Vat dyeing

It is used in the dispersed form as a dye for acetate silk, though it has no affinity for other fibres. It is also used as a starting point for alkyl- or acyl-aminoanlhraquinones which are used either as vat dyes or, after sulphona-tion, as acid wool dyes. 

It has been used as a bird repellant and is the parent compound of the anthraquinone vat dyes in which the dyeing is carried out by immersion in the reduced vat solution followed by air oxidation to the original insoluble compound. 

It is a valuable dyestuffs intermediate. When fused with KOH, two molecules of benz-anthrone combine at the positions marked above to give a dibenzanthrone which is in itself a vat dye. Also used as an intermediate for the preparation of the valuable Caledon Jade Green. 

ZnS204. Made SO2 on aqueous suspension of Zn dust. Used in bleaches and the vat dyeing process. 

As a 1.7 dtex (1.5 den) fiber, it can be spun into yams with a better strength conversion factor than other ceUulosics, aUowing rotor-spun Tencel to outperform ring-spun cotton or modal viscose. Fabrics can be made at high efficiency, and prove to have the anticipated tear and tensUe advantages over other ceUulosics. Direct, reactive, or vat dyes can be used, and easy care properties can be achieved with less resin finish than normal. Tencel could therefore be positioned as a new premium quaUty apparel ceUulosic and not simply as a long-term replacement for viscose. 

Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

The inorganic reductions of NaBH are numerous and varied (Table 7). Comparatively few anions are reduced, yet the reduction of bisulfite to dithionite (hydrosulfite) (25), which is used in the pulp (qv) and paper (qv), clay (see Clays), and vat dyeing industries, is an important inorganic appHcation ofNaBH,. 

Uses. The principal uses of NaBH are ia synthesis of pharmaceuticals (qv) and fine organic chemicals removal of trace impurities from bulk organic chemicals wood-pulp bleaching, clay leaching, and vat-dye reductions and removal and recovery of trace metals from plant effluents. 

The dianhydride of 1,4,5,8-naphthalene tetracarboxyhc acid [81-30-1] has been of research interest for the preparation of high temperature polymers, ie, polyimides. The condensation of the dianhydride with o-phenylenediamines gives vat dyes and pigments of the benzimidazole type. 

Amino-l-naphthalenecarboxyhc acid can be converted, by dia2oti2ation and treatment with ammoniacal cuprous oxide, to l,l -binaphthalene-8,8 -dicarboxyhc acid [29878-91-9] (48). Treatment of (48) with concentrated sulfuric acid yields anthranthrone. The dihalogenated anthranthrones are valuable vat dyes. 

Approximately 90% of the phthalocyanines (predominantly copper phthalocyanine) are used as pigments (qv). In addition, they have found acceptance in many types of dyestuffs, eg, direct and reactive dyes, water-soluble and solvent-soluble dyes with physical and chemical binding, a2o-reactive dyes, a2o nonreactive dyes, sulfur dyes, and vat dyes (1) (see Dyes Dyes, reactive). 

Dyes, Dye Intermediates, and Naphthalene. Several thousand different synthetic dyes are known, having a total worldwide consumption of 298 million kg/yr (see Dyes AND dye intermediates). Many dyes contain some form of sulfonate as —SO H, —SO Na, or —SO2NH2. Acid dyes, solvent dyes, basic dyes, disperse dyes, fiber-reactive dyes, and vat dyes can have one or more sulfonic acid groups incorporated into their molecular stmcture. The raw materials used for the manufacture of dyes are mainly aromatic hydrocarbons (67—74) and include ben2ene, toluene, naphthalene, anthracene, pyrene, phenol (qv), pyridine, and carba2ole. Anthraquinone sulfonic acid is an important dye intermediate and is prepared by sulfonation of anthraquinone using sulfur trioxide and sulfuric acid. 

Addition of sodium dithionite to formaldehyde yields the sodium salt of hydroxymethanesulfinic acid [79-25-4] H0CH2S02Na, which retains the useful reducing character of the sodium dithionite although somewhat attenuated in reactivity. The most important organic chemistry of sodium dithionite involves its use in reducing dyes, eg, anthraquinone vat dyes, sulfur dyes, and indigo, to their soluble leuco forms (see Dyes, anthraquinone). Dithionite can reduce various chromophores that are not reduced by sulfite. Dithionite can be used for the reduction of aldehydes and ketones to alcohols (348). Quantitative studies have been made of the reduction potential of dithionite as a function of pH and the concentration of other salts (349,350). 

Sulfurized V tDyes. These dyes occupy an intermediate position between the tme vat colors and sulfur dyes because, like vat dyes, they are dyed preferentially from a sodium dithionite—caustic soda bath. However, some dyes of this class can also be dyed from an alkaU sulfide bath or a combination of the two, depending on the dyeing method used and the nature of the substrate to be dyed. This has led to some confusion because Cl Vat Blue 42 and 43 are Hsted in the constitution section of the Colourindex under sulfur dyes. Although inferior to tme vat dyes in fastness properties, they offer the advantage of better fastness, especially to chlorine, than conventional sulfur dyes. 

In dyehouses where sulfide effluent is a problem, sulfur dyes of good chlorine fastness that dye satisfactorily from a dithionite—caustic alkaU bath offer an advantage. Included in this group are Cl Sulfur Black 11, Cl Sulfur Red 10 [1326-96-1] (Cl 53228), Cl Sulfur Brown 96 [1326-96-1] (Cl 53228), Cl Vat Blue 42, and Cl Vat Blue 43. The shades of these dyes can be brightened by the addition of vat dyes thus increasing the fastness of the resulting dye. 

The stmcture of the sulfuri2ed vat dyes is uncertain but in the presence of amino or methyl groups, thia2o1e-ring formation is possible. Examples have been confined to the dyes whose intermediates have been subjected to the conventional sulfur or polysulfide bake (Tables 2—5). 

Sulfur dyes are appHed to leuco form. In this form, the dye has affinity for the fiber. After the dye is completely absorbed by the fiber, it is reoxidized in situ. In dyes, such as the bright blues which contain quinonimine groups, further reduction takes place in a manner similar to the reduction of the keto group in vat dyes. 

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