Quinoid dyes

However, benzylidene derivatives show a strong bathochromic shift in comparison with alkylidene derivatives. Thus absorption is a result of the whole conjugated system that is comparable to that of the quinoid dyes. The color of this type of compound is sensitive to acids and bases. 

This reaction is proof of the structure of the dye, easily obtained from the dihydro compound (3). Yields are low as a result of numerous side reactions. The stereochemical configuration of these quinoid dyes is trans. 

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). 

Figure 19. Some quinoid dyes and orf/zo-quinones acting as hydride ion-abstracting mediators, with some values of their turnover frequencies.

Despite the inconveniences, a certain number of studies have been carried out, particularly concerning dyes containing azomethine groups. Such as hydrazones, pyrazolones, formazans, and selenazoles quinoids. Saturated heterocycles, that is, selenazolines and selenazolidines. have also been tackled. Selenium derivatives for pharmacological or physiological applications are little developed by comparison with their thiazole homologs. 

Xanthene dyes (qv) can be either acidic or basic. Acid xanthenes are known to exist in two tautomeric forms. The phenoHc type, or fluorans, are free-acid stmctures such as D C Orange No. 10 (17b) and D C Red No. 21 (17c). Most have poor water solubHity. In contrast to these, the quinoids or xanthenes are usuaHy the highly water-soluble sodium salt counterparts of the fluorans such as D C Orange No. 11 (18) and D C Red No. 22 (21a). Presendy, there are no certifiable basic xanthene colorants. 

Because of tfiek pH sensitivity, antiiocyanins have found littie use as industtial dyes. However, a few having the quinoidal form of anthocyanidin (28) were formedy used as dyes. Two of these were carajurin [491 -93-OJ (29) and dracorhodin [643-56-1] (30) ... 

The merocyanine dye mentioned above shows solvatochromism, which means that the absorption band maximum of the quinoid form (D form) is sensitive to solvent polarity [40,41]. In Fig. 3, the absorption maximum of the solvatochromic band for M-Mc (a low molecular weight merocyanine analog) is plotted against the dielectric constant of 1,4-dioxane/water mixtures [42]. With the relationship... 

Primary amines and substances with reactive methylene groups react with 1,2-naphthoquinone-4-sulfonate to yield intensely colored p-quinoid derivatives, which, in the case of aryl amines, are indophenol dyes [12, 13]. 

Ran J, H-J Knackmuss, A Stolz (2002) Effects of different quinoid redox mediators on the anaerobic reduction of azo dyes by bacteria. Environ Sci Technol 36 1497-1504. 

The chemistry of quinone dyes has been discussed in a series of books entitled The Chemistry of Synthetic Dyes, edited by Venkataraman.1 The general chemistry of quinoid compounds has been discussed by Patai.2 There have been many books that cover quinoid compounds as dyes and pigments but very few discuss the chemistry of the corresponding leuco dyes. Traditional vat dyes are applied to cellulosic fiber in the leuco form. The chemistry of the leuco form of vat dyes is rather simple. Some leuco quinones are quite stable in the solid state and can be stored for a year. Other leuco dyes are unstable in solution and gradually undergo aerial oxidation. 

Anthraquinone leuco dyes are widely known as vat dyes.10 Vat dyes possess extensively conjugated aromatic systems containing two or more carbonyl groups, e.g., anthraquinone, indigoid chromophores. The colored form of vat dyes are insoluble in water. The dyes are applied by a process whereby the dye is converted to the reduced form (leuco dye) which is soluble in water and can penetrate into a cellulosic fiber. On exposure to the atmosphere the leuco form is oxidized to the original quinoid form which then precipitates as an aggregate. Vat dyes generally have excellent chemical and photochemical stability. 

Chen and Laidler [Canadian J. Chem., 37 (599), 1959] have studied the reaction of the quinoid form of bromphenol blue with hydroxide ions to give the carbinol form of the dye. The following values of the second-order rate constant at 25 °C were reported. 

Quinoid-type chromophoric structures, reactions of, 21 36-37 Quinoline (QI), 12 723, 725-726 soluble dyes, 7 373t Quinoline-4-carboxylic acids, 21 190 Quinoline derivatives, 21 196-214 Quinoline-derived drugs, 21 197-198t Quinoline dyes, 21 196 Quinoline, formation of, 21 109. See also Quinolines... 

The desire to increase P values above those of molecules used in the earliest materials has led to the exploration of organic compounds as the active components of second order NLO devices. Considerable effort has been expended in the synthesis and analysis of candidate molecules, which are largely donor-acceptor substituted conjugated n systems. (2) Examples of compound classes whose members display large nonresonant P include azo dyes, stilbenes, polyenes, merocyanines, stilbazolium salts, and quinoid... 

Commercial anthraquinoid vat dyes are dye preparations that consist of a vat-table colored pigment and a dispersing agent. Such vattablepigments are polycyclic quinoid compounds that contain two or more carbonyl groups in a closed system of conjugated double bonds (Section 3.4). 

Articles made of pure PES fibers are dyed almost exclusively in exhaustion processes. Disperse dyes are most stable at a pH of 4-5 (acetic acid). A dispersing agent is also added to the dyebath. Dyes sensitive to heavy metals (e.g., anthra-quinoid red products) are dyed in the presence of a complexing agent (EDTA type). 

A dye is a colored chemical that can impart color to a material or other body on a reasonably permanent basis. Most dyes contain considerable unsaturation, and some part of the dye is usually in the form of aromatic rings with nitrogen unsaturation of several types common to many dyes. The quinoid structure appears frequently, although other dye families are available. 

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