Dry leuco sulphur dyes in particulate form

Abstract

By reducing a sulphur dye (S) in aqueous medium with a reducing carbonyl compound in the presence of alkali metal hydroxide and optionally alkali metal (bi)sulphite at temperatures above 60.degree. C. and drying the reaction mixture, there are obtained very stable leuco sulphur dyes (L), which are practically free of sulphides and polysulphides, are readily and completely soluble in water and are usable for the dyeing of substrates dyeable with sulphur dyes, by which a disturbing development of H.sub.2 S or a disturbing inorganic sulphide occurrance in the waste water can be efficiently avoided; by spray-drying in a drying time <4 minutes as described there are obtained sulphide-free, stable leuco sulphur dyes (L) readily soluble in water and particularly suitable for sulphide-free dyeing, in particular for the dyeing of polyamidic fibrous substrates, especially of wool.