Formazans amidrazones

Diaryl carbazides and thiocarbazides, e.g., 43, can be oxidized at alkaline pH to yield C-hydroxy or C-mercapto formazans (44) (Eq. 8).68,129 The replacement of C-halo formazans is considered to be a better method60 for the preparation of 44. A class of cyclic formazans (45) can be obtained by air oxidation of amidrazones (46) (Eq. 9) 9,73,101,102 jhough this is formally a formazan, there are no reports of its oxidation reactions. In a... 

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 agents such as ammonium sulfide, sodium amalgam, sodium dithionite, and catalytic hydrogenation can further reduce the formazans to the amidrazones, e.g.,... 

As discussed in Section 7.4.2.5, the reduction of tetrazolium salts to formazans often results in further reduction products. As seen in Scheme 24, reduction of formazans with ammonium sulfide leads to the hydrazidine 161. The reduction can proceed further eliminating an arylamine, yielding an amidrazone, e.g., 162.364 By contrast, alcoholic hydrogen sulfide attacks... 

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)]. 

The use of 6-membered ring systems as sources of amidrazones to be converted into triazoles is relatively rare the case of 1-aminoadenine (Scheme 91) has already been mentioned. Transformations of 4,6-dihydrazinopyrimidine, hydrazines formed from haloaminopyridazine (81 HC(37)l, p. 8) and 1,2,4-triazines (8lHC(37)i, pp.409,424,488) all involve amidrazone intermediates cyclized to triazoles with the acyl function derived from the original ring. For instructive examples of preparative links between tetrahydrotetrazine, formazans and 1,2,4-triazoles, see Scheme 120 (81KGS694). 

Tetrazolium-Salze werden z.B. durch Sulfide zu Formazanen reduziert, mit den star-keren schwefelhaltigen Reduktionsmitteln (s. u.) bilden sich Amidrazone oder Hydra-zidine (s.ds. Handb. Bd. X/3, S. 674). Formazane ihrerseits werden durch Ammonium-sulfid, Natriumdithionit oder Thiole zu Amidrazonen und Hydrazidinen reduziert, wobei der Endpunkt der Reduktion von der Substitution am Formazan-Kohlenstoff abhangt (s.ds. Handb. Bd. X/3, S. 689). 

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