Acridine

Acridine, C13H9N, is an organic compound and a nitrogen heterocycle. Acridine is also used to describe compounds containing the C13N tricycle.

Acridine is structurally related to anthracene with one of the central CH groups is replaced by nitrogen. Acridine, a colorless solid, was first isolated from coal tar. It is a raw material used for the production of dyes and some valuable drugs. Many acridines also have antiseptic properties such as Proflavine. Acridine and related derivatives bind to DNA and RNA due to their abilities to intercalate. Acridine Orange (3,6-dimethylaminoacridine) is a nucleic acid-selective metachromatic stain useful for cell cycle determination.

History
Acridine was first isolated in 1871 by Carl Gräbe and Heinrich Caro.

Physical properties
Acridine and its homologues are stable compounds of feebly basic character. Acridine has a pKa of 5.6, which is similar to that of pyridine. It also shares properties with quinoline which is the single fused homologue. 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.

Chemical properties
Acridine combines readily with alkyl iodides to form alkyl acridinium iodides, which are readily transformed by the action of alkaline potassium ferricyanide to N-alkyl acridones. On oxidation with potassium permanganate it yields acridinic acid C9H5N(COOH)2 or quinoline-1,2-dicarboxylic acid. Acridine is easily oxidized by peroxymonosulfuric acid to the acridine amine oxide. The carbon 9-position of acridine is activated for addition reactions. The compound is reduced to the 9,10-dehydroacridine and reaction with potassium cyanide gives the 9-cyano-9,10-dehydro derivative.

Numerous derivatives of acridine are known and may be prepared by methods analogous to those used for the formation of the parent base. Phenylacridine (9-phenyl-acridine) is the parent base of chrysaniline or 3,6-diamino-9-phenylacridine, which is the chief constituent of the dyestuff phosphine (not to be confused with phosphine gas), a by-product in the manufacture of rosaniline.

Chrysaniline 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. Chrysaniline was synthesized by O. Fischer and G. Koerner 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 from meta-phenylenediamine and benzaldehyde. These substances condense to form tetra-aminotriphenylmethane, which, on heating with acids, loses ammonia and yields 3,6-diamino-9,10-dihydrophenylacridine, from which benzoflavin is obtained by oxidation. It is a yellow powder, soluble in hot water.

Cancer link
Acridine is a known human carcinogen.