ACRIDINE is a solid, crystallizing in needles of melting point 1o° C, found in coal-tar anthracene. It is characterized by its irritating action on the skin, and by the blue fluorescence shown by solutions of its salts. It is extracted from the crude anthracene by dilute sulphuric acid ; the sulphuric acid solution is treated with potassium dichromate, and the precipitate of sparingly soluble acridine dichromate is decomposed with ammonia (C. Graebe and H. Caro, Ann. 1871).
Acridine and its homologues are stable compounds of feebly basic character, belonging to the general class of heterocyclic ring compounds (see CHEMISTRY : Organic). They combine readily with the alkyl iodides to form alkylacridinium iodides, which are readily transformed by the action of alkaline potassium ferricya nide to N-alkylacridones.
Acridine itself has the structural formula It owes its basic properties to the presence of the tertiary ni trogen atom; it may be regarded as consisting of two benzene nuclei fused to a partially reduced pyridine nucleus, and shows characteristics both of the former (homocyclic) and the latter (heterocyclic) structure.
Phenyl-acridine is the parent base of chrysaniline, the chief constituent of the dyestuff phosphine (a by-product in the manu facture of rosaniline). The dyestuff phosphine must be distin guished from the phosphorus hydride of the same name, and from the organic derivatives of this substance, to which the general term phosphine is also given. Chrysanaline (diamino-phenylacridine) forms red salts, dyeing silk and wool a fine yellow; the solutions of the salts are characterized by their fine yellowish-green fluorescence.
Several acridine derivatives and notably acriflavine (syn. trypa flavine, euflavine) found extensive use during the World War as antiseptics for infected wounds (C. H. Browning and others). The preparation of acriflavine (I.) and of proflavine, another acridine antiseptic of similar type, was described by L. Benda Rivanol (II.) also of the acridine series is recommended by J. Morgenroth (1921) as a powerful tissue antiseptic against spread ing infection due to streptococcus.