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, such as proflavine, also have antiseptic properties. 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. Acridarsine is formally derived from acridine by replacing the nitrogen atom with one of arsenic, and acridophosphine by replacing it with one of phosphorus.
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 classic method for the synthesis of acridones is the Lehmstedt-Tanasescu reaction.
Numerous derivatives of acridine are known and may be prepared by methods analogous to those used for the formation of the parent base. 9-Phenylacridine 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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