0-Aminophenol

The direct replacement of a phenolic hydroxyl group by the amino group is relatively difficult m the benzene series, requiring high temperatures, although it takes place somewhat more readily in the case of the naph-thols. If, for example, resorcinol and ammonia alone are heated under pressure, a high reaction temperature is required, and the yield of m-aminophenol is poor. If, however, ammonium chloride is present,9 the reaction may be carried out at a lower temperature and the yield is more satisfactory. 

of resorcinol, 120 g. of ammonium chloride, and 400 cc of 10 per cent aqueous ammonia are heated in an autoclave in a bath the temperature of which is 220°, the heating being continued for 14 hours after the pressure reaches a constant value The yields are smaller if the heating is carried out at a lower temperature or for a shorter period and are not improved 

Owing to the fact that sodium arsenite is a reducing agent, the reaction does not proceed quantitatively, some of the diazo compound being reduced with formation of nitrobenzene  

M Instead of Expt, V B the nitro acid may be reduced with ferrous sulfate ana alkali according to /. Am. Chem. Soc. 40, 1583 (1918), yielding o-arsanilic acid. 

Either anthranilic acid itself, or acetanthramlic add, the intermediate product in the preparation of an-thranilic acid from, o-acet-toluidide, may be used for the esterification, since alcoholic hydrochloric acid hydrolyzes, or rather alcoholyzes, the acetamino group. 

Experiment.—Test the reducing effect of phenylhydroxylamine by dissolving material on the point of a knife in 2 c.c. of warm water and adding to the solution a few drops of ammoniacal silver nitrate solution. 

Experiment. — Isomeric change of phenylhydroxylamine to p-aminophenol.1 The base (2-2 g. 002 mole) is added in small portions to a mixture of 10 c.c. of concentrated sulphuric acid and 30 g. of ice, externally cooled by more ice. 

The solution is diluted with 200 c.c. of water and boiled until a sample, when mixed with dichromate solution, no longer smells of nitrosobenzene but of quinone (ten to fifteen minutes). To the cooled solution 2 g. of dichromate dissolved in water are added, a downward condenser is attached to the flask containing the mixture, and steam is passed through. The quinone is carried over with the steam. On the mechanism of its formation in this reaction compare p. 310. Test the residue in the flask for ammonia. 

The change which arylhydroxylamines undergo by the action of mineral acids, especially when warm, is worthy of special note. If the position para to the NHOH-group is free, a rearrangement takes place to the isomeric p-aminophenol, e.g. in the case of phenylhydroxylamine according to the equation  

A process for the direct reduction of nitrobenzene to -p-ammophenol, an important intermediate for the production of dyes, depends on the above interesting transformation. Nitrobenzene in alcoholic solution is mixed with concentrated sulphuric acid and electrolysed with a lead cathode. This process proves that phenylhydroxylamine is also an intermediate in the reduction of nitrobenzene in acid solution, as was mentioned above. Here, as a result of the rapidity of the rearrangement which takes place, it is not converted into aniline. 

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Bright yellow needles m.p. 45 C, b.p. 2 4°C. Prepared together with 4-nitrophenol by careful nitration of phenol. Sodium sulphide reduces it to 2-aminophenol which is used in dyestuffs and photographic processes. 

Aminophenols and their derivatives are of commercial importance, both in their own right and as intermediates in the photographic, pharmaceutical, and chemical dye industries. They are amphoteric and can behave either as weak acids or weak bases, but the basic character usually predominates. 3-Aminophenol (2) is fairly stable in air unlike 2-aminophenol (1) and 4-aminophenol (3) which easily undergo oxidation to colored products. The former are generally converted to their acid salts, whereas 4-amiaophenol is usually formulated with low concentrations of antioxidants which act as inhibitors against undesired oxidation. 

The aminophenols are chemically reactive, undergoing reactions involving both the aromatic amino group and the phenoHc hydroxyl moiety, as weU as substitution on the benzene ring. Oxidation leads to the formation of highly colored polymeric quinoid stmctures. 2-Aminophenol undergoes a variety of cyclization reactions. 

Acylation. Reaction conditions employed to acylate an aminophenol (using acetic anhydride in alkaU or pyridine, acetyl chloride and pyridine in toluene, or ketene in ethanol) usually lead to involvement of the amino function. If an excess of reagent is used, however, especially with 2-aminophenol, 0,A/-diacylated products are formed. Aminophenol carboxylates (0-acylated aminophenols) normally are prepared by the reduction of the corresponding nitrophenyl carboxylates, which is of particular importance with the 4-aminophenol derivatives. A migration of the acyl group from the O to the N position is known to occur for some 2- and 4-aminophenol acylated products. Whereas ethyl 4-aminophenyl carbonate is relatively stable in dilute acid, the 2-derivative has been shown to rearrange slowly to give ethyl 2-hydroxyphenyl carbamate [35580-89-3] (26). 

Condensation Reactions. Condensation of substituted ben2aldehydes with 2-aminophenol in the presence of a catalyst (aluminum, iron,... 

Insoluble red lakes are formed as by-products which decrease yields when 2-nitrophenol [88-75-5] is reduced with iron. Consequendy, the iron reduction of this nitro compound to 2-aminophenol is of minor industrial importance today. 

More specifically, 2-aminophenol can be detected in solution using an iron(II) sulfate—hydrogen peroxide reagent (94). 3- Aminopheno1 has been analyzed colorimetrically by oxidation in base and subsequent extraction of a violet quinoneimide dye (95). A colorimetric method using... 

The potentiometric micro detection of all aminophenol isomers can be done by titration in two-phase chloroform-water medium (100), or by reaction with iodates or periodates, and the back-titration of excess unreacted compound using a silver amalgam and SCE electrode combination (101). Microamounts of 2-aminophenol can be detected by potentiometric titration with cupric ions using a copper-ion-selective electrode the 3- and... 

GK [10343-58-5] (S ) (Cl Acid Yellow 99 Cl 13900) (4-nitro-2-aminophenol —> aceto acetanilide) and Palatine FastRedBEN [6656-02-6] (59) (Cl Acid Red 214 Cl 19355) (2-amiao-6-nitroplienol-4-sulfonic acid — 2,4-dihydroxyquiQoline). 

Aminophenol [95-55-6] M 109.1, m 175-176 , pKj 4.65, pKj 9.75. Purified by soln in hot water, decolorised with activated charcoal, filtered and cooled to induce crystn. Maintain an atmosphere of N2 over the hot phenol soln to prevent its oxidation [Charles and Preiser J Am Chem Soc 74 1385 7952]. Can also be crystd from EtOH. 

A number of azacrown compounds were reported by Lockhart and coworkers in 1973. In a typical case, 2-aminophenol was heated at reflux with an equivalent of tet-raethylene dichloride for 48 h. A mixture of the monoaza-15-crown-5 (5) and the mono-aza-12-crown-4 (4) shown in Eq. (4.4) were obtained. Structural assignments were based on H-NMR, IR and mass spectral data. 

The 1,5-benzoxazepinedione 1 is obtained from 2-aminophenol and the 5,5 -diphenyl ester of dithiomalonic acid in the presence of a catalytic amount of 4-(dimethylamino)pyridine.37... 

The amides formed from 2-aminophenols and 2-chloropyridine-3-carbonyl chlorides readily cyclize to pyrido[2,3-/>][l,5]benzoxazepin-5(6//)-ones under basic conditions, e.g. cyclization of 1 to give 2.41... 

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