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FUCHSINE, or MAGENTA

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Originally appearing in Volume V11, Page 273 of the 1911 Encyclopedia Britannica.
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FUCHSINE, or See also:MAGENTA , a red dyestuff consisting of a mixture of the hydrochlorides or acetates of pararosaniline and rosaniline. It was obtained in 1856 by J. Natanson (See also:Ann., 1856, 98, p. 297) by the See also:action of See also:ethylene chloride on See also:aniline, and by A. W. See also:Hofmann in 1858 from aniline and See also:carbon tetrachloride. It is prepared by oxidizing " aniline for red " (a mixture of aniline and ortho- and See also:para-toluidine) with See also:arsenic See also:acid (H. Medlock, Dingler's Poly. Jour., 186o, 158, p. 146); by See also:heating aniline for red with See also:nitrobenzene, concentrated hydrochloric acid and See also:iron (Coupier, Ber., 1873, 6, p. 423) ; or by condensing formalde-. See also:hyde with aniline and ortho-toluidine and oxidizing the mixture. It forms small crystals, showing a brilliant See also:green reflex, and is soluble in See also:water and See also:alcohol with formation of a deep red See also:solution.

It dyes See also:

silk, See also:wool and See also:leather See also:direct, and See also:cotton after mordanting with See also:tannin and See also:tartar emetic (see See also:DYEING). An aqueous solu- .273 tion of fuchsine is decolorized on the addition of sulphurous acid, the easily soluble fuchsine sulphurous acid being formed. This solution is frequently used as a test reagent for the detection of See also:aldehydes, giving, in most cases, a red coloration on the The constitution of the fuchsine bases (pararosaniline and rosaniline) was determined by E. and O. See also:Fischer in 1878 (Ann., 1878, 194, p. 242); A. W. Hofmann having previously shown that oxidation of pure aniline alone or of pure toluidine yielded no fuchsine, whilst oxidation of a mixture of aniline and para-toluidine gave rise to the See also:fine red dyestuff para-fuchsine (pararosaniline hydro-chloride) CH,.C6H4NH2+2C6H5NH2+30 se- HO.C(C21-1sNH2) +2H20. See also:Colour See also:base (pararosaniline). H0.C(CsH4NH2)3•HC1=H20+(H2N•C6H4)2C : See also:C6H4 : NH2C1. Pararosaniline hydrochloride. A. Rosenstiehl (Jahres., 1869, p.

693) found also that different rosanilines were obtained according to whether ortho- or para-toluidine was oxidized with aniline, and he gave the name rosaniline to the one obtained from aniline and ortho-toluidine, reserving the See also:

term pararosaniline for the other. E. and O. Fischer showed that these compounds were derivatives of See also:triphenylmethane and tolyldiphenylmethane respectively. Pararosaniline was reduced to the corresponding leuco See also:compound (paraleucaniline), from which by diazotization and boiling with alcohol, the See also:parent See also:hydrocarbon was obtained (H2N•C5H4)2C:C6H4:NH2Cl-->HC(C,H4NHs. H Cl)3 -HC(C6H4N2Cls) Pararosaniline hydrochloride. Paraleucaniline. ->HC(CsH6)3. Triphenylmethane. The See also:reverse See also:series of operations was also carried out by the Fischers, triphenylmethane being nitrated, and the nitro compound then reduced to triaminotriphenylmethane or paraleucaniline, which on careful oxidation is converted into the dyestuff. A similar series of reactions was carried out with rosaniline, which was shown to be the corresponding derivative of tolyldiphenylmethane. The See also:free pararosaniline, C,9H19N30, and rosaniline, C25H21N30, may be obtained by precipitating solutions of their salts with a See also:caustic See also:alkali, colourless precipitates being obtained, which crystallize from hot water in the See also:form of needles or plates. The position of the amino See also:groups in pararosaniline was determined by the See also:work of H.

See also:

Caro and C. Graebe (Ber., 1878, II, p. 1348) and of E. and O. Fischer (Ber., 188o, 13, p. 2204) as follows: Nitrous acid converts pararosaniline into aurin, which when superheated with water yields para-dioxybenzophenone. As the hydroxyl groups in aurin correspond to the amino groups in pararosaniline, two of these in the latter compound must be in the para position. The third is also in the para position; for if See also:benzaldehyde be condensed with aniline, condensation occurs in the para position, for the compound formed may be converted into para-dioxybenzophenone, See also:C6H5CHO--> C6H5CH (C6H4NH2)2-->C6H5CH (C6H4OH))2 _K(C6H40H)2 ; but if para-nitrobenzaldehyde be used in the above reaction and the resulting nitro compound NO2•C6Hs.CH(C6H4NH2)2 be reduced, then pararosaniline is the final product, and consequently the third amino See also:group occupies the para position. Many derivatives of pararosaniline and rosaniline are known, in which the See also:hydrogen atoms of the amino groups are replaced by alkyl groups; this has the effect of producing a See also:blue or See also:violet shade, which becomes deeper as the number of groups increases (see DYEING).

End of Article: FUCHSINE, or MAGENTA

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