Phenazine is an organic compound with the formula 2N2. It is a dibenzo annulatedpyrazine, and the parent substance of many dyestuffs, such as the toluylene red, indulines, and safranines. Phenazine crystallizes in yellow needles, which are only sparingly soluble in alcohol. Sulfuric acid dissolves it, forming a deep-red solution.
oxidation of ortho-aminodiphenylamine with lead peroxide.
Derivatives
The more complex phenazines, such as the naphthophenazines, naphthazines, and naphthotolazines, may be prepared by condensing ortho-diamines with ortho-quinones or by the oxidation of an ortho-diamine in the presence of α-naphthol, and by the decomposition of ortho-anilido-- azo compounds with dilute acids.
If alkyl or aryl-ortho-diamines be used, azonium bases are obtained. The azines are mostly yellow in color, distill unchanged and are stable to oxidants. They add on alkyl iodides readily, forming alkyl azonium salts, anhydride formation also taking place between these hydroxylgroups. It dissolves in concentrated sulfuric acid with a yellowish-green fluorescence.
The rhodamines, which are closely related to the phthaleins, are formed by the condensation of the alkyl metaaminophenols with phthalic anhydride in the presence of sulfuric acid. Their salts are fine red dyes. By the entrance of amino or hydroxyl groups into the molecule dyestuffs are formed. The mono-amino derivatives or eurhodines are obtained when the arylmonamines are condensed with orthoamino azo compounds; by condensing quinone dichlorimide or para-nitrosodimethyl aniline with monamines containing a free para position, or by oxidizing ortho-hydroxydiaminodipbenylamines. They are yellowish-red solids, which behave as weak bases, their salts undergoing hydrolyticdissociation in aqueous solution. When heated with concentrated hydrochloric acid the amino group is replaced by the hydroxyl group and the phenolic eurhodols are produced.
Aminophenazine
Many aminophenazines are prominent dyes. Two of the first synthetic dyes are aminophenazines, these include induline and nigrosin. The symmetrical diaminophenazine is the parent substance of the important dyestuff neutral red. It is obtained by the oxidation of ortho-phenylenediamine with ferric chloride. In a related process, oxidation of a coldmixture of para-aminodimethylaniline and meta-toluylenediamine gives toluylene blue. This indamine is formed as an intermediate product and passing into the red when boiled; and also by the oxidation of dimethylparaphenylene diatnine with metatoluylene diamine. It crystallizes in orange-red needles and its alcoholic solution fluoresces strongly. It dyes silk and mordanted cotton a fine scarlet. It is known commercially as neutral red. For the phenazonium salts, see safranine. Benzocinnoline|Benzocinnoline is an isomer of phenazine, to which it bears the same relation that phenanthrene bears to anthracene.
The only known biological sources of phenazine compounds are bacterial in nature. Some of the genera known to produce phenazines include Pseudomonas spp., Streptomyces spp., and Pantoea agglomerans. These phenazine natural products have been implicated in the virulence and competitive fitness of producing organisms. For example, the phenazine pyocyanin produced by Pseudomonas aeruginosa contributes to its ability to colonise the lungs of cystic fibrosis patients. Similarly, phenazine-1-carboxylic acid, produced by a number of Pseudomonas, increases survival in soil environments and has been shown to be essential for the biological controlactivity of certain strains.
Biosynthesis
Phenazine biosynthesis branches off the shikimic acid pathway at a point subsequent to chorismic acid. Two molecules of this chorismate-derived intermediate are then brought together in a diagonally-symmetrical fashion to form the basic phenazine scaffold. Sequential modifications then lead to a variety of phenazine with differing biological activities. An example of phenazinic alkaloids are pyocyanin, saphenic acid and esmeraldins.
