Copper complexes formazans

There are bi-, tri-, and tetradentate formazan dyes7 but only the tetradentate copper complex formazan dyes have found use as commercial products. The dye Cl Reactive Blue 160, of generic structure (41), is a representative example. Because of the intensity of their colors, the metal complex formazan dyes have also found application in analysis. Thus, the dye (42) detects zinc at a concentration of 1 part in 50 million.31... 

The relative importance of these reactions is governed by the stability of the copper complex formazans towards acids. In the case of the bidentate formazans, the equilibrium (16) lies well to the left and such formazans are stoichiometrically oxidized to tetrazolium salts by copper(II) acetate. Tridentate formazans react with copper(II) acetate to give copper(II) complexes but are stoichiometrically oxidized to tetrazolium salts by copper(II) chloride. With the exception of... 

Formazan, l-(2-hydroxyphenyl)-3-phenyl-5-(2-carboxyphenyl)-copper complexes dyes, 6, 81... 

The IR bands in a number of nickel complexes of triaryl formazans have been assigned by Arnold and Schiele.415 A similar assignment of the electronic bands has been carried out.414 LCAO-MO calculations correlate well with these assignments417 and have been extended to include both inner ligand transitions as well as charge transfer bands and d—d transitions.418 EPR spectra have been used to study the nature of bonding in copper complexes of heterocyclic-containing formazans.419 Metal formazan complexes have also been studied by electrochemistry.283,398 420-422... 

An appropriate ion-specific electrode was found to provide a convenient, precise and relatively inexpensive method for potentiometry of copper(II) ion in copper-complex azo or formazan dyes. Copper(II) ion in copper phthalocyanine dyes can be quantified after anion exchange. Twelve commercial premetallised dyes evaluated using this technique contained copper(II) ion concentrations in the range 0.007 to 0.2%. Thus many copper-complex direct or reactive dyes are likely to contribute low but possibly significant amounts of ionic copper to textile dyeing effluents [52]. 

Formazan dyes bear a formal resemblance to azo dyes, since they contain an azo group. The most important formazan dyes are the metal complexes, particularly copper complexes, of letradentate formazans. They are used as reactive dyes far cotton. 

More recent work117 has brought to light other, surprising, differences between l-(2-carboxy-phenyl- and l-(2-hydroxyphenyl)-formazans and cast some light on the structures of their copper complexes. Like 1,3,5-triphenylformazan, both l-(2-carboxyphenyl)- and l-(2-hydroxyphenyl)-... 

Comparison117129 of the behaviour of bidentate, tridentate and tetradentate formazans with copper(II) salts has effectively demonstrated that two competing reactions occur copper complex formation (equation 16) and oxidation of the formazan to tetrazolium salt (equation 17). 

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... 

The coordinatively unsaturated complexes are even less soluble in organic solvents such as diethyl ether, benzene, and chloroform than their saturated equivalents. The magnetic moment of copper complexes of tridentate formazans with a 2-hydroxyaryl substituent at N1 is very low (1.44 iB) compared to the expected value of copper(n) complexes with an unpaired electron and strong covalent bonding. The low solubility and magnetic moment suggest that the dimerization occurs with the formation of a saturated dinuclear complex 38. 

Complexes of formazans having one or two carboxylic groups in the 2- or 2,2-positions of the aryl substituents, however, appear to be bicyclic. Thus, a hydrate was obtained on reaction of l,5-bis(2-carboxyphenyl)-3-cyanoformazan with copper acetate [76], The coordinated water could not be removed by drying and produced a broad band in the IR spectrum at 3450 cm-1. The copper complexes of formazans containing carboxyl groups were then assigned the structure 42. 

Copper complexes of the formazan dye series (see Sections 2.10 and 3.11) are another alternative to reactive anthraquinone dyes they produce red to greenish-blue shades. Like triphenodioxazine dyes, copper formazans exhibit high molar extinctions ( e = 25 000 -30 000). These materials are derived from l-(2-hydroxyphe-nyl)-3-phenyl-5-(2-carboxyphenyl)formazan (22), in which all three rings are capable of supporting groups that increase the compound s reactivity and solubility. 

Metal-Complex (Formazan) Dyes. The hydrazone from 2-carboxyphenylhydra-zine-4-sulfonic acid and benzaldehyde is suspended in water and then dissolved by adding aqueous sodium hydroxide to obtain pH 6.5 -7.0. This solution is added to the aqueous diazonium salt solution obtained from a typical aqueous diazotiza-tion of 4-(2-sulfooxyethylsulfonyl)-2-aminophenyl-6-sulfonic acid. The mixture is then dripped into an aqueous solution of copper sulfate, while the pH is maintained with soda at 5.5 - 6.5. After complete coupling the pH is adjusted to 1 with concentrated hydrochloric acid. The strongly acidic solution is then neutralized with alkali to pH 5.5. The copper - formazan complex is salted out along with sodium chloride, filtered, washed with dilute aqueous sodium chloride solution, and dried. A dark powder results which gives a dark blue solution in water. It consists of an electrolyte-containing powdered sodium salt of the acid 25 ... 

Synthesis of the copper complex31 [167780-70-3] (H, Na salt) involves coupling of a diazonium compound with a hydrazone [54] 2-(3-amino-4-hydroxyphe-nylsulfonamido)chlorobenzene is dissolved in hot water, to which dilute NaOH solution is then added. After addition of sodium nitrite, the solution is cooled to -5 °C and then added to a well-stirred mixture of HC1, water, and ice. The diazonium salt suspension is neutralized with NaHC03 and combined with the weakly acidic solution of the hydrazone formed with 2-hydrazino-5-sulfobenzoic acid and benzaldehyde in water. The reaction mixture is kept at 0-10 °C, and at pH 10-12 by dropwise addition of diluted NaOH. When the coupling is complete, the pH of the formazan solution is reduced to 8 with HC1, a dilute aqueous solution of copper tetraaminosulfate is added and the solution is stirred for several hours. The copper complex 31 is precipitated at 85-90 °C with NaCl, then filtered and dried. The resulting powder colors wool in clear, fast blue tones. 

Again, similar to the simple formazans (5), those of the ozone-oxidized polysaccharides readily form complex salts with heavy metals. The probable structure of a copper complex obtained from the formazan of ozone-oxidized cellulose is ... 

A new field in which to apply formazan complexes has been opened up by a patent which utilized, in wool dyeing, the copper complexes of formazans containing hydroxyl or carboxyl groups in the ortho position. 

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. 

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