Condensation Dyes

Condensation dyes from 4-nitrotoluene-2-sulfonic acid are the most important of the stilbene dyes. Direct YeUow 11 (Cl 40000), discovered in 1883 and commonly known as Sun YeUow [1325-37-7] is widely used in the paper industry (2,4). 

Condensation dyes are produced by condensation of nitro compounds with amines... 

Table 3.1 (3.3.6.5) shows further examples of condensation dyes obtained from the corresponding aminoazo compounds and 4.4 -dinitrostilbcne- 2,2 -disul-fonic acid. 

As in the case of the metal-free direct dyes, a large diversity of structures is encountered here, too, there are direct dyes with pyrazolones, substituted 4,4 -diphenylamines, or the 1,3,5-triazine ring, urea and stilbene derivatives, and condensation dyes. 

Table 3.3 Examples of condensation dyes made from aminoazo compounds and 4,4 -dini-tro-stilbene-2,2 -disulfonic acid...

Isatin is used as such in the preparation of many valuable vat dyes. Still more important are the vat dyes prepiuea directly from a-isatinanilide by condensation with -hydroxythionaphthenes. As first observed by G. Engi, isatin and a-isatin-anilide lead to different dyes on condensation. In the case of isatin itself, the p group is reactive in the condensation reaction, while with a-isatinanilide, aniline is split out and o condensed dyes are formed. These a condensation products are much.more valuable as dyes than the isomeric p compounds. 

Aerofix N. [Aerochem] Aromatic condensate dye fixing agent for acid dyes on nylon. 

Maekawa, Y. Semicontinuously producing aniline condensed dyes. U.S. Patent 4056530, 1977 Chem. 

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