Pigments industrial synthesis

The pigment industry today provides the user with a wide variety of pigment preparations to suit all purposes. In these pigment preparations, the pigment is in an already dispersed form. Purchasing a pigment in such a form considerably facilitates its application. Details regarding the composition, synthesis, and application of such preparations are described under the respective applications (Sec. 1.8.1, 1.8.2,1.8.3). 

Several synthetic pathways for the commercial manufacture of quinacridone pigments have been published. In this context, only those routes are mentioned which were developed for industrial scale production. There are four options, the first two of which are preferred by the pigment industry. It is surprising to note that these are the methods which involve total synthesis of the central aromatic ring. On the other hand, routes which start from ready-made aromatic systems and thus might be expected to he more important actually enjoy only limited recognition. 

Synthesis of Copper Phthalocyanine Starting from Metallic Copper (Without Electrolysis) [41] (This Method is Widely Used in the Pigment Industry)... 

The enormous amount of work on phthalocyanins1 reflects their prime importance to the dye and pigment industry and is attested to by the numerous patents in the literature. It is our experience, however, that these materials are rarely pure and that their purification, from unknown impurities, is invariably more troublesome than performing the complete synthesis. Phthalocyanins are stronger o-donors than porphines, and the former stabilize higher oxidation states of coordinated metals,2 while the tetrabenzoporphyrins have properties more characteristic of porphines. 

The preferred starting material for the industrial synthesis of isoindoline pigments is diiminoisoindohne (10a) or its tautomeric form aminoiminoisoindoline (10b), which can be produced from o-phthalodinitrile (9) and gaseous ammonia in ethylene glycol or other suitable solvents. Suitable starting materials further include l,l-dialkoxy-3-iminoisomdolines, synthesized from 9 and C1-C4 alcohols . ... 

Orga.nic Colora.nts. The importance of coal-tar colorants cannot be overemphasized. The cosmetic industry, in cooperation with the FDA, has spent a great deal of time and money in efforts to estabUsh the safety of these dyes (see Colorants for food, drugs, cosmetics, and medical devices). Contamination, especially by heavy metals, and other impurities arising from the synthesis of permitted dyes are stricdy controlled. Despite this effort, the number of usable organic dyes and of pigments derived from them has been drastically curtailed by regulatory action. 

This section provides an overview of the synthesis of dyes and pigments used in textiles and related industries. Dyes are soluble at some stage of the application process, whereas pigments, in general, retain essentially their particulate or crystalline form during application. A dye is used to impart color to materials of... 

Cochineal pigments are extracted from dried bodies of female insects with water or with ethanol the result is a red solution that is concentrated in order to obtain the 2 to 5% carminic acid concentration customary for commercial cochineal. For carmine lakes, the minimum content of carminic acid is 50%. An industrial procedure applied in Spain uses ammonium hydroxide as the extracting agent and phosphoric acid as the acidifying agent. For analytical purposes the extraction is carried out with 2 N HCl at 100°C. The chemical synthesis of carminic acid has also been reported and is the subject of European and United States patents. ... 

Used industrially for electroplating, precious metal extraction and in the synthesis of dyes, pigments, pharmaceuticals, and pesticides. 

The chemical synthesis of linear turns-quinacridones and their substituted derivatives that have been marketed subsequently is a complicated multi-stage sequence, making such pigments very expensive and sustainable only where high-fastness red pigments are essential, as in the car industry. There are four routes of synthesis, details of which have been given by Pollack [27]. 

Depending on the technical requirements such as corrosion resistance, pressure and temperature stability, industrial scale azo pigment synthesis is carried out in appropriate equipment. Suitable materials include cast iron, stainless steel, steel lined with rubber, acid-proof brick, enamel, synthetic resins supported by glass fiber, and wood. 

As a class, these compounds are related to indigo, which is the oldest of all vat dyes. Indigo itself, during its comparatively short history as a commercial pigment, was used especially in rubber. Its structure was first described in 1883 by A.V. Bayer. Knowledge of this structure, together with the development of an industrial scale synthesis, facilitated the development of a series of indigo-based colorants. 

The chemicals trade has gained in significance like trade as a whole. Chemicals exports have tripled since 1980 (in absolnte tnmover figures), while imports have quadmpled l Many synthesis processes, which twenty years ago were still a domain of German and European industry (e.g. organic pigments), can today be performed in India or in Asia. 

The synthesis route chosen for a particular product is governed by all the above considerations. There are three major synthesis methods for industrial pigments ... 

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. 

Segmented gas-liquid (Taylor) flow was used for particle synthesis within the liquid slugs. Tetraethylorthosilicate in ethanol was hydrolyzed by a solution of ammonia, water and ethanol (Stober synthesis) [329]. The resulting silicic acid monomer Si (OH)4 is then converted by polycondensation to colloidal monodisperse silica nanoparticles. These particles have industrial application, for example, in pigments, catalysts, sensors, health care, antireflective coatings and chromatography. 

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