4- Hydroxy-2-nitroaniline

Some impurities may be found under these GC conditions quinoxaline, phenazine, tetrahydrophenazine, nitroanilines, hydroxy anilines, chloronitrobenzenes, hydroquinone, diami-nophenazine, aminohydroxyphenazine 30 m DB-17 column, 100-275° at 6°/min. 

Apart from the chemistry of the 4-hydroxy derivative (see p. 126) relatively little investigation in this area has been conducted. Thiocoumarin-3-carbonyl compounds have proved to be effective precursors for the synthesis of the pharmaceutically useful 3-(2-benzimidazolyl) derivatives. Thus, on interaction of the 3-carboxamide with o-phenylenediamine or the 3-aldehyde with o-nitroanilines, the above benzimidazoles or their TV-oxides are formed. 

An amorphous preparation was made similarly from 2,3,4,6-tetra-O-acetyl-(2-hydroxy-D-galactal).9 It was noted that this preparation did not give the reactions reported by Helferich for the 5,6-anhydro derivative with pyrogallol, orcinol, aniline, and m-nitroaniline. However, it did give a voluminous, red-brown precipitate with phloroglucinol. 

SYNS 4-AMINO-2-NITROPHENOL C.I. 76555 FOURRINE 57 FOURRINE BROWTS PR FOURRINE BROWN PROPYL 4-HYDROXY-3-NITROANILINE NCI-C03963 o-NITRO-p-AMINOPHENOL OXIDATION BASE 25... 

Base-induced conversion of lV,iV-disubstituted-o-nitroanilines (59) into benzimidazole A/-oxides may occur provided that one of the carbon substituents can be removed subsequently (e.g. cyano or arylsulfonyl). The reaction products, however, may well differ from those obtained from the monosubstituted analogues, e.g. cyclization of lV-alkyl(or aryl)-iV-cyanomethyl-onitroanilincs gives not the 2-cyanobenzimidazole M-oxides, but the 2- hydroxy derivatives [148J. These processes do not seem to have great synthetic utility. 

Problem 24.2 In hich of the following compounds would you expect intramolecular hydrogen bonding to occur u-nitroaniline, o-cresol, o-hydroxybenzoic acid (salicylic acid), o-hydroxybenzaldchyde (salicylaldehyde), o-fluorophenol, o-hydroxy-benzonitrile. 

A. Takase, S. Sakagami, K. Nonaka, and T. Koga, Spectroscopic studies ofthe thermochromism of A-(2-hydroxy-4-methoxyberizylidene)4-nitroaniline, J. Raman Spectrosc. 24, 447-451 (1993). 

The synthesis of 2(2-hydroxy-5-methy lphenyl)2H-4 -vinyl-benzo-triazole was accomplished (31) by a sequence of reactions similar to those which gave 2H5V. The starting material for this synthesis was, however, not o-nitroaniline but 4-ethyl-o-nitroaniline. After diazo-tiation, the diazonium compounds were allowed to react with p-cresol the condensation product gave 2(2-hydroxy-5-methylphenyl)2H-4-ethyl-benzotriazole after reductive cyclization. This compound was acetyl-ated, brominated, dehydrobrominated, and hydrolyzed to 2(2-hydroxy-5-methylphenyl)2H-4 —viny1-benzotriazole. 

N-oxides of this type are accessible from o-nitroaniline-based syntheses (see earlier section). l,2-Dihydro-2-oxoquinoxaline 4-oxide (64) and its N-methyl derivative (65) condense with compoimds containing an active methylene group in the presence of piperidine, yielding 3-alkylated quinoxalinones (66). The oxide 64, when warmed with aqueous potassium cyanide, affords 3-cyano-l,2-dihydro-2-oxoquinoxaline, whereas oxide 65 gives l,2-dihydro-3-hydroxy-2-oxo-l-methylquinoxaline. ... 

Primary aromatic amines can be converted into the corresponding hydroxy compounds in various ways. In some cases this can be done by use of dilute acid or alkali under specific conditions, but that method is used mainly in industry and is rarely suitable for laboratory practice. 4-Amino-2,7- and -2,6-naphthalenedisulfonic acid and 8-amino-1,6-naphthalenedisulfonic acid are converted quantitatively into the corresponding hydroxynaphthalenedisulfonic acids when their acid salts are heated in water at 180° 555 and 2-methoxy-4-nitroaniline affords 4-nitroguaiacol in 86% yield when boiled for 30 hours with aqueous sodium hydroxide.556... 

Formylation of 3-aminophenols leading to intermediates for the synthesis of coumarins and other carbonyl derivatives has been described. Nuclear formylation of 3-dimethylaminophenol with ethyl orthoformate in the presence of 4-nitroaniline by boiling for 5 mins, resulted in formation of 2-hydroxy-4-dimethylaminobenzylidene-4-nitroanHine in 88% yield (ref. 100). 

Oiaminophenol. 4-Hydroxy-w-phenylenediamine [95-86-3] (12) forms leaflets that darken on exposure to ait. It is soluble in acid, alkali, ethanol, and acetone and is sparingly soluble in chloroform, diethji ether, and ligroin. 2,4-IDiaminophenol usually is sold as the sulfate [74283-34 ] (Diamol) or dihydtochlotide salt [137-09-7] (Acrol, Amidol). 2,4-Diaminophenol can be prepared from 2,4-dinitrophenol by catalytic hydrogenation or, less conveniendy, by metal reduction in acid solution (Bfichamp method) (169,170). Alternatively, electrolytic reduction and subsequent hydroxjiation of 1,3-dinitrobenzene or 3-nitroaniLine in sulfuric acid can be undertaken (171,172). 

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