Phenol, o-Nitro

Other Names Phenol, o-nitro- 2-Hydroxynitrobenzene 2-Nitrophenol NSC 1552 o-Hydroxyni-trobenzene o-Nitrophenol CA Index Name Phenol, 2-nilro-CAS Registry Number 88-75-5 Merck Index Number 6620 Chemical Structure... 

Phenol, 2,A,6-Triphenyl-phenol, o-Nitro phenol. Resorcinol, Pyrogallol Picric acid Aminoacids Buffer pH M-4-.8 HCOOH, CHsCOOH, C2H C00H, Pivalic acid, CsHeCOOH Tartaric acid Salicylic acid H2NCH2COOH, Histidine, -Alanine... 

If phenol is treated even with dilute nitric acid at room temperature, nitration readily occurs with the simultaneous formation of the yellow o-nitro-phenol and the white /> nitrophenol. These compounds can be readily... 

Coloured salts loith alkalis. Dissolve a few crystals of o-nitro-phenol in a few ml. of 10% NaOH solution. An orange-coloured solution is produced, and becomes almost colourless on the addition of acids. Alkali restores the orange coloration, and so the solution exhibits the properties of an indicator. 

We might have thought that the o-nitro group would provide stabilization for the hydrox-ylamine and the phenol by two mechanisms (a) enhanced (i.e. zwitterionic, dipolar, quinonoid-like) resonance as is often discussed for o- and p-nitroaniline, cf. Reference 12, and (b) intermolecular H—O hydrogen bonding between the nitro and hydroxyl groups. 

Fig. 2. The anion [PhCOCHNOHOCgH NOa]- in potassium hydrogen (o-nitro-phenolate, isonitrosoaceto-phenonate) (0), showing its contacts to one K+ ion...

Problem 19,14 Assign numbers from 1 for least to 4 for most to indicate the relative acid strengths in the following groups (a) phenol, m-chlorophenol, m-nitrophenol, m-cresol (b) phenol, benzoic acid, p-nitro-phenol, carbonic acid (c) phenol, p-chlorophenol, p-nitrophenol, p-cresol (d) phenol, o-nitrophenol, m-nitrophenol, p-nitrophenol (e) phenol, p-chlorophenol, 2,4,6-trichlorophenol, 2,4-dichlorophenol (/) phenol, benzyl alcohol, benzenesulfonic acid, benzoic acid. ... 

The impurities present in aromatic nitro compounds depend on the aromatic portion of the molecule. Thus, benzene, phenols or anilines are probable impurities in nitrobenzene, nitrophenols and nitroanilines, respectively. Purification should be carried out accordingly. Isomeric compounds are likely to remain as impurities after the preliminary purifications to remove basic and acidic contaminants. For example, o-nitrophenol may be found in samples of p-nitrophenol. Usually, the o-nitro compounds are more steam volatile than the p-nitro isomers, and can be separated in this way. Polynitro impurities in mononitro compounds can be readily removed because of their relatively lower solubilities in solvents. With acidic or basic nitro compounds which cannot be separated in the above manner, advantage may be taken of their differences in pKg values. The compounds can thus be purified by preliminary extractions with several sets of aqueous buffers of known pH (see for example Table 19, p. 43) from a solution of the substance in a suitable solvent such as ethyl ether. This method is more satisfactory and less laborious the larger the difference between the pK value of the impurity and the desired compound. Heterocyclic nitro compounds require similar treatment to the nitroanilines. Neutral nitro compounds can be steam distilled. 

CST sometimes gives some insight into molecular structure. Thus o-nitro-phenol has a CST with hydrocarbons much lower and with water much higher than do m-nitrophenol and p-nitrophenol. This indicates some hydrogen bonding in the ortho isomer, so that it resembles an ester in its solubility relationships. 

Compounds from o-Nitro-p-cresol and 2 6-Dinitrophenol.—These phenols yield respectively (C6H5)4Cr.0.C6H3(N02)CH3, red needles, M.pt. 135° C. with explosion, and (C6H5)4Cr.0.C6H3(N02)2, orange-red plates, melting and violently exploding at 160° C. 

