1911 Encyclopædia Britannica/Safranine

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).