Dyes for wool

Hydrolysis of ester groups can also occur in certain wool dyes. For example, Cl Acid Red 1 (3.26) loses its acetyl group (Scheme 3.5) on prolonged dyeing in an acid dyebath, the hue becoming bluer and duller and the dyeing much less fast to light. 

A previously much used red wool dye is C.I. Acid Red 14 (see Section 3.9.3), which is now used to a limited extent in wool dyeing for inexpensive articles. 

Aniline black in substance is scarcely ever prepared in the colour manufactory, but is always produced directly on the fibre. It lias an extended application in calico-printing and cottondyeing, but as yet is of little service in wool-dyeing. For aniline-black printing innumerable recipes have been published and patents taken, all depending on one or other of the methods of formation mentioned in the introduction to this chapter. 

Uses Dye for prod, of inks, carbon paper coatings, for dyeing natural fibers such as jute, sisal, wool dye for prod, of daylight fluorescent pigments and gloss paints in paints, varnishes colorant for seeds and crop protection agents... 

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. 

Picric Acid and Ammonium Picrate. Picric acid (PA) (2,4,6,-trinitrophenol) was the first modem high explosive to be used extensively as a burster ia gun projectiles. It was first obtained by nitration of iadigo, and used primarily as a fast dye for silk and wool. It offered many advantages when compressed, it was used as a booster for other explosives, and when cast (melting poiat 122.5°C) served as a burster ia shell it was stable, iasensitive, nonhygroscopic, relatively nontoxic, and of high density when cast, and could be made economically by simple nitration. 

Various methods of home-dyeing cotton and wool materials using natural dyes made from hulls of butternut, hickory nut, pecan, eastern black walnut, and Knglish walnut have been described (149). As far back as during the Civil War, butternut hulls have been used to furnish the yellow dye for uniforms of the Confederate troops. More recent attempts have been made to manufacture yellow and brown dyes from filbert shells on a commercial scale. The hulls are treated with copper sulfate and concentrated nitric acid to produce a yellow color, with ferrous sulfate to produce oHve-green, or with ammonia to produce mby-red (150) (see Dyes AND DYE INTERMEDIATES Dyes, natural). 

Chromium is the principal metal used with mordant dyes for wool, whereas both chromium and cobalt are used extensively ia premetallized types for wool and nylon. Copper(II) is employed almost exclusively as the chelating metal ion ia both metaUizable and premetallized direct dyes for cotton. 

Subsequendy, H. Caro and W. H. Perkin independendy developed the commercial manufacturing process of alizarin from anthraquinone (qv) through anthraquinone-2-sulfonic acid. Taking advantage of these inventions, many manufacturers came to produce various kinds of hydroxyanthraquinones, which were used as mordant dyes for dyeing cotton and wool. 

A variety of derivatives have been produced from alizarin and used as mordant dyes for cotton and wool. Examples are given in Table 7. 

Wool—Acrylic Fibers. This blend is being used for iadustrial and hand knitting yams. The acryHc fiber is aesthetically similar to wool, iacreases the strength of the yam, and adds bulk to the goods. Special precautions are necessary siace the two fibers are colored with dyes of opposite ionic type. Coprecipitation is prevented with the use of an antiprecipitant. Usually, level dyeing acid dyes are used for the wool portion in combination with the cationic dyes for acryHc fiber. 

Wool—Polyester Fibers. The 45/55 wool—polyester blend is the most common fiber combination in the worsted industry. Strength and exceUent dimensional stabiHty of the polyester fiber enable the creation of lightweight wear fabrics not obtainable before. Economy has modified the fiber ratio and 30/70 and 20/80 wool—polyester blends are as common as the classical 45/55 blend. Disperse dyes for polyester and acid or neutral premetaUized dyes for wool are employed in a one-bath process. Should cationic dyes be used for the wool portion, a one-bath procedure can only be employed for light to medium shades, whereas dark shades require a one-bath two-step process. Wool blends should not be dyed above 105°C in order to avoid deterioration of the fiber quaHty. 

Copper and chromium are used for complexing a number of dyes such as the coppered direct and reactive dyes for cotton and metaUi2ed and neutral metal complex acid dyes for nylon, wool, etc. Examples are Direct Blue 218 [28407-37-6] (Cl 24401) (317), Reactive Violet 2 [8063-57-8] (Cl 18157) (318), and Acid Black 52 [5610-64-0] (Cl 15711) (319). 

T artrazine, 4,5-dihydro-5 -oxo-1 -(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-1// -pyrazole-3-carboxylic acid trisodium salt was discovered by Ziegler in 1884 and is used as a dye for wool and silk. It is used as a colour additive in foods, drugs and cosmetics, and is an adsorption-elution indicator for chloride estimations in biochemistry (B-76MI40404). 

According to Urbanski (Ref 35. p 473) In the second half of the nineteenth century, Picric Acid was very widely used as a fast dye for silk and wool. The first definite suggestions as to the application of Picric Acid for the manufacture of explosives go back to the early second half of the nineteenth century. They referred... 

Triphenylmethane leuco dyes are far more important than the diphenylmethanes in terms of practical value. Use of triphenylmethane dyes for traditional applications of dyes is limited to dyeing wool, silk, leather, and polyacrylonitrile fibers. The largest portion of the annual production of this class of leuco dyes is consumed in the manufacturing of various copying papers. 

There is a wide diversity of chemical structures of anthraquinone colorants. Many anthraquinone dyes are found in nature, perhaps the best known being alizarin, 1,2-dihydroxyanthraquinone, the principal constituent of madder (see Chapter 1). These natural anthraquinone dyes are no longer of significant commercial importance. Many of the current commercial range of synthetic anthraquinone dyes are simply substituted derivatives of the anthraquinone system. For example, a number of the most important red and blue disperse dyes for application to polyester fibres are simple non-ionic anthraquinone molecules, containing substituents such as amino, hydroxy and methoxy, and a number of sul-fonated derivatives are commonly used as acid dyes for wool. 

Mordant dyes generally have the characteristics of acid dyes but with the ability in addition to form a stable complex with chromium. Most commonly, this takes the form of two hydroxy groups on either side of (ortho to) the azo group of a monoazo dye, as illustrated for the case of C. I. Mordant Black 1 (151). The dye is generally applied to the fibre as an acid dye and then treated with a source of chromium, commonly sodium or potassium dichromate. As a result of the process, the chromium(vi) is reduced by functional groups on the wool fibre, for example the cysteine thiol groups, and a chromium(m) complex of the dye is formed within the... 

There are relatively few other reactive groups which react by nucleophilic addition and which have achieved significant commercial success. However, one particular system which is worthy of note is the a-bromoacrylamido group, found in the Lanasol dyes (Ciba), which are among the most widely used reactive dyes for wool. The chemistry... 

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