Dyes, theory

These results have led to the conclusion that ionic mechanisms alone do not entirely explain the complex interactions that occur between basic dyes and acrylic fibres. Hydrophobic interaction also plays an important part and it has been demonstrated [55] that multivalent anions such as sulphate or phosphate can enhance the hydrophobic interaction, thereby also increasing dye sorption in some circumstances. Whilst such results are of interest in terms of dyeing theory, it is extremely doubtful whether there will ever be practical interest in exploiting the use of electrolytes at such high concentrations. 

Donnan wool dyeing theory, 26 394 Donohue correlation, 13 262-263... 

Dyeing applications, tetrahydrofurfuryl alcohol in, 12 279 Dyeing theory, 26 394-395 Dyeing transition temperature, 9 159 Dye intermediates, 9 265-298 chemistry, 9 266-291 classification, 9 265-266 economic aspects, 9 293-295 equipment and manufacture, 9 291-293 health and safety factors, 9 295-298 obtained by nitration, 9 2 7 It obtained by sulfonation, 23 525 unit processes, 9 269-283 Dye lasers, 74 702-705 23 144 output characteristics of, 74 705 Dye-ligand affinity chromatography, 6 402 Dye liquor, 9 163 Dye manufacturing... 

The behavior of insoluble monolayers at the hydrocarbon-water interface has been studied to some extent. In general, a values for straight-chain acids and alcohols are greater at a given film pressure than if spread at the water-air interface. This is perhaps to be expected since the nonpolar phase should tend to reduce the cohesion between the hydrocarbon tails. See Ref. 91 for early reviews. Takenaka [92] has reported polarized resonance Raman spectra for an azo dye monolayer at the CCl4-water interface some conclusions as to orientation were possible. A mean-held theory based on Lennard-Jones potentials has been used to model an amphiphile at an oil-water interface one conclusion was that the depth of the interfacial region can be relatively large [93]. 

It appears now that, whatever its usefulness, the resonance theory is somewhat inadequate in explaining and predicting either chemical or physical characteristics of dyes compared to more or less sophisticated molecular orbital calculations. 

Most of the qualitative relationships between color and structure of methine dyes based on the resonance theory were established independently during the 1940 s by Brooker and coworkers (16, 72-74) and by Kiprianov (75-78), and specific application to thiazolo dyes appeared later with the studies of Knott (79) and Rout (80-84). In this approach, the absorptions of dyes belonging to amidinium ionic system are conveyed by a group of contributing structures resulting from the different ways of localization of the 2n rr electrons on the 2n l atoms of the chromophoric cationic chain, rather than by a single formula ... 

Likewise, quantum mechanical calculation succeeds in giving a theoretical explanation of some facts that the resonance theory could not explain, for example, why bis(pyridine-2)monomethine cyanine and bis(pyridine-4)monomethine cyanine possess the same lowest energy transition contrary to the 2,2 - and 2,4 -quinoline monomethine dyes, together with a molecular coefficient extinction lower than that of the 4,4 -quinoline dye (11). Calculation shows also that there is no theoretical reason for observing a relationship between and pK in a large series of dyes with different nuclei as it has been postulated, even if limited observations and calculations in short homogeneous series could lead to this conclusion (105). 

A great number of monoaza or polyaza. either symmetrica] or unsym-metrical, mono trimethine thiazolocyainines have been synthesized in order to verify or to obtain semiempirical rules, more or less based on the resonance theory, concerning the relation between the color of a thiazolo dye and the number and place of nitrogen atoms in the chromophoric chain. For example. Forster s rule applies to ionic dyes and stipulates that the will increase with the decreasing tendency of chromophoric atoms lying between the two auxochromes to take up the characteristic charges (90). 

Although better known now for his incorrect theory that cycloalkanes were planar Baeyer was responsible for notable advances in the chemistry of organic dyes such as indigo and was awarded the 1905 Nobel Prize in chemistry for his work in that area... 

