M- Nitrophenol

I) When working with larger quantities of material, it is more convenient (and a better yield is obtained) to purify the air-dried product by distillation under diminished pressure. Use the apparatus pictured in Fig. II, 19, 4, and add a few fragments of porous porcelain to the solid. No air inlet can be employed to prevent bumping since this may lead to explosive decomposition. Collect the pure m-nitrophenol at I60-I65°/I2 mm. always allow the flask to cool before admitting air otherwise the residue may decompose with explosive violence. The recovery is over 90 per cent, of the pure m-nitroplienol. 

Phenol may be nitrated with dilute nitric acid to 3deld a mixture of o- and nitrophenols the 3deld of p-nitrophenol is increased if a mixture of sodium nitiute and dilute sulphuric acid is employed. Upon steam distilling the mixture, the ortho isomer passes over in a substantially pure form the para isomer remains in the distillation flask, and can be readily isolated by extraction with hot 2 per cent, hydrochloric acid. The preparation of m-nitrophenol from wt-nitroaniline by means of the diazo reaction is described in Section IV,70. 

A meta nitro group is not directly conjugated to the phenoxide oxygen and thus stabi hzes a phenoxide ion to a smaller extent m Nitrophenol is more acidic than phenol but less acidic than either o or p nitrophenol... 

The titration of a mixture ofp-nitrophenol (pfQ = 7.0) and m-nitrophenol pK = 8.3) can be followed spectrophotometrically. Neither acid absorbs at a wavelength of 545 nm, but their respective conjugate bases do absorb at this wavelength. The m-nitrophenolate ion has a greater absorbance than an equimolar solution of the p-nitrophenolate ion. Sketch the spectrophotometric titration curve for a 50.00-mL mixture consisting of 0.0500 M p-nitrophenol and 0.0500 M m-nitrophenol with 0.100 M NaOH, and compare the curve with the expected potentiometric titration curves. 

By using the same molecular proportions the following m-nitrophenols were prepared in equally good yields from the corresponding m-nitroanilincs 3-methoxy-5-nitrophenol and 3-nitro-4,6-xylenol. In the former case it is advisable to use slightly more ice in the diazotization and add the diazonium solution to a mixture of equal volumes of sulfuric acid and water. 

Dinitrophenol. Yel needles from w or thick crysts from ale mp 144—5° d 1.681 at 20°. Can be prepd by the nitration of m-nitrophenol, with 2,5- and 3,4-Dinitrophenols being formed simultaneously. Very easily sol in eth and hot ale... 

Zeyer J, PC Kearney (1984) Degradation of o-nitrophenol and m-nitrophenol by a Pseudomonas putida. J Agric Food Chem 32 238-242. 

CMHeo030 2 C6H5N03 6 H20 Cyclomaltohexaose -bis(m-nitrophenol), hexahydrate ACDMNP 43 354... 

More recently, Kaiser and coworkers reported enantiomeric specificity in the reaction of cyclohexaamylose with 3-carboxy-2,2,5,5-tetramethyl-pyrrolidin-l-oxy m-nitrophenyl ester (1), a spin label useful for identifying enzyme-substrate interactions (Flohr et al., 1971). In this case, the catalytic mechanism is identical to the scheme derived for the reactions of the cycloamyloses with phenyl acetates. In fact, the covalent intermediate, an acyl-cyclohexaamylose, was isolated. Maximal rate constants for appearance of m-nitrophenol at pH 8.62 (fc2), rate constants for hydrolysis of the covalent intermediate (fc3), and substrate binding constants (Kd) for the two enantiomers are presented in Table VIII. Significantly, specificity appears in the rates of acylation (fc2) rather than in either the strength of binding or the rate of deacylation. 

On various grounds, however, this explanation may be questioned. In particular it may be pointed out that m-nitrophenol behaves like the other two isomers and hence its alkali salts must also be quinonoid in form. But wi-quinones are unknown throughout the whole range of the aromatic compounds. Moreover, there are numerous examples of substances which undergo a deepening in colour when they form salts but cannot change to a tautomeric quinone. Thus the disodium and dipotassium salts of yellowish-brown anthraquinol are deep blood-red in colour (p. 335). 

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