Azophenols

The azo-compounds are usually very stable, and can be directly chlorinated, nitrated and sulphonated. On vigorous reduction the molecule splits at the azo group to give two molecules of primary amines, e.g. bcnzene-azophenol gives PhNH2 and p-HOC H NHa. 

Dyes (11) from azophenols exist totally in the azo form8 whereas dyes (12) from heterocyclic couplers such as pyrazolones8,11 and acyclic couplers such as acetoacetanilides8 12 (13) exist totally in the hydrazone form. Dyes (14) derived from amino couplers exist in the azo form.8 However, as described above, all these dyes will exist predominantly in the azo form in the derived metal complexes. 

Lee DH, Lee KH, Hong JI (2001) An azophenol-based chromogenic anion sensor. Org Lett 3 5-8... 

HadZi used IR spectroscopy to study some azophenols and azonaphthols (112). The phenylazophenols were found to be phenolic in the solid state. On the other hand the molecule of 4-phenylazo-l-naphthol is present in the crystal as the hydrazone tautomer. Had2i suggested that in l-phenylazo-2-naphthol and 2-phenylazo-1 -naphthol both tautomers are present. Similar suggestions have been made by others (113,114). 

As for V(III), trigonal prismatic complexes, and trigonally distorted octahedral complexes are not uncommon for V(IV) [56]. The ligand set exerts a stronger influence on the redox potentials, whether the coordination geometry is octahedral or trigonal prismatic, at least to a first approximation. A series of compounds made with tridentate and tetradentate ligands with N- and O-donor atoms such as the azophenol derivative shown in Fig. 8 has both reversible oxidations and reductions. 

Dihydroxyazobenzene and Derivatives. See under Azophenol (Azodiphenol) in Vol 1, pp A657-A658. Its nitrated derivative Hexanitrodihydroxyazobenzene was examined during WWII from the point of view of its utilization as a military expl, but was found to be rather expensive to prepare Ref A.H. Blatt F.C. Whitmore, A Literature Survey of Explosives , OSRD Rept 1085 (1942)... 

Azophenol Azodiphenol or Dlhydroxyozo-benzene (called Dioxy-azobenzol or Azophenol in Beil) HO-QH NrN-QlVOH, mw 214.22, N 13-08%. Three isomers are described in the literature o,o -azophenol... 

H0(N02)2.C8H2.N N-CeH2(NO2)1OH mw 394.22, N 21.32% crysts (from glacial acetic acid), mp 261-2° with decompn (Ref 3). This compd was first prepd by Robertson (Ref 2) by nitration of tt-p-azophenol in acetic acid soln with a slight excess of HNOs In the same solvent. After recrystn from hot acetic acid, yel crysts melting sharply at 230°... 

N 24.78%. Brn amor pdr, dec 176-180, deflgr ca 275° easily sol in ale, AcOH acet diffc sol in hot w nearly insol in benz. Was prepd by reduction of azopicric acid(hexanitro-azophenol) with NaSH in w Refs l)Beil 26, [61] 2)K.Elbs O.H.Schaaf,... 

Reaction LXXIV. (b) Transformation of Azoxy Compounds to Azophenols. Azoxy compounds (see Reaction CLXX.) are converted by cone, sulphuric acid into p-hydroxyazo compounds (B., 13, 525). 

Extension of the NMR studies described in Section 58.2.3.3(i)(b) to the compounds (136 R = N02 and R = Bu ) led the authors to conclude that one Na- and two No-coordinated cobalt complexes were produced. These were assigned the partial structures (137), (138) and (139), which involve coordination of the ligand in its azo form and in the two alternative hydrazone forms. In general (Section 58.2.3.2), azophenols exist exclusively in the azo form and serious doubts must exist regarding structure (139). Similarly, in view of the reported equilibration between the various isomers in solution, assignment of discrete tautomeric structures must be open to question. As-... 

Azophenolates, in Ru and Os half-sandwich rj6-arenes, 6, 525 Azoxy complexes, ortho-metallated, liquid crystals, 12, 253... 

Yellow Dyes. A yellow D2T2 dye is probably the easiest to obtain both in terms of color and properties. The leading transfer-printing yellow dyes for textiles, such as quinophthalones and azophenols, are inadequate, as are typical photographic yellows such as azamethines. Two of the most widely used dye classes are methine (12) and especially azopyridones (13) [7,11,12],... 

Very recently it has been shown that treatment of the double salt of zinc chloride and p-hydroxybenzenediazonium chloride with ethyl alcohol leads to phenol (38% yield) and p, p -azophenol (ca. 60-66% yield).41... 

It appears, therefore, that in this case the primary decomposition product is phenol and that by coupling with undecomposed diazonium salt it is converted into the azophenol. Addition of zinc oxide to the reaction mixture raises the yield of phenol to 60% while that of the azo compound falls to approximately 30%. 

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