very poisonous. It is very hygroscopic, dissolves readily in water, and rapidly undergoes oxidation on exposure to air. The free alkaloid is strongly laevo-rotatory. F. Ratz (Monats., 1905, 26, p. 1241) obtained the value [a] D = - 16 9.54° at 20°; its salts are dextro-rotatory. It behaves as a di-acid as well as a di-tertiary base.

On oxidation with chromic or nitric acids, or potassium permanganate, it yields nicotinic acid or (3-pyridine carboxylic acid, C 5 H 4 NCO 2 H; alkaline potassium ferricyanide gives nicotyrine, C10H10N2, and hydrogen peroxide oxynicotine, C10H14N20. Oxidation of its isomethylhydroxide with potassium permanganate yields trigonelline, C 7 H 7 NO 2 (A. Pictet and P. Genequand, Ber., 1897, 30, p. 2117). It gives rise to various decomposition products such as pyridine, picoline, &c., when its vapour is passed through a red-hot tube. The hydrochloride on heating with hydrochloric acid gives methyl chloride (B. Blau, Ber., 1893, 26, p. 631). Hydriodic acid and phosphorus at high temperature give a dihydro-compound, whilst sodium and alcohol give hexaand octo-hydro derivatives. Nicotine may be recognized by the addition of a drop of 30% formaldehyde, the mixture being allowed to stand for one hour and the solid residue then moistened by a drop of concentrated sulphruic acid, when an intense rose-red colour is produced (I. Schindelmeiser, Pharm. Zentralhalle, 18 99, 40, p. 704).

The constitution of nicotine was established by A. Pinner (see papers in the Berichte, 1891 to 1895). With bromine in acetic acid solution at ordinary temperature, nicotine yields a perbromide, C10H10Br2N20 HBr 3, which with sulphur dioxide, followed by potash, gives dibromcotinine, C10H10Br2N20, from which cotinine, C10H12N20, is obtained by distillation over zinc dust. By heating nicotine with bromine in hydrobromic acid solution for some hours at 100° C., dibromticonine hydrobromide, C10H8N2Br202HBr, results. Dibromcotinine on hydrolysis yields oxalic acid, methylamine and 0-methyl pyridyl ketone: C10H10Br2N20+3H20+0= H2C204-ECH 3 NH 2 +C 5 H 4 N000H 3 +2HBr; whilst dibromticonine yields methylamine, malonic acid and nicotinic acid: C10H8Br2N202+ 4H20=CH 3 NH 2 +CH 2 (CO 2 H) 2 +C 5 H 4 NCO 2 H+2HBr, or if heated with zinc and caustic potash, methylamine and pyridyl-ay-dioxybutyric acid. Thus the groupings J_CC - - CC - >NCH 3 and - CCC N exist in the molecule, and the alkaloid is to be represented as a-pyridyl-N-methyl-pyrollidine.

This result has been confirmed by its synthesis by A. Pictet and P. Crepieux (Comptes rendus, 1903, 137, p. 860) and Pictet and Rotschy (Ber., 1904, 37, p. 1225): ,-aminopyridine is converted into its mucate, which by dry distillation gives N-13-pyridylpyrrol. By passing the vapour of this compound through a red-hot tube, it yields the isomeric a0- pyridylpyrrol, the potassium salt of which with methyl iodide gives a substance methylated both in the pyridine and pyrrol nuclei. By distillation over lime, the methyl group is removed from the pyridine ring, and the resulting a- pyridyl-Nmethylpyrrol gives i-nicotine on reduction. This base is resolved into its active components by d-tartaric acid, l-nicotine-d-tartrate crystallizing out first. The natural (laevo) base is twice as toxic as the dextro. The following formulae are important: N - CH C =CH/ - CHCH2 CH CH C/ NH CH / N CH2 N / N / N % CH CH H3C CH2 N-fl-Pyridylpyrrol, a0-pyridylpyrrol, nicotine.

Acetyl and benzoyl derivatives of nicotine on hydrolysis do not yield nicotine, but an isomeric, inactive oily liquid (metanicotine). It is a secondary base, and boils at 275 °-278° C.

Nicotimine is a colourless liquid which boils at 250 0 -255° C. Its aqueous solution is alkaline. Nicoteine is a liquid which boils at 267° C. It is separated from the other alkaloids of the group by distilling off the nicotine and nicotimine in steam and then fractionating the residue. It is soluble in water and is very poisonous. Nicotelline crystallizes in needles which melt at 147° C. and is readily soluble in hot water.