It is well known that in coal-tar is found a series of ammonia-like bases, aniline or amido-benzol, toluidine or amido-toluol, and xylidine or amido-xylol, which are utilized practically in the manufacture of the so-called aniline dye-colors. It is perhaps not so well known that there are other series of bases found there too. The first of these is the pyridine series, including pyridine, CHN, picoline (methyl-pyridine), CHN(CH), lutidine (dimethyl-pyridine), CHN(CH), and collidine (trimethyl-pyridine), CHN(CH). This series is also found in relatively larger proportion in what is known as Dippel's oil, the product of the dry distillation of bones.
The second series is the quinoline series, including quinoline, CHN, lepidine (methyl-quinoline), CHN, and cryptidine (dimethyl-quinoline), CHN. The two compounds which give name to these series, pyridine, CHN, and quinoline, CHN, respectively, bear to each other a relation analogous to that existing between benzol, CH, and naphthalene, CH; and the theory generally accepted by those chemists who have been occupying themselves with these bases and their derivatives is that pyridine is simply benzol, in which an atom of nitrogen replaces the triad group, CH, and quinoline, the naphthalene molecule with a similar change. Indeed, Ladenberg has recently succeeded in obtaining benzol as an alteration product from pyridine, in certain reactions. Moreover, from methyl-pyridine, CHN(CH), would be derived an acid know as pyridine-carboxylic acid, CHN(COOH), just as benzoic acid, CHCOOH, is derived from methyl-benzol, CHCH, and from dimethyl-pyridine, CHN(CH), an acid known as pyridine-dicarboxylic acid, CHN(COOH), just as phthalic acid, CH(COOH), is derived from dimethyl-benzol, CH(CH). The same thing applies to quinoline as compared to naphthalene.
We may now look at the question of the decomposing effect of reagents upon the alkaloids. The means which have proved most efficacious in decomposing these bases are the action of oxidizing and reducing agents, of bromine, of organic iodides, of concentrated acids and alkalies, and of heat.
Taking up the volatile alkaloids, we find with regard to conine, first, that the action of methyl iodide shows it to be a secondary amine, that is, it restrains only one replaceable hydrogen atom of the original ammonia molecule. Its formula is therefore CHNH. From conine can be prepared methyl-conine, which also occurs in nature, and dimethyl-conine. From this latter has been gotten a hydrocarbon, CH, conylene, homologous with acetylene, CH. Conine, on oxidation, yields chiefly butyric acid, but among the products of oxidation has been found the pyridine carboxylic acid before referred to. The formula of conine, CHN, shows it to be homologous with piperidine, CHN, a derivative of piperine, the alkaloid of pepper, to be spoken of later; and, just as piperidine is derived from pyridine by the action of reducing agents, so conine is probably derived from a propyl-pyridine. The artificial alkaloid paraconine, isomeric with the natural conine, will be referred to later.
Nicotine, CHN, the next simplest in formula of the alkaloids, is a tertiary base, that is, contains no replaceable hydrogen atoms in its molecule. It shows very close relations to pyridine. When nicotine vapor is passed through a red-hot tube, it yields essentially collidine, and, with this, some pyridine, picoline, lutidine, and gases such as hydrogen, marsh-gas, and ethylene. Heated with bromine water to 120°C. it decomposes into bromoform, carbon dioxide, nitrogen, and pyridine. When its alcoholic solution is treated with ferricyanide of potassium it is oxidized to dipyridine, CHN. Potassium permanganate, chromic or nitric acid oxidises it to nicotinic acid, CHNO, which is simply pyridine-carboxylic acid, CHN(COOH), and which, distilled over quick-lime, yields pyridine, CHN.
Turning now to the non-volatile and oxygenized bases, we take up first the opium alkaloids. Morphine, CHNO, is a tertiary amine, and appears to contain a hydroxyl group like phenols, to which class of bodies it has some analogies, as is shown in its reaction with ferric chloride. Its meythl ester, which can be formed from it, is codeine, one of the accompanying alkaloids of opium. Besides the methyl derivative, however, others are possible, and several have been recently prepared, giving rise to a class of artificial alkaloids known as codeines. Morphine, rapidly distilled over zinc dust, yields phenanthren, trimethyl-amine, pyrrol, pyridine, quinoline, and other bases. The action of strong hydrocholoric acid upon morphine changes it into apomorphine, CHNO, by the withdrawal of a molecule of water. Ferricyanide of potassium and caustic soda solution change morphine into oxidimorphine, CHNO. When heated with strong potassium hydrate, it yields methylamine.
Narcotine, another of the opium alkaloids, when heated with manganese dioxide and sulphuric acid, is oxidized and splits apart into opianic acid, CHO, and cotarnine, CHNO. This latter, by careful oxidation, yields apophyllenic acid, CHNO, and this, on heating with hydrochloric acid to 240° C., yields pyridine-dicarboxylic acid, CHN(COOH). The base cotarnine also results from the prolonged heating of narcotine with water alone. In this case, instead of opianic acid, its reduction product meconine, CHO, is produced.
Meconic acid, CHO, which is found in opium in combination with the different bases, has also been investigated. By acting upon meconic acid with ammonia, comenamic acid is formed, and this latter, when heated with zinc dust, yields pyridine.
If we go now to the cinchona alkaloids, we meet with exceedingly interesting results. Quinine, CHNO, when carefully oxidized with chromic acid or potassium permanganate, yields a series of products. First is formed quitenine, CHNO, a weak base, then quininic acid, CHNO, then the so-called oxycinchomeronic acid, CHN0, and finally cinchomeronic acid, CHNO. Now the two acids last mentioned are simple substitution products of pyridine, oxycinchomeronic acid being a pyridine-dicarboxylic acid, CHN(COOH), and cinchomeronic acid, a pyridine-dicarboxylic acid, CHN(COOH). When distilled with potassium hydrate, quinine yields quinoline and its homologues. The alkaloid has been shown to be a tertiary base.