Dyes, use

Hydrazono-5-(p-dialkylaminophenylimino)seienazoles, pyrazolone azomethin selenazoles, quinoid dyes, and formazans are other important dyes used in photography and the color industry (cf. previous sections). 

A dye used in the coloration of materials, such as fibers, must be present as the monomer if it is to adsorb to the material s surface. This experiment describes how spectrophotometry can be used to determine the equilibrium constant between a monomer and a dimer for the dye pinacyanol iodide in water. 

During the drying and, if required, the heat treatment that foUows, the fluorescent whitener is fixed on the substrate. FWAs and dyes used in padding procedures must have low substantivity during the padding operation. This is an important prerequisite for level whitening with no tailing. 

Colored Impregnations. Colored oil to fill cracks is used on gemstones primarily to improve color, most frequendy on emerald. Colored oil is also used to simulate other stones, most frequendy quartz. Depending on the dye used, the colors may fade, in addition to the problems associated with colodess oiling. 

Although lead acetate [301-04-2] is the only metallic dye used ia the early 1990s, salts or silver, copper, nickel, cobalt, bismuth, and iron have been utilized ia the past. A patent (39) refers to the use of bismuth citrate ia a solution made alkaline with triisopropan ol amine. 

The dyes used can be classified in four groups (3) as follows. 

Ketene trimer can be recovered from the tarry residue of diketene distillation and converted into valuable building blocks like 1,3-cyclobutanedione and squaric acid [2892-51-5] (140,141), an important intermediate in the synthesis of pharmaceuticals and squaryHum dyes used in photostatic reproduction (142,143). 

The (A/-alkylated) lactam of 8-aminonaphthalenecarboxylic acid (47) also is a valuable dye iatemiediate, eg, for cyclometbine-type dyes used for dyeiag polyacrylonitrile fibers and other synthetics. 1,8-Naphtholactams are prepared in high yield and purity by the reaction of naphtholactones with RNH2 (R = H, Cl—4 alkyl, cycloalkyl, or optionally substituted aryl) in aqueous medium, usually in the presence of bisulfite at 150°C over a period of 15 h (143). 

Table 5. Typical Basic Dyes Used as Complexes with Heteropolyacids...

The requited characteristics of dyes used as passive mode-locking agents and as active laser media differ in essential ways. For passive mode-locking dyes, short excited-state relaxation times ate needed dyes of this kind ate characterized by low fluorescence quantum efficiencies caused by the highly probable nonradiant processes. On the other hand, the polymethines to be appHed as active laser media ate supposed to have much higher quantum efficiencies, approximating a value of one (91). 

The color and effect produced by NGR stains and any stain mixture depend on several factors other than the colors or type of dyes used. Those factors include strength of the mixture, the amount appHed, the type of substrate, and the solvent system used for the stain. The role of the wood stain is not to provide protection rather, the primary function of the stain is to impart color effects by accentuating grain patterns. The transparency and brightness needed to enhance the natural beauty of the wood are optimized by using dye-type stains for wood. 

Direct Orange 15 (Cl 40003) [1325-35-5] (13), which is made by reducing the alkaline condensation product equivalent to Direct YeUow 11 with sulfide or formaldehyde, is an important paper dye used in dyeing brown paper for bags. 

Wool is dyed from aqueous solutions. The majority of dyes used on wool are sodium salts of aromatic anions. Water solubiUty is usually provided by sulfonic acid groups, but in a few cases carboxyl or hydrophilic, nonionic substituents are used. 

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. 

Around 1800, the attack of chromite [53293-42-8] ore by lime and alkaU carbonate oxidation was developed as an economic process for the production of chromate compounds, which were primarily used for the manufacture of pigments (qv). Other commercially developed uses were the development of mordant dyeing using chromates in 1820, chrome tanning in 1828 (2), and chromium plating in 1926 (3) (see Dyes and dye intermediates Electroplating Leather). In 1824, the first chromyl compounds were synthesized followed by the discovery of chromous compounds 20 years later. Organochromium compounds were produced in 1919, and chromium carbonyl was made in 1927 (1,2). 

