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Formazan 3-substituted

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. [Pg.102]

As the reaction sequence of Scheme 12-38 can be stopped at the stage of the oo-methylglyoxal phenylhydrazone (12.78), it is possible to synthesize asymmetrically substituted formazanes (12.80, Ar = Ar ) by reacting acetone with one equivalent of a diazonium ion ArNJ under acidic conditions and then coupling the co-methyl-glyoxal phenylhydrazone with Ar NJ in alkaline solution. [Pg.335]

Formazane lassen sich durch milde Reduktionsmittel, u.a. auch durch Thiole zu Hydrazidinen und Amidrazonen reduzieren, wobei allein die Substitution am Forma-zan-C-Atom fur das Endprodukt verantwortlich ist (s.Bd. X/3, S. 689). [Pg.566]

Diazonium salts add to active methylene compounds, for example ethyl acetoacetate, to form an intermediate azo compound (22), followed by the addition of a second diazonium salt (under more alkaline conditions) to yield the tetrazene (23) which then forms a 3-substituted formazan (24)10... [Pg.212]

Aldehyde semicarbazones with two substituents on the terminal amino group (but not the hydrazino) (33) react with diazonium salts to yield N-carbamoyl-substituted formazans (34) (Eq. 4).47,48 A sulfonic acid deriva-... [Pg.215]

The earliest oxidations were effected with nitrous fumes and later with mercuric oxide and isoamyl nitrite.74 Lead tetraacetate in acetic acid is in many cases the reagent of choice, but the removal of by-products can present some difficulties.75 IV-Haloimides and amides in alcoholic solutions have been reported to yield essentially pure tetrazolium salts76 and have been found specially useful in the preparation of heteroaryl-substituted tetrazolium salt.77,78 The novel formazans 49 have been successfully oxidized to 50 using 7V-chloro succinimide (Eq. II).79 tert-Butyl hypo-... [Pg.219]

Wedekind and Stauwe" studied the oxidation of 3-substituted formazans and concluded that ease of oxidation depended on the steric effects of the 3-substituent. More recently, Hegoraty et al. 100 studied the reaction of formazans with bromine. It proceeds via an odd-electron species such as 52 favoring an electronic substituent effect (Scheme 5). The rate of reaction increases with electron-donating substituents. Similar conclusions have been reached using thalium(III) as the oxidant.101,102... [Pg.220]

Unsymmetrically substituted formazans form a complex mixture of valence tautomers and geometric isomers with different conformations. The tautomerism is further complicated when substituents on the aryl ring are... [Pg.257]

Formazans behave as weak acids as well as weak bases. Salts of formazans have been isolated.26,334,335 The acid dissociation constants of some substituted formazans have been determined from their solution spectra.336... [Pg.262]

Tables 15 and 16 show the absorption maxima of some metal complexes of benzothiazolyl-substituted formazans 230 and 231.283 The wavelengths are metal ion dependent, making formazans useful reagents for the identification of specific metal ions or the simultaneous determination of two ions. The wavelengths are much longer than those of the formazan anion (Table 14). The general trend for electron-rich substituents is toward a larger shift this is to be expected as it tends to enhance the aromatic character of the ring and increase the covalent character of the metal — nitrogen bond. The sharpness of the absorption band has been attributed to coordination to the heterocyclic nitrogen as in 232.57S... Tables 15 and 16 show the absorption maxima of some metal complexes of benzothiazolyl-substituted formazans 230 and 231.283 The wavelengths are metal ion dependent, making formazans useful reagents for the identification of specific metal ions or the simultaneous determination of two ions. The wavelengths are much longer than those of the formazan anion (Table 14). The general trend for electron-rich substituents is toward a larger shift this is to be expected as it tends to enhance the aromatic character of the ring and increase the covalent character of the metal — nitrogen bond. The sharpness of the absorption band has been attributed to coordination to the heterocyclic nitrogen as in 232.57S...
The position of the substituents is given according to IUPAC nomenclature using the prefixes 1-, 3-, and 5-. Formazans unsubstituted in the 1- and 5-positions and 1,5-dialkyl-substituted formazans are unknown. Aryl or heteroaryl groups are the most common 1,5-substituents. The 3- or meso position can be occupied by a variety of substituents (e.g., aryl, heteroaryl, H, OH, SR, halogen, N02, CN, and alkyl). [Pg.98]

Ester and cyano groups generally resist substitution by aryl azo groups and must first be hydrolyzed to produce carboxyl and carbonamide groups respectively, which can be more easily eliminated [62], Unsymmetrical formazans can be produced according to Scheme 2.15. [Pg.100]

Virtually every conceivable chromophore has been used in the synthesis of reactive dyes, including monoazo and disazo species, metal complexes of azo dyes, formazan dyes, anthraquinones, triphenodioxazines, and phthalocyanines. The product lines offered by the major dye producers in most cases feature comparable chromophores, differing primarily in the nature of the reactive systems and the particular substitution patterns adopted. [Pg.118]

According to Butler, acyclic systems other than imidoyl azides that may be cyclized to tetrazoles include substituted tetrazenes, some triazenes, and formazanes <1984CHEC(4)791, 1996CHEC-II(4)621 Examples of these reactions and of the corresponding products 6, 10, and 525-528 are shown in Scheme 75 <1996CHEC-II(4)621>. [Pg.382]

Among the first cell viability assays developed for HTS was the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] tetrazolium reduction assay (Mosmann 1983) that served as a milestone for this type of study. The assay offered a non-radioactive alternative to tritiated thymidine incorporation into DNA as a method of measuring cell proliferation. In many cases, the MTT assay can directly substitute for the tritiated thymidine incorporation assay (Figure 6.3). The MTT tetrazolium compound is prepared in a physiologically balanced solution, added to cells in culture, and incubated for approximately 4 hr. Viable cells convert MTT into an intensely colored formazan product that can be quantitated by recording changes in absorbance at specific wavelengths. [Pg.108]

Direct alkylation of 5-substituted tetrazoles is often the best method of obtaining simple 2,5-disubstituted tetrazoles. The 1,5-isomers, which are formed as competitive side products, are usually separated with ease by fractional crystallization or better by column chromatography on alumina or silica gel which gives excellent separations of most tetrazole isomers (8UCR(S)174). Another convenient synthesis of 2,5-disubstituted tetrazoles (241) is the formazan method (Scheme 31). By coupling aldehyde arylsulfonylhydrazones (240) with diazonium salts in basic solutions, compounds (241) may be obtained directly in yields of up to 78% (76BCJ1920). [Pg.834]


See other pages where Formazan 3-substituted is mentioned: [Pg.210]    [Pg.213]    [Pg.213]    [Pg.213]    [Pg.215]    [Pg.251]    [Pg.259]    [Pg.259]    [Pg.260]    [Pg.261]    [Pg.269]    [Pg.473]    [Pg.247]    [Pg.259]    [Pg.321]    [Pg.666]    [Pg.667]    [Pg.672]    [Pg.77]    [Pg.283]    [Pg.123]    [Pg.793]    [Pg.827]    [Pg.837]    [Pg.473]    [Pg.793]    [Pg.827]    [Pg.837]    [Pg.188]    [Pg.317]    [Pg.77]   
See also in sourсe #XX -- [ Pg.212 , Pg.213 , Pg.220 ]




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