Phenazine is an organic compound with the formula (C6H4)2N2. It is a dibenzo annulation pyrazine, and the parent substance of many , such as the toluylene red, , and (and the closely related eurhodines).
Synthesis
Classically phenazine are prepared by the reaction of nitrobenzene and aniline in the Wohl–Aue reaction. Other methods include:
Derivatives
-
The more complex phenazines, such as the , , and , may be prepared by condensing Toluidine with quinone
-
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 . They add on readily, forming alkyl azonium salts, anhydride formation also taking place between these . It dissolves in concentrated sulfuric acid with a yellowish-green fluorescence.
-
The , 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 hydrolytic dissociation in aqueous solution. When heated with concentrated hydrochloric acid the amino group is replaced by the hydroxyl group and the 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 (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. [Benzo(c)cinnoline|Benzo[ccinnoline]] is an isomer of phenazine, to which it bears the same relation that phenanthrene bears to anthracene.
Natural products
The known biological sources of phenazine compounds are mostly bacterial in nature.
While bacterial phenazines are principally involved in secondary metabolisms, methanophenazine in methanogenic archaea (Methanogen) is involved in primary metabolisms and are important electron carriers.
Biosynthesis
Phenazine biosynthesis branches off the Shikimic acid 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 .
