Polysulfide Melt Dyes

The starting products for reflux thionation in aqueous or solvent media are chiefly derivatives of indophenol (10, Y = OH) and indoaniline (10, Y = NH2). The starting compounds are often in the leuco form 11. 

This class of compounds also includes phcnazone, phenothiazone, and phe-noxazone derivatives (12), and so these polysulfide melt dyes are also referred to as quinoneimine or indophenol sulfur dyes. 

Gnehm and Kaufler [4] showed that C.I. Sulphur Blue 9, 53430 [1327-56-6], which is prepared by sulfurization of the indophenol derivative 10 [Y = N(CH3)2], has the phenothiazone structure 12. 

In this way it was established that both thiazone and thianthrene structures are present in all the quinoneimine sulfur dyes studied (C.L. Vat Blue 43, 53630 [1327-79-3] C.L Sulphur Black 6, 53295 [1327-16-8], C.l. Sulphur Black 7, 53300 [1327-17-9]-, C.L Sulphur Black 11, 53290 1327-14-6] and C.L. Sulphur Red 5, 53820). The thianthrene structure was also found to contribute greatly to the sub-stantivity of the dyes. 

Polysulfide melt dyes, which are applied chiefly with dithionite and commonly show a higher degree of fastness, are called sulfur vat dyes. They include such dyes as C.I. Vat Blue 43 and C.I. Sulphur Black 11. 

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Sulfur dyes are a special class of dyes with regard to both preparation and application, and knowledge of their chemical constitution [1], They are made by heating aromatic or heterocyclic compounds with sulfur or species that release sulfur. Sulfur dyes are classified by method of preparation as sulfur bake, polysulfide bake, and polysulfide melt dyes. Sulfur dyes are not well-defined chemical compounds but mixtures of structurally similar compounds, most of which contain various amounts of both heterocyclic and thiophenolic sulfur. 

The structure 15 can thus be regarded as the prototype of the polysulfide-melt dyes (quinoneimine or indophenol sulfur dyes) (Scheme 2.8). 

Tables 3.9 and 3.10 present some examples of the preparation of polysulfide-melt dyes.

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 leuco form is absorbed by the substrate and then oxidized to the insoluble dye. Since several mercapto groups are present per dye molecule, oxidation causes not only dimerization but also cross-linking of dye monomers . For polysulfide melt dyes, the quinonimine group is also involved in the reaction. This is apparent in the change in shade that occurs during reduction. 

Polysulfide Melt. Cl Sulfur Black 1 [1326-82-5] (Cl 53185), derived from 2,4-dinitrophenol, is the most important dye in this group which also includes the indophenol-type intermediates. The latter are appHed in the stable leuco form. The derived dyes are usually confined to violet, blue, and green shades. Other members of this group are intermediates capable of forming quinoneimine (10) or phenazone stmctures (11) that produce red-brown or Bordeaux shades ... 

Liquids. Some Hquid dyes are made directly from the thionation melt by additions of caustic soda and sodium hydrosulfide. Hydrotropic substances are sometimes added, either at the initial thionation stage or after the polysulfide melt is finished in order to keep the reduced dye in solution. Pardy reduced Hquids are also available. They are usually more concentrated than fully reduced Hquids, thus saving packaging and transportation costs. However, they require a further addition of reducing agent to the dyebath in order to obtain full color value. On the other hand, fully reduced Hquids are... 

The characteristic properties of Polysulfide Melt (Chinonimin-) Dyes can be expressed to a large extent in a simplified model (see Scheme 2.8, p. 83). 

The polysulfide melt process yields mainly reddish brown, violet, blue, green, and black sulfur dyes, depending on the intermediate. 

In this process, the reaction of the intermediates-essentially indophenols, chiefly in leuco form, or indophenol-like substances-with sulfur is effected by heating with alkali metal polysulfide in an aqueous or alcoholic medium under reflux. When monoethers of ethylene glycol or diethylene glycol (such as Carbitol) are used, the dye can be obtained in solution form after melting, without distillation and elimination of the solvent. Accordingly, these solvents are used chiefly in the preparation of ready-to-dye sulfur dye solutions. The addition of hydrotropic substances such as sodium xylenesulfonate improves the homogeneity of the melt and hinders sedimentation of the dye on storage. 

Table 3.9 Sulfur dyes made by polysulfide reflux melting in aqueous medium [3]... 

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