Indigosols

water-soluble salts of acid sulfate esters of leuco compounds of vat dyes. (The Soviet term is kubozol’)

The indigosol industry first developed in Switzerland in the 1920’s. There are many trade names for indigosols’for example, Anthrasol, tinozols, and Chelasol. Since 1924 indigosols have been prepared through the reaction of metal powder (iron, zinc, or copper), a vat dye, and chlorosulfonic acid in a basic, anhydrous organic medium. The resulting intermediate products dissociate under the action of a soda solution, the base is distilled off, the ferric oxides are filtered out, and the residue is subsequently salted out and dessicated. The mechanism involved in this process has not yet been thoroughly clarified.

Indigosols dissociate rapidly upon exposure to light, heating, or the action of acids; the commercial products are stabilized with special additives (urea, urotropin, or alkalies). Indigosols are used in dyeing vegetable fibers, as well as certain synthetic fibers, wool, natural silk, and rayon. In smooth dyeing, the fabric is impregnated with a weakly alkaline or neutral indigosol solution, and an insoluble dye is then precipitated onto the fabric by the action of an acidulated oxidant solution. This treatment makes it possible to achieve evenness in very slight dyeing, as well as deep staining of very thick fabric.