Dyestuffs and Organic Pigments

Essential components of these phosphotungstic lakes are Al, Ba or Ca cations, phosphotungstic (or phosphomolybdic) anions, and a suitable dyestuff, but their precise structural formulation is not known [5]. 

Phosphotungstic lakes have some technical drawbacks, however, and are relatively expensive. Competition from other organic pigments has greatly limited their use. 

In view of the great expansion of heteropoly chemistry in recent years, it seems not unlikely that entirely new lakes may be possible with some of the larger cavity structures (Chapter 5.7). 

Azo dyestuffs, which have the general formula Ar-N=NAr , form the largest and most used class of dyestuffs [6]. They can be formed by reactions of the type (12.47) and (12.48), which are known as diazotisation and coupling, respectively. The availability of an almost endless number of aromatic derivatives Ar and Ar for these reactions (benzene and naphthalene derivatives figuring most prominently) has led to the huge range of azo dyestuffs and pigments known (but not necessarily manufactured) today. 

In the most used direct method of diazotisation (12.47), generally X=C1, but it can be HSO4, H2PO4, and so on. In special cases, for example, weakly basic amines, H3PO4 is sometimes more suitable and is used in place of HCl (the nitrous acid is usually generated by the simultaneous action of more acid, HX, on NaNOj) [7,8], 

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Ecological and Toxicological Association of the Dyestuffs and Organic Pigments Manufacturers, Basel, Switzerland. 

Anliker R, Moser P, Poppinger D. 1988. Bioaccumalation of dyestuffs and organic pigments in fish. Relationships to hydrophobicity and steric factors. Chemosphere 17 1631-1644. 

Guidelines for the S afe Dandling of Dyestuffs in Colour Storerooms, Ecological and Toxicological Association of Dyes and Organic Pigment Manufacturers (ETAD), Basel, Switzerland, June 1983. 

Lumatex [BASF], TM for a series of mineral and organic pigment dyestuffs that can be fixed on all types of textile fibers with suitable binders. 

The development of modern organic pigments started with the synthesis of dyestuffs for the textile industry. The period up to 1900 was characterized by the discovery and development of many dyes derived from coal-tar intermediates. Rapid advances in color chemistry were initiated after the discovery of diazo compounds and azo derivatives (shown to be largely hydrazone derivatives). The wide color potential of this class of pigments and their relative ease of preparation led to the development of azo colors, which represent the largest fraction of manufactured organic pigments. 

Use Ethylbenzene catalyst, dyestuff intermediate, detergent alkylate, ethyl chloride, pharmaceuticals and organics (Friedel-Crafts catalyst), butyl rubber, petroleum refining, hydrocarbon resins, nucleating agent for titanium dioxide pigments. 

Surfactants are used in the so-called flush process in the dye and varnish industry. Organic and inorganic pigments are transferred from an aqueous medium into an oily medium in this procedure. In addition, surfactants disperse pigments in dyestuffs, emulsify pigments in emulsion dyestuffs and stabilize the formulations of dyes and varnishes. 

Dyes and dyestuffs n. Organic coloring substances. Pigment dyestuffs are virtually insoluble in water and in the usual paint and varnish vehicles. Some examples of pigment dyestuffs are toluidine red, phthalo-cyanine blue, and arylamide yellow. Some dyes are soluble in water and organic solvents and are classed according to their solubilities, for example, water-soluble dyes, spirit-soluble dyes, and oil-soluble dyes. Harper CA (2000) Modern plastics encyclopedia. McGraw Hill Professional, New York. 

The focal point of applications in organics lies in aromatic amino acids, proteins such as enzymes, pharmaceuticals in various forms, and natural (native) and synthetic pigments and dyestuffs. 

Both, natural pigments and synthetic organic pigments and dyestuffs have been treated in numerous publications. The fine-resolution of spectra by differentiation makes this technique a particularly powerful tool for identification and for verifying quality and purity (Table 5-16 and 5-26). 

A major disadvantage with this pigment is that while it performs excellently in organic solvent-based coatings, it readily hydrolyzes under aqueous alkaline conditions to form an intense yellow-green fluorescent dyestuff, and is therefore unsuitable for most water-based coatings applications. 

The use of dimethyl sulfoxide (DMSO) as an aid to mutagenic testing of organic HPPs is to be deprecated. This technique is commonly used to render the substance being tested at least partially soluble and thus more bioavailable. In the case of organic pigments, however, any solubilization which may take place essentially transforms the pigment into a bio-available dyestuff, rather than an inert, unreac-tive, and non-bioavailable substance, and can produce false positive test results. 

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