Phenazine

Phenazine is an organic compound with the formula (C6H4)2N2. It is a dibenzo annulated pyrazine, and the parent substance of many dyestuffs, such as the toluylene red, indulines, and safranines (and the closely related eurhodines). Phenazine crystallizes in yellow needles, which are only sparingly soluble in alcohol. Sulfuric acid dissolves it, forming a deep-red solution. Phenazine is an organic compound with the formula (C6H4)2N2. It is a dibenzo annulated pyrazine, and the parent substance of many dyestuffs, such as the toluylene red, indulines, and safranines (and the closely related eurhodines). Phenazine crystallizes in yellow needles, which are only sparingly soluble in alcohol. Sulfuric acid dissolves it, forming a deep-red solution. Classically phenazine are prepared by the reaction of nitrobenzene and aniline in the Wohl-Aue reaction). Other methods include: 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 (dimethyldiaminotoluphenazine). It is obtained by the oxidation of ortho-phenylenediamine with ferric chloride. In a related process, oxidation of a cold mixture 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 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 control activity of certain strains. 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.  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). 'Phenazine'. Encyclopædia Britannica. 21 (11th ed.). Cambridge University Press. pp. 364–365.