Acridine is an organic compound and a nitrogen heterocyclic ring, and its molecular formula is C13H9N. Acridine is a substituted derivative of the parent ring. This is a planar molecule that is structurally related to anthracene and one of the central CH groups is replaced by nitrogen. Like related molecules, pyridine and quinoline, apyridine is weakly basic, which is an almost colorless solid. Commercial pyridine has no commercial application, but atidine dyes were once popular. It crystallizes in the needle.
Figure 1. Acridine chemical structure.
Carl Gräbe and Heinrich Caro first isolated acridine from coal tar in 1870. From was separated from coal tar by extraction with dilute sulfuric acid. To this solution was added potassium dichromate to precipitate idine dichromate. Dichromate is decomposed with ammonia. Acridine and its derivatives can be prepared by many synthetic methods. In the Bernson a-pyridine synthesis, diphenylamine is condensed with a carboxylic acid in the presence of zinc chloride. When formic acid is a carboxylic acid, the reaction produces the parent aidine. With higher and larger carboxylic acids, derivatives substituted on meso carbon atoms are formed. Other older methods for the organic synthesis of acridine include the condensation of diphenylamine with chloroform in the presence of aluminum chloride, passing the vapor of o-aminodiphenylmethane through heated calcium carbonate, and heating salicylaldehyde with aniline and zinc chloride or distilled or pyridone (9-position carbonyl)) covered with zinc powder. Another classical method for the synthesis of amidone is the Lehmstedt-Tanasescu reaction.
Figure 2. The Bernthsen acridine synthesis.
The acridine shows the expected reaction of an unsaturated N-heterocycle. It undergoes N-alkylation reaction with alkyl iodide to form alkyl cripyridinium iodide. The alkyl iodide iodide is easily converted into N-alkyl apyridone by the action of basic potassium ferricyanide.
Acridine can be reduced to 9,10-dihydroacidine, sometimes also called colorless apyridine. Reaction with potassium cyanide gives 9-cyano-9,10-dehydrogenated derivatives. Oxidation with potassium permanganate will produce a picolinic acid (C9H5N (CO2H)2), also known as quinoline 1,2-dicarboxylic acid. Peridine is easily oxidized by peroxymonosulfuric acid to the pyridine amine oxide. The 9-position carbon of activated pyridine is activated for the addition reaction.
At one time acridine dyes were commercially significant, but they are now uncommon because they are not lightfast. Acridine dyes are prepared by condensation of 1,3-diaminobenzene derivatives. Illustrative is the reaction of 2,4-diaminotoluene with acetaldehyde:
Figure 3. Synthesis of C.I. Basic Yellow 9, an acridine dye.
9-phenylacridine is the parent base of Chssaniline or 3,6-diamino-9-phenylacridine. It is the main component of the dye phosphine (not to be confused with phosphine gas). This dye is a by-product of making rosaniline. O-xylylenediamine forms a red salt, which dyes silk and wool to pale yellow. The salt solution is characterized by its fine yellow-green fluorescence. O. Fischer and G. Koerner synthesized phthalamide by condensing o-nitrobenzaldehyde and aniline, and reduced the resulting o-nitro-p-diaminotriphenylmethane to the corresponding o-amino compound. Oxidation to phthalamide. An isomer of acetophenone, benzoflavone, is also a dye made by K. Oehler from m-phenylenediamine and benzaldehyde. These materials condense to form tetraaminotriphenylmethane, which will lose ammonia when heated with acid, and generate 3,6-diamino-9,10-dihydrophenylacridine, which can be obtained by oxidation. It is a yellow powder that dissolves in hot water.