Tetrazolium salts

The diazonium salts precursors can be aniline, o- and p-toluidine, o-and p-anisidine, o- and p-phenetidine. or 3-naphthy]amine. The resulting formazans are crystalline and inlensel> colored. They are soluble in organic solvents, giving a red-violet coloration that darkens to blue. Dehydrogeneration gives the corresponding tetrazolium salts, which are isolated as perbromides (Scheme 51. Table X-13). 

Tetrazolium iodide, l,3-dialkyl-5-phenyl-synthesis, 5, 815 Tetrazolium salts electrochemical reduction, 5, 73 hydrogen exchange, 5, 70 Tetrazolium salts, 2,3-diphenyl-5-oxide... 

Tetrazolium salts Formazan dyes are produced on reaction of [33]... 

Although the formation of tetrazolium salts of structure 92 by the oxidation of formazans under acid conditions has been known for many years, it is only recently that the quatemization of 1,5-disubstituted... 

NADPH-diaphorase activity is the ability of an enzyme to reduce soluble tetrazolium salts to an insoluble, visible formazan. This activity is being used by many laboratories to localize NO synthase histochemically. 

Tetrahydrocannabinol (= THC)-11-carboxylic acid 290 Tetrahydrocortiso 221 Tetrahydrocortisone 221 Tetrahydrosteroids 222 Tetrazolium salts, reduction 61 Thalidomide 45 -, hydrolysis products 45 Thiabendazole 307, 308 Thiamine 235, 236, 397 Thickening agents 179 Thin-layer chromatography, advantage 5 -, numbers of publications per year 6 Thiobarbiturates 45,66 Thiocarbamide derivatives 322 Thiocarbamides, N -ary I-N -benzenesulfo-nyl- 248,249 Thiochrome 395... 

A colorometric assay based on the tetrazolium salt XTT was used to evaluate the cytotoxity of the compounds. 

Tetrazolium salts are an important class of leuco dyes that have found a wide range of applications. They are unique among the synthetic leuco dyes in that the colored form of the dye is the reduced form rather than the oxidized form. There are at least three extensive reviews on tetrazolium salts and the corresponding formazan dyes1-3 and one textbook.96 This chapter will describe some recent developments as well as some of the material covered in these reviews. 

Tetrazolium salts to a large extent are prepared from the corresponding formazans and to a lesser extent from tetrazoles. Therefore, synthetic methods for both formazans and tetrazoles will be discussed. Also discussed will be some properties of formazan dyes that influence the choice of the tetrazolium salt for any particular application. 

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... 

In general, tetrazolium salts are prepared by (a) oxidation of formazans and (b) alkylation of tetrazoles. Therefore, synthetic methods for formazans and tetrazoles are discussed first, followed by some direct and miscellaneous methods. 

A variety of oxidizing agents have been used to effect the transformation of formazans to tetrazolium salts. The choice of the reagent is still empirical and depends on the solubility properties of the formazan as well... 

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-... 

Electrochemical oxidation has also been reported to result in good yields of tetrazolium salts.97,98 Treatment of formazans with boron trifluor-... 

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