1911 Encyclopædia Britannica/Safranine

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SAFRANINE, in chemistry, the azonium compounds of symmetrical diamino-phenazine and containing the ring system annexed:-

They are obtained by the joint oxidation of one molecule of a paradiamine with two molecules of a primary amine; by the condensation of para-aminoazo compounds with primary amines (O. Witt, Ber., 1877, 10, p. 874), and by the action of para-nitrosodialkylanilines with secondary bases such as diphenylmetaphenylenediamine. They are crystalline solids showing a characteristic green metallic lustre; they are readily soluble in water and dye red or violet. They are strong bases and form stable monacid salts. Their alcoholic solution shows a yellow-red fluorescence.

Phenosafranine is not very stable in the free state; its chloride forms green plates. It can be readily diazotized, and the diazonium salt when boiled with alcohol yields aposafranine or benzene induline, C18H12N3. F. Kehrmann showed that aposafranine could be diazotized in the presence of cold concentrated sulphuric acid, and the diazonium salt on boiling with alcohol yielded phenylphenazonium salts. Aposafranone, C18H12N2O, is formed by heating aposafranine with concentrated hydrochloric acid. These three compounds are perhaps to be represented as ortho- or as paraquinones (see papers by F. Kehrmann, O. Fischer and E. Hepp; R. Nietzki and others, Ber., 1895 et seq.). The “safranine” of commerce is a tolusafranine. The first aniline dye-stuff to be prepared on a manufacturing scale was mauveine, C27H25N4Cl, which was obtained by Sir W. H. Perkin by heating crude aniline with potassium bichromate and sulphuric acid. It is a N-phenylsafranine (see Indulines).