Лако-красочные материалы — производство

Formazans can be characterized as tautomeric structures 178 and 179. Schiele proposed that, in some cases at least, formazans are better represen­ted by the delocalized structure 180 implying coplanarity among substitu­ents.301302 1,3,5-Triphenylformazan can be isolated in two forms; the red form is assigned to the tautomeric structure 178 or 179 and the yellow form is […]

The physical and chemical properties of formazans have been reviewed in detail.1,2 In this discussion only those properties that directly or indirectly affect the choice of a tetrazolium salt as a leuco dye will be discussed. Spectral, acid-baser, edox, and metal complexing properties will be stressed. 3.5.1. Physical Properties Formazans are solids with relatively low […]

The methyl hydrogens in 1,3,5- and 1,4,5-trimethyl tetrazoliums, as well as the proton on C-5 in 2,3-disubstituted tetrazoliums are acidic, and can be abstracted with butyl lithium.289,290 Tetrazolium methylides, e. g., the dicyano derivative (143), and the phenacyl compound (171, R = Ph, R’ = Me) are known.291 The latter undergoes an unexpected thermal cyclization […]

Electrochemical methods have been used extensively to elucidate the mechanism of reduction of tetrazolium salts. In aprotic media, the first step is a reversible one-electron reduction to the radical 154 as confirmed by ESR spectroscopy.256,266 As shown in Scheme 26, this radical can then dispro­portionate to the tetrazolium salt and the formazan anion (166) or […]

This is by far the most important reaction of tetrazolium salts and accounts for the bulk of their many applications. A large variety of reagents can reduce tetrazolium salts, e. g., 53 to formazans, e. g., 51. Ascorbic acid, hydrazine, and hydroxylamine have been recommended for the preparation of formazans from tetrazolium salts.245 Stronger reducing […]

Tetrazolium salts are resistant to oxidation, but substituents on the ring can undergo oxidation. For example, 2-(4-hydroxyphenyl) tetrazolium (158) reacts with permanganate to give the tetrazole 160 via 159 (Scheme 23) 205,208,21 1

Solutions of tetrazolium salts, e. g., 53, have been reported to both become colored and bleached under the influence of both UV and visible light. Several workers have attributed this phenomenon to photoreduction to the corresponding formazan (51) and the formation of a fluorescent colorless compound (152) through photooxidation.240- 243 The reduction of 152 under […]

Tetrazolium salts are unstable in basic solutions yielding intense colors. This reaction is still little understood.233,234 In the reaction of 2,3,5- triphenyltetrazolium with hydroxide, it is postulated that a hydroxide ion is involved first as a counterion later leading to the hypothetical A-hydroxy — formazan (147).229 Weiner studied the kinetics of this reaction and identified […]

There have been very few systematic studies of the electronic spectra of tetrazolium salts. Generally, they have strong UV absorption maxima at 240 — 280nm.224 The introduction of electron-donating substituents on the phenyl group at the 2-position leads to a red-shift which extends further on the introduction of an electron-withdrawing substituent in the phenyl group […]

IR spectroscopy has been utilized to demonstrate the existence of isomers for 2,3,5-triaryl-substituted tetrazolium salts.203 In a systematic study, Arnold and Schiele list and assign all of the vibrational frequencies of 33 triaryl tetrazolium perchlorates.221 Of particular interest are the ring frequencies. Only one of the carbon—nitrogen frequencies is dependent on substitution. For example, C=N1 […]