Aminophenols, diazotization

Figure 3. Influence of the diazotization temperature on the reaction of 4-aminophenol. [Diazotization conditions 4-H0C6H4NH2/NaN02/HF (5 5.1 900), ratio (HF/HF + pyridine) 0.86, 30 min. Dediazoni-ation conditions 140°C, 1 h]93...

Acid YeUow 23 (31), commonly known as Tartraziae, stiU maintains sales of nearly 0.5 million /yr ia the United States. It was first discovered ia 1884 and is made by coupling equimolar quantities of diazotized sulfarulic acid to 3-carboxy-l- -sulfophenyl)-5-pyrazolone. Other monoazopyrazolone dyes of commercial importance iaclude Acid YeUow 17 (32) (sulfarulic acid — l-(2,5-dichloro-4-sulfophenyl)-3-methyl-5-pyrazolone and Acid YeUow 40 [6372-96-9] (33) (Cl 18950) (p-aminophenol l-(4-chloro-2-sulfophenyl)-3-methyl-5-pyrazolone) foUowed by esterification of the phenoUc hydroxy group with -toluenesulfonyl chloride. 

It was previously mentioned in Section 1.2 that the products of diazotizing o- and /7-aminophenols exist in neutral aqueous solutions as zwitterions (1.7 b) which are mesomeric with the corresponding quinone diazides (1.7 a). They can therefore be... 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

For many decades intramolecular O-coupling was considered not to take place in the diazotization products of 2-aminophenol and its derivatives (for a contrary opinion see, however, Kazitsyna and Klyueva, 1972). The compounds were assumed to be present as one structure only, which can be represented as a mesomer of a phenoxide diazonium zwitterion 6.63 b and a diazocyclohexadienone 6.63 a (see reviews by Kazitsyna et al., 1966 Meier and Zeller, 1977 Ershov et al., 1981). In IUPAC nomenclature 6.63 is called 1,2-quinone diazide, in Chemical Abstracts 6-diazo-2,4-cyclohexadien-one (see Sec. 1.3). More recently, however, Schulz and Schweig (1979, 1984) were able to identify the intramolecular product of O-coupling, i.e., 1,2,3-benzooxadiazole (6.64) after condensation of 6.63 in vacuo at 15 K in the presence of argon (see Sec. 4.2). 

The properties of the diazotization product of 2-aminothiophenol are completely different from those of 2-aminophenol. In the reaction shown in Scheme 6-44 the diazo-thiophenolate (6.66) is not detected at all. The benzo-l-thia-2,3-diazole (6.67) is the stable product. A comparison of spectral data for diazophenoxide (6.63), benzo-l-oxa-2,3-diazole (6.64), and benzo-l-thia-2,3-diazole (6.67) is given in Section 4.2. The l-thia-2,3-diazole structure was first postulated by Le Fevre et al. (1954) on the basis of infrared spectra. 

A compilation of some 240 examples in the book by Ershov, Nikiforov and de Jonge443 demonstrates, however, that the most frequently used method is diazotization, applied to 2- or 4-aminophenols in the same or a similar way as described in Section II.A. It may be recalled that the very first diazotization (Griess, 1858) was carried out with an aminophenol derivative. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3) so-called neutral diazotization or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. 

Recently, the substituent effect on the diazotization of substituted 2-aminophenols was studied53 in aqueous hydrochloric acid solution. When the substituent is strongly electron-withdrawing, such as a nitro group, the diazotized product deprotonates and forms a substituted 1,2-benzoquinone-l-diazide which usually precipitates. 

Cram and Day 57> successfully synthesized a quinone of [2.2]para-cyclophane by coupling the phenol 148 with diazotized sulphanilic acid to give 149. Reduction of 149 gave the unstable aminophenol 150 on oxidation with ferric sulphate 150 afforded the quinone 30 in 68% overall yield. 

Glowiak studied the stability of the four diazophenols (59-62), which he prepared from the diazotization of the corresponding aminophenols. It was noted that (61) and (62) show higher chemical stability than (59) and (60) the latter compounds were postulated to have a quinonoid structure rather than a zwitterionic diazophenol structure. 

Glowiak [20] examined the properties of the diazotization products of numerous nitro derivatives of o-aminophenol, viz. ... 

HO.C6H4.N]2.Crp7 N 12.23% yel crysts mp - expl ca 134° was prepd by Me ldola 8e Eynon (Ref 2) on diazotizing p-aminophenol with Na nitrite in sulfuric acid, followed by treatment with Na dichromate Refs 1) Beil - not found 2) R. Meldola ... 

Diazotization of 2-aminophenols followed by reaction with diazomethane gives 1,3,4-benzox-adiazines (Scheme 39) the initially formed 2//-isomers readily tautomerize to the more stable 4Z/-isomers (70CB331). 

Dealkylative and oxidative coppering and subsequent demetallation in aqueous mineral acids are technical processes to prepare o.o -dihydroxyazo compounds, which are not available from o-aminophenols by diazotation and coupling reactions. 

C.I. Acid Yellow 76, 18850 [6359-88-2] (14), is obtained by coupling diazotized 4-aminophenol onto the pyrazolone component and then esterifying with -toluene-sulfonic acid chloride in an alkaline medium. The toluenesulfonic ester group substantially improves the fastness to milling and makes the shade obtained largely independent of pH the lightfastness is not quite as good as that of C.I. Acid Yellow 17. 

In the synthesis of the unsymmetrical 1 2 cobalt complex 18 [68928-31-4] [30], the 1 1 cobalt complex 17 and the azo dye made by coupling of 1-acetoacetyl-amino-2-ethylhexane with diazotized 2-aminophenol-4-sulfonamide are intro-... 

Iodophenol was first obtained as a by-product of the action of iodine on salicylic acid in alkaline solution or by heating iodo-salicylic acid.1 It has also been obtained by the action of iodine on phenol in alkaline solution2 or in the presence of mercuric oxide,3 or by the action of iodine monochloride.4 It is best prepared by the diazotization of -aminophenol and replacement of the diazonium group by iodine 5 although it has also been obtained from />-iodoaniline by diazotization and replacement of the diazonium group by hydroxyl.6... 

Nitroderivatives of orf/to-aminophenole on diazotization form the corresponding orf/todiazophenols, which readily undergo cyclization into 1,2,3-benzoxadiazoles (Scheme 2.82) [513-518],... 

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