a-Aminoquinoline can be obtained directly from quinoline by treatment with sodamide, as well as by the usual methods for preparation of amino derivatives. The aminoquinolines can be diazotized and coupled to form azo dyes in the same way as aniline, but they are not of great use.
Of the homologues of quinoline, the most im portant are quinaldine, lepidine and -y-phenylquinoline. Quinal dine is a-methylquinoline and is present in coal tar, forming about 25% of the quinoline fraction. It may be readily prepared syn thetically by condensing aniline with acetaldehyde by means of hydrochloric acid. It is a colourless liquid, b.p. 247° C. The methyl group is very reactive, condensing readily with aldehydes, and with phthalic anhydride to form the dye known as quinoline yellow. A red isocyanine dye is prepared by treating the mixed ethiodides of quinoline and quinaldine with alcoholic potash. Lepidine or y-methylquinoline also occurs in coal tar. It is pro duced when the alkaloid cinchonine is distilled with potash. Simi larly y-phenylquinoline is related to the quinia alkaloids. Many of the higher homologues of quinoline have been found among the coal tar bases.
Chromic acid oxidizes the methylquinolines to the correspond ing quinolinecarboxylic acids. Potassium permanganate produces pyridinetricarboxylic acids.
Certain quinoline derivatives find use in medicine for antiseptic, antifebrile and analgesic purposes. The base itself has been used as an insecticide. Isoquinoline,
the isomeride of quinoline was discovered in coal tar in 1885, but forms only about 1.5% of the quinoline fraction. It has the constitution shown in the formula, which is confirmed by its synthesis and oxidation products. It was sepa rated from the quinoline in coal tar by the frac tional crystallization of the mixed sulphates. Isoquinoline can be prepared synthetically by passing benzylidene-ethylamine through a hot tube and by the reduction of homophthalimide. It is a solid, m.p. 23° C, and boils at 24o° C. As a tertiary amine and a mono-acid base, it has many reactions in common with quinoline. It is the parent body of many alkaloids. Its most important use is for the preparation of quinoline red, a dye employed as a photo-sensitizer. (J. Ro.)