Other Dyes

Aniline when freshly distilled is a colourless liquid of b.p. 184° and d, 1025 on exposure to air and light, it develops a deep brown colour. It is an extremely important substance technically, being the starting point of many azo and other dyes. 

The use of sensitizing dyes in photography has been the subject of many studies and constitutes. still now. one of the most studied areas in specialized periodic publications (125, 126) or in textbooks (88. 127). It can be ascertained that one hundred years after Vogel s discovery of spectral sensitization, the basic mechanisms of action of dyes on their silver halide support still remain not fully understood. However, the theoretical reasons explaining why among many other dye families practically only cyanine methine dyes appear to be spectral sensitizers (128) are better known. 

Solvent Influence. Solvent nature has been found to influence absorption spectra, but fluorescence is substantiaHy less sensitive (9,58). Sensitivity to solvent media is one of the main characteristics of unsymmetrical dyes, especiaHy the merocyanines (59). Some dyes manifest positive solvatochromic effects (60) the band maximum is bathochromicaHy shifted as solvent polarity increases. Other dyes, eg, highly unsymmetrical ones, exhibit negative solvatochromicity, and the absorption band is blue-shifted on passing from nonpolar to highly polar solvent (59). In addition, solvents can lead to changes in intensity and shape of spectral bands (58). 

The range of colors covers all hue classification groups except a tme red. As a rule, the hues are dull compared with other dye classes. Black is the most important, followed by blues, oHves, and browns (see Dyes and dye intermediates). 

Short-chain alkylated biphenyls are the principal biphenyl derivatives in commercial use. They are generally produced by Hquid-phase Friedel-Crafts alkylation of biphenyl with ethylene, propylene, or mixed butenes. A series of mixed ethylated biphenyl heat-transfer fluids (trademarked Therm S-600, 700, 800) is marketed by Nippon Steel. A mixed diethylbenzene—ethylbiphenyl heat-transfer fluid is also available from Dow (63). Monoisopropylbiphenyl [25640-78-2] largely as a mixture of meta- and para-isomers is produced by Koch Chemical Co. Monoisopropylbiphenyl (MIPB) was selected by Westinghouse (64,65) as a PCB replacement in capacitors and this is its primary appHcation today. For a time MIPB was also employed as a PCB replacement in pressure sensitive copy paper, but this outlet has since given way to other dye solvents. A similar product consisting of a mixture of j -butylbiphenyl isomers [38784-93-9] (66) is currently the favored dye solvent for pressure sensitive copy paper (67) manufactured in the United States. 

A recent addition to Table 3, Reactive Blue 246 differs from the other dyes and is not added to a finished lens. The dye molecule has methacrylate groups attached to an anthraquinone and is incorporated directiy into the polymer matrix during polymer cure (175). This in-monomer concept has the potential to reduce dramatically the cost of visibiUty tinting of a contact lens. 

Powerful solvents such as dimethyl sulfoxide (common laser dye solvent) and solubilizing substituents (K" and R " = sulfoalkyl in stmcture 32) may enhance the transport of dyes in solution through skin and other membranes. Reference 88 (on laser dye solutions and toxicity) is recommended to researchers working with dye solutions. Other dyes, such as Indocyanine Green, attain useful properties (blood tracer dye) as a result of having solubilizing substituents in their stmcture. 

Properties. The principal advantages of anthraquiaone dyes are brightness and good fastness properties, but they are both expensive and tinctorially weak. However, they are stiU used extensively, particularly ia the red and blue shade areas, because other dyes caimot provide the combination of properties offered by anthraquiaone dyes, albeit at a price. 

Sulfur Dyes. These dyes are synthesized by heating aromatic amines, phenols, or nitro compounds with sulfur or, more usually, alkah polysulfides. Unlike most other dye types, it is not easy to define a chromogen for the sulfur dyes (qv). It is likely that they consist of macromolecular stmctures of the phenothiazone-thianthrone type (72), in which the sulfur is present as (sulfide) bridging links and thiazine groups (1). 

The principle of each process is briefly described ia the Hterature (170). Some anthraquiaoae dyes and pigments appear to be used ia combination with other dye or pigment classes such as phthalocyaniaes and carbazole violets, etc. Two examples described ia pateats are the red pigment and blue dye that foUow ... 

Other dyes in this group are phthalocyanine compounds which stiU have commercial importance, particularly in textile printing. 

Because of the limitations of direct dyes and the abiHty to use simple acid dye chromophores to give bright washfast dyeings, fiber-reactive dyes have become a weU-estabHshed, popular way of dyeing cellulose. A market of 56,000 t of reactive dyes was forecast for cellulose fibers in 1989 (18), and the growth rate of reactive dye consumption of 3.9% per annum is four times the growth rate of other dyes for ceUulosic fibers (19). 

Nylon is similar ia its general chemical stmcture to the natural fiber wool, and therefore all the previously described processes for wool are appHcable to dyeiag nylon with acid, metallised, and other dyes. There are, however, significant differences. Nylon is synthetic, it has defined chemical stmcture depending on the manufactufing process, and it is hydrophobic (see Fibers, POLYAMIDES). 

Acetate fibers are dyed usually with disperse dyes specially synthesized for these fibers. They tend to have lower molecular size (low and medium energy dyes) and contain polar groups presumably to enhance the forces of attraction by hydrogen bonding with the numerous potential sites in the cellulose acetate polymer (see Fibers cellulose esters). Other dyes can be appHed to acetates such as acid dyes with selected solvents, and azoic or ingrain dyes can be apphed especially for black colorants. However thek use is very limited. 

Azoic Dyes. These are used to produce cost-effective heavy yellow, orange, red, maroon, navy blue, brown, and black shades and are ptinted alongside other dye classes to extend the coloristic possibiUties for the designer. Two approaches are adopted. The common method ia the United States is to use both a naphthol derivative and a stabilized color base, usually in the form of a diazo imino compound in the same print paste. This mixture is soluble in dilute caustic soda and no coupling takes place at this stage. The dried prints are passed through steam at 100—105°C that contains acetic and/or formic acid vapor. As neutralization takes place on the print, the coupling occurs rapidly and the insoluble azoic dye is formed. 

Theoretically, the dye or chromogen can be any colored species. Of course, requirements for fastness, solubiUty, tinctorial value, ecology, and economy must be met. Most commonly used chromophores parallel those of other dye classes. Azo dyes (qv) represent the largest number with anthraquiaone and phthalocyanine making up most of the difference. Metallized azo and formazan dyes are important and have gained ia importance as a chromophore for blue dyes duriag receat years (6) (see Dyes and dye intermediates). 

FD C Red 40 is used as a coloring agent in a wide array of products, such as orange soda. It is related to several other dyes, including FD C Yellow 6 ... 

A typical procedure is shown in Figure 2. Other dyes besides ethidium can be used, although ethidium has an advantage in that its excitation emission bands are well removed from any protein absorbances. A standard curve can be constructed for the nucleic acid of concern and the limits of detection established. In Step 3, proteolytic enzymes may be substituted for heparin, or the step may be bypassed in the case of proteins which do not interfere. After measurement of the unknown sample the nucleic acid concentration may be simply calculated or read from the standard curve. 

In order to further extend the utility of fluorescence methods the use of time-resolution methods, fluorescence polarization, and laser techniques should be explored. The addition of other dyes with enhanced fluorescence properties on binding and increased selectivity to various types of nucleic acids will be necessary to further develop more useful analytical methods. 

The two-electron oxidation of the dye is not very common other dyes usually undergo one-electron redox reactions. The cathodic reaction (taking place in the non-illuminated cell compartment) regenerates the complementary redox system ... 

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