Formazans cobalt complexes

Another class of metal complex dyes is derived from the formazan stmcture. These dyes are appHed to wool and nylon from a neutral or weakly acidic dyebath analogous to the 2 1 premetallized OjO -dihydroxyazo complexes. The bluish-gray dye Cl Acid Black 180 [11103-91-6] (61) (Cl 13710) is a 2 1 cobalt complex of the formazan type. 

Formazan, l-(2-hydroxy-5-suIfophenyl)-3-phenyl-5-(2-carboxyphenyl)-zinc detection, 6, 83 Formazans cobalt complexes dyes, 6, 81 metal complexes bidentate, 6, 78 color photography, 6,111 dyes, 6, 77 tetradentate, 6, 81 tridentate, 6, 79... 

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... 

Wool and Polyamide Dyes. Water-soluble formazan complexes having sulfonamide, alkylsulfonyl, or sulfonic acid groups possess a high affinity to nitrogen-containing fibers. As with acid dyes, they can be used to dye wool and polyamide in neutral to weakly acid baths. Commercial dyes of this type are C.I. Acid Blue 267 and 297, and the 1 2 cobalt complex C.I. Acid Black 180, 13710 [11103-91-6] (29). 

The formazans, which were first discovered in 1892, are derivatives of the hypothetical parent compound (163). Various methods are available for their preparation and a wide range of l,3,S-sub tituted formazans (164) has been synthesized. These are usually brightly and intensely coloured and, following the observation that 1,3,5-triphenylformazan readily formed copper, nickel and cobalt complexes, considerable effort was devoted to developing metal complex formazans as dyestuffs. Very few such compounds have found commercial application, largely because of the ease with which formazans are oxidized to the corresponding tetrazolium salts (165). This property has also led to some confusion regarding the nature of the metal complexes formed by variously-substituted formazans, which is not yet fully clarified. 

Formazan, l-(2-hydroxy-5-sulfophenyl)-3-phenyl-5-(2-carhoxyphenyl)-zinc detection, 83 Formazans cobalt complexes dyes, 81... 

Price, R. Metal complex formazans. I. Reaction of copper and cobalt salts with certain bi- and tridentate... 

The bulk of the literature on the coordination chemistry of formazans deals with complexes of copper, nickel, cobalt, and chromium. 

The preparation of chromium(III) and cobalt(III) complexes of tetradentate formazans in which the coordination sphere of the metal is completed by a variety of neutral ligands has been reported116 and these (185) were claimed to be very stable towards acids. By analogy with copper complexes, however, some doubt must exist regarding the structures assigned to those complexes derived from l,5-bis(2-carboxyphenyl)formazans. Various dyestuff and pigment applications have... 

Metallization. Bident ate formazans that are insoluble in water can be warmed with cobalt, nickel, and copper salts (preferably acetates) to form metal chelates in solvents such as methanol, ethanol, acetone, and dimethylformamide. Metal complexes of tri- and tetradentate formazans are much more stable. Metallization with divalent salts occurs rapidly at room temperature. On reaction with diazo-tized 2-aminophenols or 2-aminonaphthols, coupling and metallization with divalent metal salts can take place concurrently under the same conditions. When coupling is complete, the dye is usually fully metallized. 

Metal-Containing Tridentate Formazans. Formazans substituted with OH or COOH in the 2-position of the N1- or Ns-aryl group have the same complexing properties as 2-hydroxy- (or carboxy)-2-aminodiarylazo dyes. Similarly, they also form 1 1 complexes with four-coordinate metals, and 1 2 complexes with six-coordinate metals. Being N ligands formazans react more readily with cobalt salts than with chromium salts. The mostly blue 1 2 cobalt(m) complexes of type 34 [72] and the mostly gray-blue complexes of type 35 [73] are known. 

Particularly fine colors are displayed by the metal complexes of formazans derived from viscose rayon. The copper, cobalt, and uranium cellulose complexes represent a new type of the so-called chemically colored threads. 

Like the simple formazans, the formazans of oxidized polysaccharides form complexes with heavy metal salts with ease. On warming the formazans of oxidized cellulose, starch, dextrin, dextran, or inulin with copper, cobalt, nickel, or uranium salt solutions, their characteristically-colored metal complexes are obtained. The presence of carboxyl groups in the polysaccharide formazans frequently facilitates complex formation. ... 

Oxidation of formazans with a wide range of oxidizing agents leads to 2,3-disubstituted tetrazolium salts. Recently, oxidations with cupric acetate and cobalt chloride have led to mixtures of metal-formazan complexes and tetrazolium salts arising from competing reactions in which the balance depended on the substituents present in the formazans.462 Reduction of 1,4,5-trisubstituted tetrazolium iodides with NaBH has been used to prepare A2-tetrazolines.463 A similar attempted reduction of 1,3,5-trisubstituted tetrazolium salts gave no reaction.463... 

The oxidation is catalytic in the presence of air and both the chloro and acetate complexes of the metal ion react. In the case of the corresponding cobalt(n) solutions, three products are observed, with evidence for complex formation between the metal ion and formazan with a secondary oxidation step. Surprisingly, however, the activity of the cobalt salts is promoted by the absence of air. E.s.r. evidence has been presented for a short-lived intermediate in the adduct formation between dibutyldithiocarbamatocopper(ii) and N-containing bases of the pyridine and piperidine type. ... 

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