Colouration acid dyes

Some reference to the use of nitrous acid merits mention here. Primary aromatic amines yield diazonium compounds, which may be coupled with phenols to yield highly-coloured azo dyes (see Section IV,100,(iii)). Secondary aromatic amines afford nitroso compounds, which give Liebermann a nitroso reaction Section IV,100,(v). Tertiary aromatic amines, of the type of dimethylaniline, yield p-nitroso derivatives see Section IV,100,(vii). ... 

The three most important types of synthetic fibres used commonly as textiles are polyester, polyamides (nylon) and acrylic fibres. Polyester and the semi-synthetic fibre cellulose acetate are dyed almost exclusively with the use of disperse dyes. Polyamide fibres may be coloured using either acid dyes, the principles of which have been discussed in the section on protein fibres, or with disperse dyes. Acrylic fibres are dyed mainly using basic (cationic) dyes. 

Nitro dyes exhibit benzenoid-quinonoid tautomerism (1.25) and their colour is attributed mainly to the o-quinonoid form, since this can be stabilised by hydrogen bonding. The tautomeric o-nitrosonaphthols (1.26) readily form chelate complexes with metals. A few yellow nitro disperse dyes, including Cl Disperse Yellow 1 (1.25), and brown acid dyes remain of significance. The remaining nitro and nitroso colorants, such as (1.26) and its 1 3 iron (II) complex (1.27), are no longer of commercial interest. 

There is as yet no agreed international list of permitted food colours. Thus a food dye that is permitted in one country may be considered unacceptable in another. The synthetic food colorants permitted in the European Union are listed in Table 1.8 [60]. All were originally introduced as acid dyes for wool many years ago. Furthermore, more than thirty colorants of natural origin are permitted in most countries. The natural carotenoid dyes are of outstanding importance for colouring edible fats and oils. These yellow to red methine dye structures occur in many families of plants and animals, including vegetables, berries,... 

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,... 

Monosulphonated levelling acid dyes are mainly yellow or red in colour, whilst the larger molecular size that can be tolerated with a disulphonated milling acid dye allows the use of disazo compounds, such as Cl Acid Blue 118 (4.56), to cover more bathochromic hues such as navy blue. 

It was pointed out in Chapter 1 that, after the azo class, anthraquinone derivatives form the next most important group of organic colorants listed in the Colour Index. The major application groups are vat dyes, disperse dyes and acid dyes (Table 1.1). 

In 1871 Graebe and Liebermann discovered that alizarin (6.2) could be applied to wool by mordant dyeing after sulphonation to produce the 3-sulphonic acid (6.28). This dye is still listed in the latest revision of the Colour Index as a commercial product [11]. Although many sulphonated polyhydroxyanthraquinones have been examined, few remain in current use. Another, and more important, classic dye that continues in commercial use as an acid dye is Cl Acid Blue 45 (6.29). This dye was discovered in 1897 by Schmidt and can be made from anthrarufin (6.13) by disulphonation, subsequent dinitration and reduction. The dye gives an attractive blue on wool with good all-round fastness properties. 

The nucleophilic displacement of suitable para substituents in analogues of malachite green is used as a means of synthesis of some important acid dyes. For example, Cl Acid Blue 83 (6.176 R = H) is made by the aldehyde method, using 4-chlorobenzaldehyde and N-ethyl-N-(3-sulphobenzyl)aniline. The resulting leuco base is oxidised to the colour salt,... 

The nomenclature given for these componnds is a nniversally recognised system for the naming of dyestuffs devised by the Society of Dyers and Colourists as part of their Colour Index (Cl). The Cl Generic Name is made up of the application class, the hne and a nnmber. Acid dyes are nsed on wool and polyamide, direct dyes on cel-lulosic fibres, paper and leather, disperse dyes on polyester fibres, reactive dyes on cellnlosic fibres and basic dyes on polyacrylonitrile and paper. 

The colouring matter dyes wool in an acid bath the alcoholic or alkaline solution is usually fluorescent Phthaleins... 

A few dyes can be found in the Colour Index under the designation Fur . Five of them are acid dyes and some are oxidation dyes. These dyes are selected to dye the hair. However, an even larger number, including many mixtures, are suitable for dyeing fur hair. For dyeing suede almost the whole range of leather dyes are suitable (see Section 5.1). Nevertheless, they must be carefully selected in line with the desired requirements. 

One method of classifying acid dyes is to divide them into groups according to their application behavior. The traditional wool/nylon/cotton classification is customarily employed by the Colour Index and is therefore used here, too. 

Ratanathanawongs and Crouch [19] have described an on-line post-column reaction based on air-segmented continuous flow for the determination of phenol in natural waters by high performance liquid chromatography. The reaction used was the coupling of diazotised sulphanilic acid with the phenol to form high coloured azo dyes. The detection limit for phenol was 17pg L 1 which represents a 16-fold improvement over determination of phenol with ultraviolet detection. 

Afterfixing agent for improving the wet fastness properties of polyamide fibres dyed or printed with acid dyes. The light colour of this compound results in minimal effect on bright shades or white grounds of printed fabrics. Used to reserve polyamide when dyeing cotton/polyamide blends with direct dyes. 

S)-amino acicis, mexiule C, two stereoisomers, and tethered to polystyrene via mcxlule B, two stereoisomers) was prepared by encoded split synthesis on 100 pm polystyrene synthesis beads so that different library members were segregated on different beads (i.e. one bead, one chiral SO). This library was then screened by a two-colour differential binding method amino acid SAs were labelled via a linker with red ((/ )-amino acids) and blue ((S)-amino acids) dyes and the chiral beads treated with an equimolar mixture of the labelled SA enantiomers. Enantioselective binding beads are either red or blue, whereas unselective beads are brown. 

The property of dyeing belongs principally to compounds possessing a more or less marked acid or basic character. It is probable that these properties depend, at least in many cases, on a partly basic, partly acid character inherent in the fibre, which in the one case is developed by the colour-acid and in tjie other by the colour-base. 

As a rule animal fibres are not capable of decomposing the salts of acid dyestuffs, and in dyeing the colour-acids have to be set at liberty by the addition of a stronger acid to the dye-bath. Certain colour-acids, for example the sulphonic acids of amidoazo-compounds, have a different colour to that of their alkali salts. In dyeing wool with such colour-acids, the shade produced is that of f the salts and not that of the colour-acid, so that in such cases wool evidently plays the role of a base. 

Chryso idine, which was discovered by Witt, is one of the few basic azo-dyestuffs, and like all basic colouring-matters dyes cotton mordanted with tannic acid. Its principal application is in cottondyeing, especially for shading purposes. It gives a yellowish-orange colour. 

Anthragallol has a brown colour, and dyes brown shades on alumina or chromic oxide. The commercial Alizarin Brown is a mixture of anthragallol with more or less rufigallic acid. 

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