Acridine: Encyclopedia - Acridine

Acridine

Acridine, C₁₃H₉N, is an organic compound and a nitrogen heterocycle. The compound is similar to anthracene with the central benzene ring replaced by a pyridine ring. Acridine is colorless and was first isolated from crude coal tar. It is a raw material for the production of dyes. Many acridines also have antiseptic properties such as Proflavine. Acridine and their derivatives are DNA and RNA binding compounds due to their intercalation abilities.

Acridine Orange (3,6-dimethylaminoacridine) is a nucleic acid selective metachromatic stain useful for cell cycle determination.

Acridine - Sources

Acridine occurs naturally in coal tar. It is separated from coal tar by shaking out with dilute sulfuric acid, and then precipitating the sulfuric acid solution with potassium dichromate, the resulting acridine bichromate is decomposed in the final step by ammonia.

Many synthetic processes are known for the production of acridine and its derivatives. A. Bernthsen condensed diphenylamine with carboxylic acids, in the presence of zinc chloride in the Bernthsen acridine synthesis. With Formic acid as the carboxylic acid the reaction yields acridine itself, and with the higher homologues the derivatives substituted at the meso carbon atom are generated.

Other older methods for the organic synthesis of acridines include condensing diphenylamine with chloroform in the presence of aluminium chloride, by passing the vapours of orthoaminodiphenylmethane over heated litharge, by heating salicylic aldehyde with aniline and zinc chloride to 260°C or by distilling acridone (9-position a carbonyl group) over zinc dust.

A general method for acridine synthesis is the cyclisation of N-phenylanthranilic acid or 2-(phenylamino)benzoic acid with Phosphoric acid.

Acridine - Physical properties

Acridine and its homologues are very 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.

Acridine - 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 caro's 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.

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