Formazan 1.5- diaryl

Ethyl formate34,52 or orthoformate5 3,54 reacts with two equivalents of phenylhydrazine to yield 1,5-diphenylformazan (11) the reaction takes place under acidic conditions and involves an oxidation. Under basic conditions, ethyl nitrate reacts at the methylene position to yield 3-methyl-1,5-diphenylformazan (37) which can also be obtained from the reaction of phenyl-azoethane (38) with isoamyl nitrite (Scheme 4).8,68 Aryl hydrazines react with a variety of s-triazines (39) to yield 1,5-diaryl formazans with hydrogen, methyl, or phenyl groups in the 3-position as in 40 (Eq. 6).56 Hydrazines have also been reported to react with benzotrichloride55,658 and sym-diamino tetrazine659 to yield formazans. 

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... 

Bis-1,5-diaryl formazans generally absorb at longer wavelengths than mono formazans. The absorption maxima depend on the linking group. Formazans 188—191 (X = H) absorb at 485,470, 520, and 572 nm, respectively. The absorption maxima are also influenced by substituents. The formazan 190 (X = C02Et) absorbs at 510 nm whereas 191 (X = Me, OMe) absorbs at 585 and 606 nm, respectively.12,13 The absorption maximum of 192 shifts from 572 (R = H) to 585 and 602nm (R = Me, OMe), respec-... 

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