Formazans amines

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). 

Carbonsaure-imid-ester Oder deren Salze werden durch Natriumboranat in neutralem Medium zu 0,N-Acetalen (s. S. 436 f.) (bzw. Aldehyden) Oder Aminen reduziert. Amidine und Imid-chloride gehen in Amine iiber, Formazane in Amid-hydrazone. 

In warm mineral acid, formazans (195) rearrange to a benzotriazine (196) eliminating an amine (Scheme 29).8,26 27 334 338 339 H owever, when R is methyl, phenylazo, or oxalyl, the main product is the phenazine 197 along with a trace amount of the benzotriazine.340 The mechanism of this reaction is not well understood.341 345... 

Anodic oxidation of azomethine, hydrazone, oxime, formazane, and semicarbazone structures has been used to initiate the intramolecular cyclization [119] under formation of heterocycles like triazoles [126,127], oxadiazoles [128,129], triazolinones [129], benzoxa-zoles [130,131], benzimidazoles [130,131], pyrazoles [132], indazoles [133], furoxanes [134], and tetrazolium salts [135] (see Chapter 18). Some of these reactions can be performed advantageously by indirect electrolysis using tris(4-bromophenyl)amin or 2,3-dihydro-2,2-dimethylphenothiazine-6(l/7)-one as mediators [119,136]. Two examples are given in Eqs. (19) and (20). 

Indirect oxidation with tris-(4-bromophenyl)amine or 2,3-dihydro-2,2-dimethylphe-nothiazine-6(l/7)-one transforms formazane to tetrazolium, semicarbazones to 2-amino-1,3,4-oxadiazoles, benzaldehyde 2-pyridylhydrazones to 5-triazolo[4,3-a]pyridinium compounds, and phenyl 2-pyridyl ketone phenylhydrazone to 1/7-1,2,3-triazolo[3,4-a]-pyridi-nium compounds [123]. 

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. 

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