PHENAZINE, in organic chemistry, the parent substance of many dyestuffs, e.g., the eurhodines, toluylene red, indulines and safranines. (See DYES, SYNTHETIC.) It may be obtained by passing aniline vapour over lead oxide, or by the oxidation of dihydrophenazine, which is prepared by heating catechol with orthophenylenediamine. It is also formed when ortho-aminodi phenylamine is distilled over lead peroxide. It crystallizes in yellow needles which melt at I7I° C, and are only sparingly solu ble in alcohol. Its formula is C12H8N2. Sulphuric acid dissolves it, forming a deep red solution. The more complex phenazines, i.e., the naphthophenazines, naphthazines and naphthotolazines, may be prepared by condensing ortho-diamines with ortho-quinones (0. Hinsberg, 1887) ; by the oxidation of an ortho-diamine in the presence of a-naphthol (0. Witt), and by the decomposition of ortho-anilido (-toluidido-, etc.)-azo compounds with dilute acids. If alkyl or aryl-ortho-diamines be used azonium bases are obtained. The azines are mostly yellow in colour, distil unchanged and are stable to oxidants. They add on alkyl iodides readily, forming alkyl azonium salts.
The symmetrical diaminophenazine is the parent substance of the important dyestuff toluylene red or dimethyldiaminotoluphen azine. It is obtained by the oxidation of orthophenylenediamine with ferric chloride; by oxidizing a mixture of para-aminodime thylaniline and meta-tolylenediamine, toluylene blue, an inda mine, being formed as an intermediate product and passing into the red when boiled ; and also by the oxidation of dimethyl paraphenylenediamine with metatolylenediamine. 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. Phenazonium salts are known as safranines. (See DYES, SYNTHETIC.) Phenazone or dibenzopyridazine is an isomeride of phenazine, to which it bears the same relation that phenanthrene bears to anthracene (qq.v.). It is formed by reducing diortho-dinitro diphenyl with sodium amalgam and methyl alcohol. It crystallizes in yellow needles which melt at 156° C. Potassium permanganate oxidizes it to pyridazinetetracarboxylic acid.