Rosaniline Magenta

Nitrobenzene appears to take no part in the formation of ros-aniline, and simply acts as oxidant being converted to dyestuffs of the indnline class. When nitrobenzene is replaced by chlor-nitrobenzene, rosaniline is produced, and not, as might be expected, a chloro-derivative. Dyestuffs of the rosaniline series are formed by oxidation of numerous bases in presence of aniline and parato-luidine. Rosenstiehl and Gerber divide the homologues of aniline into three classes, according to their behaviour on oxidation with arsenic acid. 

The first class includes bases which do not yield a magenta on oxidation alone, but do if oxidised in presence of aniline. These bodies are paratoluidine, asymmetric a-metaxylidine, cumidine, and amidotetra- and amidopenta-methylbenzene. 

The second class comprises those bases which yield no magenta on oxidation with arsenic acid, but do so if oxidised in presence of a base of the first class. These bases are aniline, orthotoluidine, and y-metaxylidine. The bases of the third class, metatoluidine and yS-metaxylidine, do not yield magenta under any conditions. 

The commercial dyestuff is the hydrochloride of rosanilinc the acetate, however, is also sometimes met with. The free base is also prepared for the manufacture of aniline blue. 

Free rosaniline crystallises in colourless leaflets, which become red on exposure to the air. It is sparingly soluble in cold water, somewhat more easily in hot water, and still more easily in alcohol. It is sparingly soluble in ether. 

---

SchifT s reagent A solution of rosaniline in water decolorized with sulphurous acid. Aliphatic aldehydes and aldose sugars give a magenta colour with this reagent with aromatic aldehydes and aliphatic ketones the colour develops more slowly aromatic ketones do not react. 

The triaryknethane dyes are broadly classified into the triphenyknethanes (Cl 42000—43875), diphenylnaphthyknethanes (Cl 44000—44100), and miscellaneous triphenylmethane derivatives (Cl 44500—44535). The triphenyknethanes are classified further on the basis of substitution in the aromatic nuclei, as follows (/) diamino derivatives of triphenylmethane, ie, dyes of the malachite green series (Cl 42000—42175) (2) triamino derivatives of triphenylmethane, ie, dyes of the fuchsine, rosaniline, or magenta series (Cl 42500—42800) (J) aminohydroxy derivatives of triphenylmethane (Cl 43500—43570) and (4) hydroxy derivatives of triphenylmethane, ie, dyes of the rosoHc acid series (Cl 43800—43875). Monoaminotriphenyknethanes are known but they are not included in the classification because they have Httie value as dyes. 

Rosaniline or magenta was originally obtained by oxidising with arsenic acid a mixture of aniline with 0- and />-toluidine. The product was then lixiviated and treated with common salt, which converted the ai senate into the hydrochloride of rosaniline. Pararosaniline was prepared in a similar way fiom a niixtuie of aniline and /-toluidine. The series... 

Benzaldehyde reacts with many chemicals in a marked manner (1) with aramomo-silver nitrate ( Tollen s solution ) to form metallic silver, either as a black precipitate or as an adherent mirror film on glass (but does not reduce alkaline cupric solution. Fehling s solution ) (2) with rosaniline (fuchsine, magenta) that has been decolorized by sulfurous acid ( Schitf s... 

The rosaniline dye first obtained was probably a mixture of salts of both para-rosaniline and rosaniline. The names given to it at the beginning, viz., fuchsin and magenta, are still used. Acid fuchsin, a common form of the dye, is a mixture of the sodium salts of the mono-and di-sulphonic acid derivatives of para-rosaniline and rosaniline. 

Despite the economic importance of rosaniline (aniline red, magenta) (6) and its derivatives during the 1860s and after, there was no clear structural information about aniline-derived colorants, at least until 1878. Then, through the joint work of the cousins Emil and Otto Fischer, the search for the parent compound of 6 was successfully concluded with publication of the modern structures for aniline dyes. The Fischers starting point had been Caro and Wanklyn s work on 6 and rosolic acid (13). 

Fuschin (Magenta I) See rosaniline hydrochloride in Aromatic Compounds , Chapter 4,... 

Rosaniline is the color-base of magenta. The hydrochloride of the base is generally called magenta or fuchsine, although the acetate is also used under these names. Rosaniline is manufactured by ojddizing a mixture of aniline, o-toluidine, and p-toluidine, with arsenic acid, mercuric nitrate, or nitrobenzene. The reaction is analogous to that which takes place in the preparation of pararosaniline, of which rosaniline is a methyl derivative with the structure indicated by the following formula —... 

Acid magenta, or fuchsin S, is the sodium salt of the trisulphonic acid obtained by heating rosaniline with fuming sulphuric acid. 

Schiff s reagent is an aqueous solution formed by combining p-rosaniline hydrochloride (basic fuchsin), sodium bisulfite, and concentrated hydrochloric acid (Eq. 25.10). The reagent reacts with aldehydes to produce an imine, also called a Schiff base, that is magenta or purple in color (Eq. 25.11). The mechanism for forming the addition product presumably involves nucleophilic attack of sulfur on the aldehydic carbonyl group. 

---