# 1911 Encyclopædia Britannica/Acridine

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​ACRIDINE, C$_{13}$H$_9$N, in chemistry, a heterocyclic ring compound found in crude coal-tar anthracene. It may be separated by shaking out with dilute sulphuric acid, and then precipitating the sulphuric acid solution with potassium bichromate, the resulting acridine bichromate being decomposed by ammonia. It was first isolated in 1890 by C. Graebe and H. Caro (Ann., 1871, 158, p. 265). Many synthetic processes are known for the production of acridine and its derivatives. A. Bernthsen (Ann., 1884, 224, p. 1) condensed diphenylamine with fatty acids, in the presence of zinc chloride. Formic acid yields acridine, and the higher homologues give derivatives substituted at the meso carbon atom,
Acridine may also be obtained by passing the vapour of phenylortho-toluidine through a red-hot tube (C. Graebe, Ber., 1884, 17, p. 1370); by condensing diphenylamine with chloroform, in presence of aluminium chloride (O. Fischer, Ber., 1884, 17, p. 102); by passing the vapours of orthoaminodiphenylmethane over heated litharge (O. Fischer); by heating salicylic aldehyde with aniline and zinc chloride to 260° C. (R. Mohlau, Ber., 1886, 19, p. 2452); and by distilling acridone over zinc dust (C. Graebe, Ber., 1892, 25, p. 1735).
Acridine and its homologues are very stable compounds of feebly basic character. They combine readily with the alkyl iodides to form alkyl acridinium iodides, which are readily transformed by the action of alkaline potassium ferricyanide to N-alkyl acridones. Acridine crystallizes in needles which melt at 110° C. It is characterized by its irritating action on the skin, and by the blue fluorescence shown by solutions of its salts. On oxidation with potassium permanganate it yields acridinic acid (quinolone -α-β-dicarboxylic acid) C$_9$H$_5$N(COOH)$_2$. Numerous derivatives of acridine are known and may be prepared by methods analogous to those used for the formation of the parent base. For the preparation of the naphthacridines, see F. Ullmann, German patents 117472, 118439, 127586, 128754, and also Ber., 1902, 35, pp. 316, 2670. Phenyl-acridine is the parent base of chrysaniline, which is the chief constituent of the dyestuff phosphine (a bye-product in the manufacture of rosaniline). Chrysaniline (diamino-phenylacridine) forms red-coloured salts, which dye silk and wool a fine yellow; and the solutions of the salts are characterized by their fine yellowish-green fluorescence. It was synthesized by O. Fischer and G. Koerner (Ber., 1884, 17, p. 203) by condensing ortho-nitrobenzaldehyde with aniline, the resulting ortho-nitro-para-diamino-triphenylmethane being reduced to the corresponding orthoamino compound, which on oxidation yields chrysaniline. Benzoflavin, an isomer of chrysaniline, is also a dye-stuff, and has been prepared by K. Oehler (English Patent 9614) from meta-phenylenediamine and benzaldehyde. These substances condense to form tetra-aminotriphenylmethane, which, on heating with acids, loses ammonia and yields diaminodihydrophenylacridine, from which benzoflavin is obtained by oxidation. It is a yellow powder, soluble in hot water. The formulae of these substances are:—