Azo compounds metal complexes

METAL COMPLEXES OF AZO DYES Metal complexes of certain 0,0 -dihydroxyazo, 0-carboxy-0 -hydroxyazo, o -amino-o hydroxyazo, arylazosalicyclic acid, and formazan compounds are used as dyes for wool, nylon, and cotton with generally much improved washfastness and lightfastness properties when compared to their respective unmetallized precursors. Dyes that are chelated with the metal on the substrate during the dyeing process are termed metallizable or mordant dyes. Conversely, those dyes that have been metallized by the dye manufacturer prior to use by the dyer, are classified as premetallized dyes. The two important types of premetallized dyes are the 1 1 and 2 1 complexes, eg, complexes with 1 1 and 2 1 ligand-to-metal ratios, respectively. 

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. 

Thermolysis rates are enhanced substantially by the presence of certain Lewis acids (e.g. boron and aluminum halides), and transition metal salts (e.g. Cu ", Ag1).46 There is also evidence that complexes formed between azo-compounds and Lewis acids (e.g. ethyl aluminum scsquichloridc) undergo thermolysis or photolysis to give complexed radicals which have different specificity to uncomplexed radicals.81 83... 

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... 

The application range designated by this generic name in the Colour Index incorporates those acid, direct and mordant dyes with substantivity for leather and satisfactory fastness on that substrate [55]. It is a commercially important sector, the number of products listed being exceeded only by the complete acid or direct dye ranges. As expected from the sources of this selection, about 85% of leather dyes are azo compounds (35% disazo, 30% monoazo, 20% metal-complex monoazo) and the remainder are mainly yellow to orange stilbene dyes and anthraquinone or triarylmethane types in the violet to green sectors. 

The commercially most interesting metal complex pigments within the azo series are those obtained from aromatic o,o -dihydroxyazo compounds, while important products within the azomethine series are nickel or copper complexes of aromatic o,o -dihydroxyazomethine compounds. 

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. 

Commercially available azo and azomethine metal complex pigments cover the spectral range from considerably greenish to reddish yellow and yellowish orange. Compared to their parent structures (the corresponding azo and azomethine compounds), azomethine metal complexes frequently exhibit a distinctly duller shade. Formation of the metal complex often shifts the color of an originally yellow material in the greenish yellow direction. 

On the other hand, we believe that greater attention should be focused to the fact that metal ions will form chelated complexes with azo compounds. Hence a vigorous post treatment with acids should be attempted if the stability of the product permits. Usually this treatment should be carried out before a final crystallization. 

Some coordination compounds have been used as dyes and pigments, but it must be admitted that these applications developed without reference to the fact that the compounds are complexes. Examples of paint pigments are Prussian blue and the phthalocyanines metallized azo dyes are common in the textile industry. 

The next milestone in the history of chromium dyes for wool arose from the observation that 1 1 chromium complex dyestuffs react with a second molecule of a metal-free, tridentate azo compound to give the 2 1 chromium complex. If the second dyestuff is the same as that from which... 

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