Formazan derivative

The chemical oxidation of 1,3,5-triarylformazans to tetrazolium salts was first accomplished in 1894 [127], Almost no attention was given to these compounds for about 50 years after their discovery. This situation began to alter markedly because of the application of tetrazolium salts in histochemical, pharmacological, and other biomedical research areas [128]. Specifically, the tetrazolium salt is reduced to a colored formazan derivative by reducing enzymes found only in metabolically active cells. Anodic transformation of for-mazans to tetrazolium salts was performed in acetonitrile solution using cotrolled potential electrolysis [17,129], In our view this reaction could be considered as a method of choice for the preparation of tetrazolium salts. The products were obtained in high yield and the electrolysis can be performed in a divided cell under constant current and decoloration of the solution indicates the end point of the reaction. Recently the anodic oxidation of formazans to tetrazolium salts was performed successfully in aqueous ethanol solution [130]. 

Formazanes, derivatives of heterocyclic carboxylic acids 92MI12. 

Finally, as detailed in reference 1, p.739 various ortAo-metallated complexes have been generated from the ligand o-CH2=CHC6H4PPh2 (SP) e.g. reaction of [RuCl2(CO)2(SP)2] with boiling 2-methoxyethanol gives, as the major product [Ru(o-CHMeC6H4PPh2)Cl(CO)(SP)] (200). Other more complex products from this reaction are discussed in reference 1489. See Section 45.5.4.6.v for an example of a cyclometallated formazan derivative. 

From ozone-oxidized sugar alcohols no formazan derivatives have yet been isolated in which the primary alcoholic hydroxyls, presumably present at both ends of the molecule, have oxidized to aldehydes. However, bisformazans, conspicuous for their capacity to crystallize and their insolubility in water, have been successfully prepared by other means (13). 

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. 

Prepared in situ by diazotization of p-aminobenzoic acid with sodium nitrite in an acid medium, the reagent reacts with an active methylene compound (at pH < 6 to avoid formation of a formazan derivative) to give a p-carboxyphenylhydrazone, which can be titrated with 0.1 )VN aOH as a monobasic acid. 

Syntheses of amino-alditol derivatives are covered in Chapters 18 and 19, and the introduction of a 2-acetamido-function into a sugar formazan derivative is covered in Chapter 10. 

Amin (2001) reported a colorimetric method for vitamin E in pure form and multivitamin capsules based on the reduction of tetrazolium blue to formazan derivative by vitamin E in alkaline medium. The reaction mixture was incubated at 90 2 C for 10 min and the absorbance of the reaction product was monitored at 526 nm with relative standard deviation of 0.7%-1.5%, a limit of detection 0.012 mg/E and sample throughput of approximately 6/h. The reduction of tetrazolium blue to formazan derivative requires 3 h at room temperature and the color developed was stable for 3 h. EDTA was added to sample solution for masking any metal ions during analysis. 

Lamontagne, P Maion, G Page, M. Cytotoxicity testing using a soluble tetrazolium formazan derivative. Cell. Pharmacol. 1994, 1, 171-174. 

Bulka et al. (43) have demonstrated the electrophilic reactivity of selenazoles possessing an hydrazonc in the 2-position and nonsubstituted in the 5-position toward diazonium salt to give 5-phenylazo derivatives preferentially. For example, the main product of the coupling of 2-benzylidene hydrazino-4-phenylselenazole with diazo-o-phenetidine is the 5-(o-ethoxyphenylazo)-selenazole (Scheme 371 ruby red prisms, m.p. 206°C. yield 67"o). A formazan is obtained as by-product. (See Section III.6) (43). 

Despite the inconveniences, a certain number of studies have been carried out, particularly concerning dyes containing azomethine groups. Such as hydrazones, pyrazolones, formazans, and selenazoles quinoids. Saturated heterocycles, that is, selenazolines and selenazolidines. have also been tackled. Selenium derivatives for pharmacological or physiological applications are little developed by comparison with their thiazole homologs. 

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. 

The editors note with regret the passing of Laszld Mester on February 23, 1986. Mester worked extensively on hydrazine derivatives of sugars, and he contributed a notable article on the formazan reaction in Volume 13 of this series. 

Tetrazolium salts are derivatives of the H-tetrazole (1) or 2H-tetrazole (2). The CA numbering systems for tetrazoliums and formazans are shown in 3 and 4. It should be noted that the carbon atoms in 3 and 4 are... 

Absorption spectra of formazans have been studied in detail. Almost all formazans exhibit UV/visible spectra between 300 and 600 nm.1,2,12,13,40,62,325 326 The absorption maxima are very sensitive to substituent effects. For example, the 1,5-diphenyl formazan 185 when X is hydrogen, methyl, phenyl, cyano, and mercapto shows a band at 420, 410, 470, 504, and 590nm in ethanol, respectively. The 3-chloro derivative 186 when X is hydrogen, iodine, bromine, chlorine, and fluorine has a band at 433,433,430,421, and 417 nm, respectively. Table 13 shows the influence of substituents on the absorption maxima in the trisubstituted formazans 3. Table 14 shows the influence of substituents on the absorption maxima of... 

In the reaction of heterocyclic amidrazones with DMAD, condensed 1,2,4-triazinones have been reported. Cherkasov et have studied the reaction of the formazan (141) with DMAD and have shown that the 1,3,4-dihydrotriazine derivative (142) and a 1 1 adduct (143) are formed in this reaction [Eq. (23)]. 

ArN-NCRNNHAr by M. Ragno S. Bruno who prepd various nitro derivs [Gazz Chimltal 76, 485—99(1946) and CA 41, 6542(1947)]. For instance, the compd PhN=NC(CN)= NNHPh may be called N,N -Diphenyl-C-cyano formazan or N, N7-Di phenyl-formazylcyanide. Some of the formazan or formazyl derivs give expl salts while others form tetrazoles or other ring compds Note C Metby I formazan is called Acetazidin or Azidin in Beil 2, 4, but the name azidin has been suggested for the radical NgC(—)=NH, which is entirely different... 

Blue dyes are derived from anthraquinone, phthalocyanine, or metallized formazan. See also Anthraquinone (Figs. I and 2). There are also oxazine and thiazine dyes reported (Fig. 2). 

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... 

As far as dyes are concerned, chelates of type Cb are termed 1 2 or symmetrical 1 2 metal complexes if the two tridentate ligands are equal, and mixed or unsymmetrical 1 2 metal complexes in the other case. Chelates of type Bb represent 1 1 metal complexes. The types Cb and Bb include, in general, azo and azo-methine metal complex dyes, whereas chelates of the quadridentate types Ac and Be are derived predominantly from formazan and phthalocyanine chromophores. 

Formazan dyes are closely related to azo dyes and are derived from the following basic structure ... 

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