Leather Sulfur Dyes

Phthalocyanine Dyes. In addition to their use as pigments, the phthalocyanines have found widespread appHcation as dyestuffs, eg, direct and reactive dyes, water-soluble dyes with physical or chemical binding, solvent-soluble dyes with physical or chemical binding, a2o reactive dyes, a2o nonreactive dyes, sulfur dyes, and wet dyes. The first phthalocyanine dyes were used in the early 1930s to dye textiles like cotton (qv). The water-soluble forms Hke sodium salts of copper phthalocyanine disulfonic acid. Direct Blue 86 [1330-38-7] (Cl 74180), Direct Blue 87 [1330-39-8] (Cl 74200), Acid Blue 249 [36485-85-5] (Cl 74220), and their derivatives are used to dye natural and synthetic textiles (qv), paper, and leather (qv). The sodium salt of cobalt phthalocyanine, ie. Vat Blue 29 [1328-50-3] (Cl 74140) is mostly appHed to ceUulose fibers (qv). 

The H2S sulfanes are the subject of several reviews (129,133). Except for hydrogen sulfide these have no practical utiUty. Sodium tetrasulfide [12034-39-8] is available commercially as a 40 wt % aqueous solution and is used to dehair hides in taimeries, as an ore flotation agent, in the preparation of sulfur dyes (qv), and for metal sulfide finishes (see Leather Mineral recovery and processing). 

Sulfur dyes are used mainly for dyeing textile ceUulosic materials or blends of ceUulosic fibers (qv) with synthetic fibers such as acryUc fibers, polyamides (nylons), and polyesters. They are also used for sHk (qv) and paper (qv) in limited quantities for specific appHcations. Solubilized sulfur dyes are used on certain types of leathers (qv). 

Sulfur dyes of the Indocarbon type (C.I. Sulphur Black 6, 53295 [1327-16-8], C.I. Sulphur Black 7, 53300 [1327-17-9] and C.I. Sulphur Black 11, 53290 [1327-14-6]) are also used for printing on these fibers. Sulfur dyes find limited use with polyamide fibers, silk, leather, paper, and wood. 

Basic dyes are used almost exclusively for overdyeing, e g., to achieve deep black shades by laking. Recent research indicates that new cationized sulfur dyes for leather will shortly become commercial products. In the 1970s dicationic azo dyes for paper were introduced by azo coupling of aromatic diazonium ions with heterocylic components. The resulting cationic azo dyes are also applied on leather e.g. C.I. Basic Black 11. The constitution is not disclosed. 

Initially, sulfur dyes were water-insoluble, macromolecular, colored compounds formed by treating aromatic amines and aminophenols with sulfur and/or sodium polysulfide. R. Vidal developed these dyes in 1893 but they only became attractive for leather with the introduction of water-solubilizing groups. Today, the sulfur dyes can be divided into three classes conventional water-insoluble, leuco, and solubilized sulfur dyes. Most sulfur dyes are synthesized by condensation of aromatic amines with sulfur or sodium polysulfide in the so-called bake process, or else in water or under pressure as a solvent-reflux reaction. 

Many sulfur dyes contain benzothiazole, thiazone or thianthrene groups, and almost the whole range of shades can be obtained. The number of commercially available sulfur dyes is small but their production volume is large. Sulfur Black T with all conceivable variations may be the biggest synthetic dye which is used as a penetrating dye on leather Sulphur Black 1, 53185 [1326-82-5] (18 most probable structure). 

This dye is not commercialized for leather however, recent research and development have produced a true azo-sulfur hybrid and also cationized sulfur dyes for leather. These dyes will shortly become commercial products. 

Sulfur dyes are eminently suitable for through-dyeing leather, and because of the recent upsurge in demand for such leather this class of dyes has experienced a renaissance. In spite of numerous advantages, ecological problems regarding sulfur byproducts have to be taken into account by the manufacturer of these dyes and by tanneries applying them on leather. 

Uses Dye intermediate for azo and sulfur dyes colorant in hair dyes dyeing furs, leather pharmaceuticals... 

The practical route for oxidizing leuco diphenylmethanes 15 demands inital conversion to an imine salt 16. The imine salt is obtained by heating a mixture of diphenylmethane, sulfur, ammonium chloride, and sodium chloride at 175°C in a current of ammonia or by heating a mixture of diphenylmethane, urea, sulfamic acid, sulfur, and ammonia at 175°C (Scheme 3). Dyes 16 can be represented as the quinonoid resonance structure 17. Dyes of this class, known as auramines, are all yellow, with the only commercial representative being auramine O 16a. Due to its poor lightfastness and instability to hot acids and bases, its use has been restricted to dyeing and printing cotton, paper, silk, leather, and jute. 

The most important leather dyes identified by typical chemical nomenclature are azo, stilbene, triaiylmethane, quinoline, azine, oxazine, thiazine, sulfur, and phthalocyanine. 

Hydrolysed, polynuclear Cr complexes are of considerable commercial importance in the dying and tanning industries. In the former the role is that of a mordant to the dye. In leather production it is necessai to treat animat hides to prevent putrefaction and to render them supple when dry. Traditionally, tannin was used, hence the name of the process, but this was superseded towards the end of the nineteenth century by solutions of chromium(lil) sulfate. After soaking in sulfuric acid the hides are impregnated with the Cr solution. This is subsequently made alkaline, when the polynuclear complexes form and bridge... 

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