Pigments synthesis methods

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

Anthraquinone An aromatic compound comprising two benzene rings linked by two carbonyl (C=0) groups, CgH4(CO)2CgH4. Combustible. Used as an intermediate in organic synthesis, mainly in the manufacture of anthraquinone dyes and pigments. One method of preparation is by condensation of 1,4-naphthaquinone with butadiene. 

Pure metal nanoparticles have shown exceptional catalytic properties which have motivated modem researchers to come up with innovative ideas to synthesize nanoparticles in a cost effective manner. Apart from catalysis, potential applications of metal nanoparticles ate well known in other fields such as pigments, electronic and magnetic materials, dmg deUvery etc. Here we report solution combustion synthesis method to synthesize transition metals (Ni, Cu and Co) in a single step process. Metal nitrates and glycine are used as synthesis precursors and dissolved in water to make a homogeneous aqueous solution which is combusted to produce metal nanoparticles with desired composition. 

The synthesis of carbonyl colorants uses a wide diversity of chemical methods, in which each individual product essentially has its own characteristic route. This is in complete contrast to the synthesis of azo dyes and pigments (Chapter 3) where a common reaction sequence is universally used. The subject is too vast to attempt to be comprehensive in a text of this type. The following section, therefore, presents an overview of some of the fundamental synthetic strategies which may be used to prepare some of the more important types of carbonyl colorants. 

The solution to this difficulty, discovered by Schmid of Ciba in the early 1950s, is to reverse the order of the two steps. The diazotised amine is first coupled with BON acid and then two moles of this intermediate are condensed with one mole of benzidine in the form of its hydrochloride. The condensation is carried out in a high-boiling solvent such as nitrobenzene, when yields of 95% can be attained. These pigments have been called azo condensation pigments in view of their method of synthesis. 

Quite apart from the problems of chemical synthesis, it is clear that the application of physico-chemical methods to pigment manufacture, first needed in the development of the... 

The most extensive compilation of information about pigments is in the volume Pigments and Solvent Dyes (1997), which is part of the Colour Index. For various reasons, there is now less technical information about the chemistry of the synthesis and manufacturing methods for pigments than appeared in the 1982 volume, although much of this was in references to patents. 

The synthesis of the crystal modification is controlled primarily by the finishing technique of the crude pigment. There are basically two different methods to produce a finely dispersed pigment treatment with acid to form copper phthalocyanine salts, followed by precipitation in water on the one hand, and mechanical treatment (milling, kneading) on the other hand. The following methods are used ... 

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. 

Route B of this process may be substantially improved in terms of yield and product quality (purity) of the resulting triarylaminoarylcarbonium pigment. To this end, the solution of the free dye base is treated with an excess of aqueous sulfuric acid (20 to 40% ) in a solvent such as chlorobenzene or an aromatic amine. This method produces the sulfate of the basic dye, which is insoluble in this medium, together with the soluble sulfates of the primary aromatic amines, which can therefore easily be separated. The isolated sulfate of the basic dye is then washed and in dry or wet condition monosulfonated with 85 to 100% sulfuric acid. Based on the dye base sulfate, this step affords 96 to 98% yield, compared to only 83 to 89% achieved by the previously described method. The entire synthesis, including the intermediate isolation of the triarylaminoarylmethane sulfate, may also be performed by continuous process [3]. 

For the synthesis of the natural blue pigment trichotomine dimethyl ester, L-Trp-OMe was used as a starting material. The first step of this synthesis was conversion into methyl l-methyl-3,4-dihydro-/8-carboline-3-carboxylate with acetyl chloride in TFA (85JOC3322). An improved method starts from the corresponding thioamides via thioiminium salts which cyclize spontaneously in refluxing solvent (82CPB4226). A-Formyl-tryptophan also cyclized readily with no side reactions (68CJC3404). 

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