Azo metal complexes

The above-mentioned Pigment Green 10 is the 1 2 nickel complex of the azo pigment obtained from p-chloroaniline and 2,4-dihydroxy-quinoline (33)  

Its synthesis follows the usual pathway of coupling diazotized 4-chloroaniline onto 2,4-dihydroxy-quinoline and subsequently treating the product with a nickel (II) salt. 

The fact that protons are released through complexation makes it sometimes possible to enhance the reaction and to improve the yield by adding a base (such as sodium acetate). 

An interesting product in the range of azo metal complexes is the nickel complex of azo barbituric acid (34) [6]  

This molecule probably assumes the structure of a 1 1 sandwich complex [5], 

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Only a few azo metal complexes are available as pigments. Most of these are very lightfast and weatherfast. The chelating metal is usually nickel, and less commonly, cobalt or iron(II). 

The aromatic moieties are possibly substituted benzene or napthaline rings. In azomethine pigments, only one form of metal complex is possible. This is in contrast to azo metal complexes, which may assume either structure 31 or 32 ... 

The nitrogen atom which is connected to the least nucleophilic aromatic moiety is always the one to serve as a ligand. As is the case with yellow and red monoazo pigments, which have been studied by three dimensional X-ray diffraction analysis (Sec. 2.3.1.1 and 2.5.1), the chelate-6-rings of azo metal complexes prefer the quinonehydrazone structure over the hydroxyazo form [4],... 

Apart from the reaction of o,o -dihydroxyazo compound with a metal salt, there are two more complexation techniques which are worth mentioning, although these are primarily used to synthesize azo metal complex dyes. 

Recent developments in this class prefer azomethine complexes as chemical structures rather than azo metal complexes. The list of commercially available types includes Pigment Green 8 and 10, Pigment Yellow 117,129,150,153,177,179, and Pigment Orange 59,65, and 68, as well as P.R.257. 

The features of chemical constitution associated with the special requirement of solvent solubility include a number of chemical groups on the chromophores. Sulfo groups are often absent, and only hydroxy or amine groups are present. There are mostly cationic and neutral and sometimes also anionic azo, 1 2 azo metal-complex, and a few anthraquinone dyes. An example is C.I. Solvent Yellow 21, 18690 [5601-29-6] (22, 1 2 Chrome alsoC.7. Acid Yellow 121). 

There are two groups of pigment which fall under the general heading of azo metal complexes, the azo metal complexes themselves... 

Other related nickel-containing yellow pigments include antimony nickel titanium oxide and nickel-based azo-metal complexes. 

Changes in the backbone of the sulfonic acid azo dyes often produce drastic changes in properties of the materials. The disulfonic acid (5) is somewhat similar to (3), but is used to color leather red (77). More esoteric dyes have also been developed based on sulfonic acid metal complexes and chitosan-derived materials (78,79). 

An excellent review of metal complex azo dye chemistry has been provided (42). More recent developments ia the field of metal-containing dyes have also been presented (43,44). 

Mordant Dyes. MetaUizable azo dyes are appHed to wool by the method used for acid dyes and then treated with metal salts such as sodium chromate [7775-11-5] sodium dichromate [10588-01-9] and chromium fluoride [1488-42-5] to form the metal complex in situ. This treatment usually produces a bathochromic shift ia shade, decreases the solubUity of the coloring matter, and yields dyeiags with improved fastness properties. The chromium salts can be appHed to the substrate before dyeiag (chrome-mordant or chrome-bottom method), together with the dye ia a single bath procedure (metachrome process), or as a treatment after dyeiag (afterchrome process). 

With azo dyes derived from 4,5-dihydroxy-2,7-naphthalenedisulfonic acid [148-25-4] (chromotropic acid) as the coupling component, metal complex formation occurs with the perihydroxy groups without oxidation. 

The second type is comprised of 2 1 metal complexes of OjO -dihydroxy azo dyes which generally do not contain sulfo or other strongly hydrated groups as found ia the premetallized 2 1 complexes for wool. Thus their solubiUty ia esters, ketones, and alcohols is relatively iacreased. Cl Solvent Violet 1... 

Acid Dyes. These water-soluble anionic dyes ate appHed to nylon, wool, sUk, and modified acryHcs. They ate also used to some extent for paper, leather, food, and cosmetics. The original members of this class aU had one or mote sulfonic or catboxyHc acid groups in thein molecules. This characteristic probably gave the class its name. Chemically, the acid dyes consist of azo (including preformed metal complexes), anthraquiaone, and ttiaryHnethane compounds with a few azHie, xanthene, ketone imine, nitro, nitroso, and quHiophthalone compounds. 

Metallized Azo Dyes. The three metals of importance in azo dyes are copper, chromium, and cobalt. The most important copper dyes are the 1 1 copper(II) azo dye complexes of formula (21) they have a planar stmcture. 

Azo compounds o-am ino-o -hydroxy diary 1 transition metal complexes, 6,57 bidentate dyes, 6,42 o,o -diaminodiaryI cobalt complexes, 6,58,60 o,o -dihydroxydiaryl copper complexes. 6.55,57 pK 6,47... 

Phenol-4-sulfonic acid, 2-(2-hydroxynaphthyl-l-azo)-copper complexes, 6, 55 Phenolysis metal sulfides, 2, 342 Phenylalanine... 

Triphenylformazan behaves as a bidentate ligand forming 2 1 complexes (217) with divalent copper, nickel, and cobalt.377 Formazan metal complexes can be compared to complexes of azo dyes or beta diketones due to structural similarity.301,302 In general, formazan metal complexes have low stability toward acids. However, when electron-donating substituents are added to the aromatic ring, a considerable enhancement in stability is observed. Cationic complexes of type 218 are also known. The complexation of formazan with metal cation can be accompanied by oxidation to the tetrazolium salt and the formation of a complex... 

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