The whole is heated to 70°C and stirred for 2 hr at 70-80°C. Nitration is complete if a sample of the product has a melting point of 47.6°C, and, when steam distilled after being brought to alkalinity, the distillate does not smell of o- nitro-phenol. After nitration has been completed, the whole is cooled to 50°C diluted at this temperature with 390 kg of water and allowed to remain at rest for separation. The lower spent acid layer, containing 78% of H2S04 is used for mononitration. 

The synthetic route is based on the preparation of the M(4-6) and the M(2-4) subunit by intramolecular Sf.jAr cyclizations of suitable precursor peptides with ort/ o-nitro-substituted haloarene residues and a central phenolic unit (Schemes 2 and 4). This concept was originally developed by Zhu and co-workers and applied successfully to the synthesis of cyclic peptides of the vancomycin family, e. g. to the synthesis of K-13 [13]. 

A convenient and inexpensive method to transfoim election rich aromatic aldehydes to phenols, or a,3-unsaturated aldehydes to vinyl formates, utilizes 30% hydrogen peroxide cat yzed by bis(o-nitro-phenyl) diselenide. A two-step formylation/MCPBA oxidation procedure (Scheme 25) was utilized by Kishi and coworkers in the 100 g scale conversion of 2,6-dimethoxytoluene to the mitomycin precursor (76). An organic peroxy acid was not required for the conversion of 9-formyl-6-methylellipticine (77) to 9-hydroxyellipticine (78 Scheme 26). Under these conditions, the pyridine nitrogen was not oxidized. 

If the monosodium salt of 3-nitro-4-hydroxyphenylarsinic acid is used instead of the trisodium salt, reduction with sodium bisulphite at room temperature gives mainly 8-nitro-4-hydroxyphenylarsenoxide, whilst in boiling aqueous solution the arsenic is eliminated and o-nitro-phenol obtained. ... 

Mercuration of p-Hydroxy-m-nitrophenyl carbinol.— The carbinol is prepared by the action of bromomethyl alcohol on o-nitro-phenol and then treated with 2 mols. of mercuric acetate in alcohol-acetic acid solution. Fine, pale yellow needles separate, which may be recrystallised from 20 per cent, acetic acid (I,). This compound does not form an inner anhydride as in the preceding ease, although the mercury is in the ortho position to the hydroxyl group. The latter fact w as established by treating the compound with a solution of iodine in potassium iodide, when 3-iodo-4-hydroxy-5-nitrobenzyl alcohol is obtained. Treatment with acetic anhydride yields a monoacetyl derivative (II.) ... 

T. Urbanski, Witanowski and associates [42] found convincing proof of the hydrogen bond between the phenolic group and the o-nitro group through H-NMR examination of dilute solutions of nitrophenols, 2,4-dinitrophenol and picric acid. Thus o-nitrophenol gives 5 = 10.67 ppm whereas m- and p-nitro-phenols 4,87 and 5.14 ppm respectively. 

T. Urbanski and D browska [33a] examined infra-red spectra of mono-, di-, and trinitrophenols and particularly [33b] the action of solvents on hydrogen bonding between o-nitro and the phenolic group. They found that polar solvents can break a hydrogen bond. This is discussed in the paragraphs on hydrogen bonds and in the description of dinitro and trinitro phenols. 

The mechanism of the substitution of sulphonic groups in phenol by nitro groups was extensively studied by Lesniak and T. Urbartski [130 and to this purpose the chromato-polarographic method introduced by Kemula and associates 11311 was used. The trend of the nitration of o and p-phenolsulphonic acids with nitric acid can be depicted by diagram (16a) ... 

It should be noted that one is not restricted to log D and pKa combinations. By using log D and a parameters for example, the a-term will represent only the electronic component related to mechanism. On the subject of sigma values, care should be taken to use ortho values for o-substituents [see Norrington et a (14)] when acidity is a property of interest. Both StockdaTF and Selwyn (13 ) and Motais et al (15) for the phenols of Table V used, for example, 0.23 instead of 0.68 for o-chloro 0.80 instead of 1.24 for o-nitro. 

On nitrating the homologues of phenol, the nitro-groups always enter the o- and p-positions to the hydroxyl group, and never the m-position. In order to prepare m-nitrophenol, it is necessary to start from m-nitro-aniline this is diazotised and its diazo-solution boiled with water. 

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