Phenazine (C12H8N2 or C6H4N2C6H4), also called azophenylene, dibenzo-p-diazine, dibenzopyrazine, and acridizine, is a dibenzo annulated pyrazine and the parent substance of many dyestuffs, such as the eurhodines, toluylene red, indulines and safranines.
A classic method for the synthesis of phenazine is the reaction of nitrobenzene and aniline in the Wohl-Aue reaction
(1901). Other methods are known, e.g.:
Phenazine crystallizes in yellow needles which melt at 174-177 °C, and are only sparingly soluble in alcohol. Sulfuric acid dissolves it, forming a deep-red solution.
- 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-(-toluidido- et cetera)- 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 hydrolytic dissociation in aqueous solution. When heated with concentrated hydrochloric acid the amino group is replaced by the hydroxyl group and the phenolic eurhodols are produced.
diaminophenazine is the parent substance of the important dyestuff toluylene red
or dimethyldiaminotoluphenazine. It is obtained by the oxidation of orthophenylene diamine
with ferric chloride
; when a mixture of para-aminodimethylaniline and meta-toluylenediamine is oxidized in the cold, toluylene blue, an indamine, being 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
is an isomer
of phenazine, to which it bears the same relation that phenanthrene
bears to anthracene
Many phenazine compounds are found in nature and are produced by bacteria such as Pseudomonas
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