Indigoid vat dyes

Isatin is the inner anhydride (lactam) of a y-amino-a-ketocarboxylic acid, isatinic acid (A), and is converted into a salt of this acid by the action of alkali. The keto-group in position 3 can condense with many other substances, and for this reason isatin is manufactured on a technical scale and converted into valuable indigoid vat dyes. The magnificent thioindigo scarlet, which is obtained from isatin and a sulphur analogue of indoxyl (the so-called hydroxythionaphthene), may be taken as example qq... 

Indigoid vat dyes are derivatives of indigo and thioindigo (see Section 3.5). Leucoindigo compounds have a comparatively low affinity for fibers. Thus, these dyes are used mainly in textile printing rather than dyeing (see Section 4.4.6). 

The leuco esters of vat dyes are anthraquinoid or indigoid vat dyes (Section 3.4) that have been made water soluble by reduction and esterification of the hydroxyl groups with sulfuric acid. These dyes are used mainly for dyeing high-quality articles of cellulose fibers in light colors and polyester-cellulose blends to moderate depths of shade [58], [59, p. 568],... 

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