The utility of acid-base titrimetry improved when NaOH was first introduced as a strong base titrant in 1846. In addition, progress in synthesizing organic dyes led to the development of many new indicators. Phenolphthalein was first synthesized by Bayer in 1871 and used as a visual indicator for acid-base titrations in 1877. Other indicators, such as methyl orange, soon followed. Despite the increasing availability of indicators, the absence of a theory of acid-base reactivity made selecting a proper indicator difficult. 

Copolymer composition can be predicted for copolymerizations with two or more components, such as those employing acrylonitrile plus a neutral monomer and an ionic dye receptor. These equations are derived by assuming that the component reactions involve only the terminal monomer unit of the chain radical. The theory of multicomponent polymerization kinetics has been treated (35,36). 

If the perturbations thus caused are relatively slight, the accepted perturbation theory can be used to interpret observed spectral changes (3,10,39). The spectral effect is calculated as the difference of the long-wavelength band positions for the perturbed and the initial dyes. In a general form, the band maximum shift, AX, can be derived from equation 4 analogous to the weU-known Hammett equation. Here p is a characteristic of an unperturbed molecule, eg, the electron density or bond order change on excitation or the difference between the frontier level and the level of the substitution. The other parameter. O, is an estimate of the perturbation. 

Color Mixing. The various types of dye powders used to make dye stains are blended to achieve the desired color. Most finishers purchase wood stains premixed to specified colors. In the wood-finishing industry, various shades of brown are the most common. These colors are usually blended from primary colors. Color-matching skills can be acquired only by practice, but the basic theory of color matching is relatively simple and easily understood. The basic theory of color matching can be demonstrated by using the color circle shown in Figure 1 (see Color). 

The color and constitution of cyanine dyes may be understood through detailed consideration of their component parts, ie, chromophoric systems, terminal groups, and solvent sensitivity of the dyes. Resonance theories have been developed to accommodate significant trends very successfully. For an experienced dye chemist, these are useful in the design of dyes with a specified color, band shape, or solvent sensitivity. More recendy, quantitative values for reversible oxidation—reduction potentials have allowed more complete correlation of these dye properties with organic substituent constants. 

Ta.utomerism. In theory, a2o dyes can undergo tautomerism a2o/hydra2one for hydroxya2o dyes a2o/imino for aminoa2o dyes, and a2onium /ammonium for protonated a2o dyes. A more detailed account of a2o dye tautomerism can be found elsewhere (7). 

Quinophthalones. Like the hydroxy azo dyes, quiaophthalone dyes can, ia theory, exhibit tautomerism. Because the dyes are synthesized by the condensation of quiaaldine derivatives (69) with phthaUc anhydride, they are often depicted as stmcture (70), but this is iacorrect, siace the two single bonds prevent any conjugation between the two halves of the molecule. 

Basic Theory of Fiber-Reactive Dye Application. The previously described mechanisms of dyeing for direct dyes apply to the apphcation of reactive dyes in neutral dyebaths. In alkaline solutions important differences are found. The detailed theoretical treatments are described elsewhere (6) but it is important to consider some of the parameters and understand how they influence the apphcation of fiber-reactive dyes. 

Atomic velocity distribution, 130,131 Atomic volume, 94, 98 alkali metals, 94 halogens, 97 inert gases, 91 third-row elements, 101 Atomic weight, 33 table, inside back cover Atoms, 21 conservation of, 40 electrical nature of, 236 measuring dimensions of, 245 Avogadro, Amadeo hypothesis, 25, 52 hypothesis and kinetic theory, 58 law, 25 number, 33 Azo dyes, 344... 

It has become recognized during recent years that the color of dyes is associated with the resonance of electric charge from atom to atom of the dye molecule.2,3> 4 6 6 Because of the complexity of the problem, however, it has not been easy to expand this idea into a theory of color permitting the rough quantitative calculation of the frequencies and intensities of the absorption bands of dyes. I have now developed a theory of this nature the theory and some of the results of its application are described briefly in the following paragraphs. 

---