Sulphatoethyl-sulphone and -sulphonamide Dyes

The Remazol (HOE) vinylsulphone dyes, containing the characteristic 2- sulphatoethylsulphonyl precursor grouping, are intermediate in reactivity between the high-reactivity heterocyclic systems, such as dichlorotriazine or difluoropyrimidine, and the low-reactivity ranges, such as aminochlorotriazine or trichloropyrimidine. Exhaust dyeing temperatures between 40 and 60°C may be chosen, depending on pH, since caustic soda is often selected to bring about alkaline hydrolysis of the precursor sulphate ester. These dyes are applicable by a wide variety of batchwise and continuous processes. The substantivity of many of these dyes is markedly lower than that of typical haloheterocyclic dyes. Not only has the vinylsulphone group, unlike the heterocyclic ring systems, little if any inherent affinity for cellulose, but the terminal sulphato group enhances the aqueous solubility of the precursor form before 1,2-elimination to the vinylsulphone. In contrast to the haloheterocyclic systems, the dye–fibre bonds formed by the vinylsulphone dyes are at their weakest under alkaline conditions.

For three decades the two most widely used reactive dyes have been those illustrated in Figure : Remazol Black B and Remazol Brilliant Blue R. The four solubilising groups in the precursor form of CI Reactive Black 5 confer high solubility but unusually low substantivity. It is a nearly symmetrical bis(sulphatoethylsulphone) structure and as these precursor groups lose their ionic charge by 1,2-elimination, the substantivity for cellulose is enhanced and the bis(vinylsulphone) structure formed shows excellent fixation efficiency under alkaline conditions. After fixation the inherently low substantivity of the unfixed bis(hydroxyethylsulphone) dye makes washing-off easy in a region of the colour gamut where this is often notoriously difficult.

CI Reactive Blue 19

The extremely attractive bright blue hue combined with excellent light fastness of CI Reactive Blue 19 could not be challenged by other reactive blue dyes for many years. The aqueous solubility of this dye is inherently low and depends on the zwitterionic 1-amino-2-sulpho grouping after 1,2-elimination of the sulphate ester has taken place. This has led to poor reproducibility and levelling problems, but nevertheless this dye has remained second only to Black 5 in terms of market share amongst reactive dyes.

In a recent investigation of the effect of low-frequency ultrasonic waves on the stability of the copper-complex phenylazo H acid dye Remazol Brilliant Violet 5R (Figure 4.8), reaction rates were recorded for the 1,2-elimination of the sulphato group to form the vinylsulphone and for hydrolysis of the latter to form the 2-hydroxyethylsulphone.

Certain members of the Hoechst range are designated Remazol D brands and these contain a 2-sulphatoethylsulphonamide precursor grouping formed by reacting the dye base with carbyl sulphate . As in the case of the conventional vinylsulphone types, 1,2-elimination occurs under alkaline conditions to give the reactive vinylsulphonamide group and this is capable of either reaction with cellulose or hydrolysis to the hydroxyethylsulphonamide according to the usual nucleophilic addition mechanism.