Acid Chrome Dyes

There are a number of different types of fiber that may be encountered and equally there are a number of different classes of dye, although some of these may only be associated with particular types of fiber. The type of fiber and the class of dye both affect the detailed scheme employed for the extraction of the dye from the fiber and the subsequent chromatographic analysis of the extract. A detailed discussion of the extraction schemes employed is beyond the scope of this text but, for example, acid dyes are best extracted using a mixture of pyridine and water (4 3 v/v), while reactive dyes require extraction with 1,2-diaminoethane at 90°C for 1 h. Schemes have been developed for the extraction of (1) acid-chrome dyes from wool (2) direct and reactive dyes from cellulosic fibers (3) azo dyes from... 

The dyes used on wool can be divided into the following groups acid dyes, chrome dyes, premetallized dyes and reactive dyes (88,89,92—94,97—99). Strictly speaking, all types of wool dyestuffs can be described as acid dyes, but in practice this term is confined to leveling acid dyes, half-milling dyes, milling dyes, and supermilling dyes (94,97). This subclassification of acid dyes arises out of the methods used for their appHcation and their fastness properties on wool. 

Chrome dyes are acid dyes (mol wt 300—600) that contain groups capable of forming complexes by reaction with a metal salt, usually sodium or potassium dichromate (94,97). The chrome/dye complex has lower solubiUty, and hence better wetfastness, than the parent dyestuff. Reaction between the... 

Mordant dyes are notoriously troublesome from the viewpoint of colour matching because the hue of the chromium complex usually differs greatly from that of the unmetallised parent dye (section 5.4.1). If other metal ions are present in the treatment bath or on the fibre during chroming, the colour obtained is likely to differ from that of the pure chromium complex. Certain important chrome dyes, including Cl Mordant Black 11 (3.29) and Black 17 (3.30), are particularly sensitive to traces of iron or copper. The hue of the black dyeings obtained is redder in the presence of copper and browner with iron contamination. The fastness to light and wet treatments may also prove inferior under these conditions. Even certain 1 2 metal-complex acid dyes show similar effects in the presence of these impurities,... 

Dichromate anions are readily absorbed under acidic conditions by wool that has been dyed with chrome dyes. The chromium(VI) on the fibre is then gradually reduced by the cystine residues in wool keratin to chromium(III) cations, which react with the dye ligands to form a stable complex. In this way the cystine disulphide bonds are destroyed, resulting in oxidative degradation of the wool fibres [71]. 

In spite of their long-recognised disadvantages, or as a result of the substantial efforts to overcome them, chrome dyes still represent about 30% of total dye consumption in wool dyeing (Table 3.10 in section 3.2.2). Premetallised acid dyes and reactive dyes for wool account for a further 40%, so it is not surprising that much attention has been given to... 

Dyes Resin-bonded pigment systems. Vat, acid, or chrome dyes will tint. Availahle from numerous manufacturers. 

Chrome dyes (see Section 3.11.2) are selected acid dyes that form complexes with chromium ions. With complex formation a strong bathochromic shift of shade occurs. In addition, as a result of the superposition of several excited states, a marked dulling of the hue is observed. 

Analogous Sulfonations. Exactly the same method can be used for sulfonating p-nitrochlorobenzene, p-nitrotoluene, o-m trochlorobenzene, chlorobenzene, and many other compounds. On the other hand, it is usually not possible to sulfonate dinitaro compounds in this way. Dinitrochlorobenzene and dinitrotoluene are decomposed explosively by treatment with fuming sulfuric acid. If dinitrochloro-benzenesulfoitic acid is to be prepared, for example, one starts with p-nitrochloro-benzene/ This is sulfonated, as described previously, and the sulfonic acid is converted to dinitrochlorobenzenesulfonic acid by treatment with mixed acid (50 50 sulfuric and nitric acids) at low temperatures. This product yields, on replacement of the chlorine by —OH and partial reduction, 4-nitro-2-aminophenol-6-sulfonic acid (nitro acid III), which is used in preparing chrome dyes. 

For dyeing wool, the water-insoluble material is dissolved in ammonia and the solution is made distinctly acid with acetic acid. The dye is after-chromed with sodium bichromate, making the shade fuller and completely fast to boiling. 

Picriunic acid has recently become very important as an azo dye component. Its (liazo compound, reacted with unsulfonated couplers, gives very fast chrome dyes for wool, characterized by the fact that they can be used with chromic acid in the dye bath. Exiunples are the metachrome dyes, e.g., metachrome brown ... 

In the dyeing of wool, REMOL GES Liquid is effective with neutral, acid, chrome and reactive dyestuffs, e.g. HOSTALAN dyestuffs. 

Use Dye for cotton, stain for microscopy, reagent for boron determination, manufacture of acid and chrome dyes. 

If a fibre sample can be dissolved in 5 % NaOH at the boil, it is a protein fibre, commonly wool or silk. Protein fibres can be dyed most often by acid dyes, metallised acid dyes and chrome dyes. According to the AATCC system, acid dyes on protein fibres can be identified as follows. A coloured sample is boiled in an ammonia solution for 1-2 min. After removing the coloured sample, the ammonia solution is slightly over-neutralised with sulphuric acid. A small piece of white wool sample is then redyed with the ammonia solution at the boil for 1-2 min. A positive indication of acid dyes on the original sample is evidenced by the colour of the redyed wool sample. If chrome dyes are on the dyed sample, no redyeing can... 

A naturally-occurring mordant dye, used extensively until a few years ago, and now probably the only one still in use, is logwood. It yields a navy blue or a black, with what is called a good bloom, when dyed on chrome mordanted wool. Until the advent of acid mordant dyes, which will be described later, it was the only dyestuff with which wool could be dj ed black with any measure of fastness. 

The acid mordant dyes are applied, in the first stage, in the manner already described for acid dyes. Because the exhaustion is not so good as with wool it is advisable to run the dye liquor off when the dyeing cycle is complete and refill with fresh water for chroming. The chroming is carried out with 3 to 4 per cent of formic acid (85 per cent) and the following quantities of dichromate ... 

In the case of the pale shades the two fibres can be dyed in the same liquor with a disperse and an acid milling or a premetallized dye, and subsequently cleared with permanganate in the manner described in the previous paragraph. With dark colours it is better to dye the polyester first then clear the wool with sodium hydrosulphite, ammonia, and a non-ionu dispersing agent, and finally match the protein fibre with acid or premetallized colours. It must be borne in mind that when after-chrome dyes art used, some disperse dyestuffs are modified by the dichromate, with change of colour. C.I. disperse red 11 (Cibacet Brilliant Pink 4BN) anc C.I. DISPERSE RED 15 (Duranol Red 2B) are particularly susceptible, anc C.I. DISPERSE RED 13 (Cibacet Rubine R) should be substituted. 

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