Several examples are used to show that the reactivity of dichloro-and trichloropyrimidyl dyes and the sensitivity of their dyeings to hydrolysis are determined by the nature of the bridge unit between the chromophore and the reactive system. The tendency of the dyeings to hydrolyze in acid and, more particularly, in alkaline media increases with increasing reactivity of the dyes. In alkaline media, dyeings made with dyes containing oxygen bridges are cleaved mainly between the reactive system and the chromophore, while in dyeings made with dyes containing imino or methylimino bridges, the linkage between the reactive system and the cellulose is hydrolyzed.
Reactive dyes are those that react with a textile substrate with formation of a homopolar bond. In 1956, I.C.I. introduced the Procions@, the first reactive dyes for cellulose. Reactive dyes for wool (Remalan@ and Cibalan Brilliant @ dyes) had appeared earlier. However, the rapid development of this class of dyes, which is still in full swing today, came into effect only after the appearance of the Procions@, Advances have also been made in the application of reactive dyes to other textile substrates. As a result of this research the Procinyl@ dyes, a class of reactive disperse dyes for polyamide fibers, and others, were created. At the present time, however, reactive dyes for cellulose claim the greatest interest. The success of the reactive dyes for cellulose fibers is chiefly due to the brilliance and high wet fastness properties of their dyeings. The brilliance of reactive dyeings, which often cannot be matched by dyes of other classes, is due to the uncomplicated, narrow absorption bands displayed by the simple structure of the dye molecules, while the good wet fastness is the result of the stable linkage between the dye and the 14) A.