Miscellaneous Uses. Inks used by inspectors to stamp the grade or quaUty on meat must, bylaw, be made from food-grade colors. Dyes used in packaging materials that come in direct contact with a food must also be food-grade or, if not, it must be estabUshed that no part of the colorant used migrates into the food product. Pet foods, too, if colored, must contain only those colorants recognized by the FDA as suitable for the purpose. 

Fig. 3. Miscellaneous dyes used in cosmetics and medical devices. Dye classification (32), azo (33), anthraquinone (34), phthalocyanine (35), indigoid.

The colorant is prepared by leaching the annatto seeds with an extractant prepared from one or more approved, food-grade materials taken from a hst that includes various solvents, edible vegetable oils and fats, and alkaline aqueous and alcohoHc solutions (46,47). Depending on the use intended, the alkaline extracts are often treated with food-grade acids to precipitate the annatto pigments, which ia turn may or may not be further purified by recrystallization from an approved solvent. Annatto extract is one of the oldest known dyes, used siace antiquity for the coloring of food, textiles, and cosmetics. It has been used ia the United States and Europe for over 100 years as a color additive for butter and cheese (48—50). 

A. I. Solodukhin, Proipv. Isol i Uitaminov, Antihiotikov Biol Aktivn. Ueshchestv, 145—181 (1965). Production and Use of Food Dyes. A review of the synthetic and natural food dyes used in the Soviet Union. 

Dye Stability. The dyes used in photographic systems can degrade over time, both by thermal reactions and, if the image is displayed for extended periods of time, by photochemical processes. The relative importance of these two mechanistic classes, known as dark fade and light fade. 

Nitro and Nitroso Dyes. These dyes are now of only minor commercial importance, but are of interest for their smaU molecular stmctures. The early nitro dyes were acid dyes used for dyeing the natural animal fibers such as wool and sUk. They were nitro derivatives of phenols, eg, picric acid [88-89-1] (73) (Cl 10305), or naphthols, eg. Cl Acid YeUow 1 [846-70-8] (74) (Cl 10316). 

Fig. 1. Anthraquinone dyes used as organic pigments (4) = dibromoan than throne [4378-61-4] (Cl Pigment Red 168 Cl Vat Orange 3 Cl 5930G) (5) = an anthrapyrimidine [4216-01 -7] (Cl Pigment YeUow 108 Cl Vat YeUow 20 Cl 68420)-, (6) = indanthrone blue [81-77-6] (Cl Pigment Blue 60 Cl Vat Blue 4 ...

The dyes used in the ink sheet must satisfy various requirements (/) optimum color characteristics of the three primary colors (hue, color density, shape of absorption spectmm) (2) sensitivity, ie, sublimabiHty from ink sheet to acceptor sheet (3) fastness for light and migration and (4) compatibiHty with the resin in the ink sheet. With respect to these characteristics, a large number of anthraquinone dyes have been proposed particularly for magenta and cyan colors. Typical examples are given in Table 8 and Table 9. 

The majority of vat dyes used worldwide are appHed by continuous dyeing polyester—cotton blends are the most important substrate. The fabric is padded with vat dye dispersion, dried, padded with sodium hydrosulfite, caustic soda, and salt, steamed for 30—60 s at 102°C, rinsed, and dried. 

Because it is also a proteia, silk can be dyed as wool, but ia practice the dyes used are generally acid dyes ia view of the fiber not being treated to any severe washing ia its life. The main difference between wool and silk is ia the preparation of the fiber for dyeiag. 

In method (2) the fiber-reactive dye is appHed with alkaH. The choice of alkaH and batching times and temperature are dependent on the fiber-reactive dye used. 

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