Types and Mode of Reaction

Sulfur dyes contain in their molecule S-S bridges. For technical and applicatory reasons, sulfur dyes are available in various modifications, which are classified in the Colour Index under the general generic names  

Sulfur Dyes (C.I. Sulphur). Two types of sulfur dyes exist amorphous powders, which are insoluble or partially soluble in water. They must be brought into solution by reduction with sodium sulfide, according to Equation (5). 

With polysulfide melt dyes (i.e., quinoneimine sulfur dyes), the reducing agent can attack not only the disulfide groups but also the quinoneimine group (as in the case of vat dyes). Dispersible pigments are used particularly for pad dyeing. 

The dispersible, partly reduced pigments bearing the name Sol contain a dispersant and a certain amount of reducing agent. 

Leuco Sulfur Dyes (C.I. Leuco Sulphur). These liquid dyes already contain the reducing agent required for dyeing. They must simply be diluted with water before application. Ecologically more favorable, low-sulfide types have come onto the market recently. 

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