Diazotization of aminophenols

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... 

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. 

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. 

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. 

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). 

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-... 

Polar yellow 5G is prepared by condensing p-chloro-m-sulfophenylhydrazine with acetoacetic ester, and coupling the resulting pyrazolone with diazotized p-aminophenol in acetic acid solution. The alkali sensitive dye which is formed is treated at 70°C. with p-toluenesulfonyl chloride, in the presence of soda and 1 mole of sodium hydroxide, to esterify the hydroxyl group. This esterification makes the dye insensitive to alkali and, at the same time, fast to milling on wool. 

Carbena-cyclohexadienone (3). Photolysis or thermolysis of -quinone diazides (15) easily led to 3. The precursors of 3 are either />-aminophenols (14), -quinones (77) or anthrones (76). Diazotization of 14, Bamford-Stevens reaction of the tosyl-hydrazone of 77, or diazo-group transfer to 76 afforded the corresponding -quinonediazides 15 31-84)... 

Polymethylquinones and certain polycyclic quinones are prepared by the oxidation of aminophenols and their polycyclic analogs. The latter substances are readily obtained by coupling the corresponding phenolic compound with diazotized sulfanilic acid followed by a reductive cleavage of the azo compound. 

Certain nuclear substituents ortho to a newly formed diazonium group may interact to form a cyclic structure with or without retention of the nitrogen atoms. Such is the case in the diazotization of o-phenylene-diamine in aqueous solution, the product being 1,2,3-benzotriazole (81%). If the ortho substituent is an activated methyl group, an indazole is formed. Hydroxyl groups ortho or para to the diazonium group may interact to form internal condensation products called diazo oxides. These compounds may also form in the reaction of halo- and nitro-substituted aminophenols. 

Dichlorophenol has been prepared by the chlorination of phenol with chlorine gas in the presence of nitrobenzene and fuming sulfuric acid, by the decomposition of the diazotate of 2,6 dichloro-4-aminophenol, eind by the decarboxylation of 3,5-dichloro-4-hydroxybenzoic acid in quinoline or dimethyl-aniline. ... 

Isoamyl lutrite-Trlfluoroacetic add. For the diazotization of the weakly basic aminophenol (1), which is unstable in the presence of a trace of water, a solution... 

Sus and his co-workers179 have applied the Wolff-Schroter rearrangement to 0-quinone diazides, which are accessible by diazotization of o-aminophenols and subsequent treatment with alkali. When irradiated, the quinone diazides lose nitrogen and pass into ketenes by ring contraction the ketenes are isolated as acids since the reaction is always effected in water. 

The diazotization products of 2- and 4-aminophenols, -naphthols (etc.), possess a mesomeric (zwitterionic) phenolate-diazonium and quinone-diazide structure. We discussed these structures in the context of aromatic diazotization (Zollinger, 1994 Sect. 2.4) because the synthetic methods used are closely related to those used for aromatic diazonium salts. This is also the case for the diazotization of amino-di-, tri- and tetrazoles, which, in their neutral form, contain a heterocyclic NH group in the )8-position to the amino group. After diazotization, the NH group is very acidic. Following deprotonation the product corresponds to a heterocyclic diazoalkane. Similarly, the diazotization product of 4-(dicyano)methylaniline ((4-amino-phenyl)malonitrile) may lose the CH proton. This compound is, therefore, sometimes called a vinylene homolog of diazomalonitrile (Regitz and Maas, 1986, p. 205). 

Trihydroxyazobenzene was prepared by coupling diazotized p-aminophenol with resorcinol (100% excess) in the presence of sodium hydroxide. The product was purified by dissolving it in sodium hydroxide and reprecipitating with acid and finally by two crystallizations from 70% alcohol. 

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