4-Nitro-phenol reaction

The reaction course has not been elucidated (cf. also sodium hydroxide reagent). Hydrolyzation reactions and aromatizations are probably primarily responsible for the formation of colored and fluorescent derivatives. Substituted nitrophenols - e.g. the thiophosphate insecticides — can probably be hydrolyzed to yellow-colored nitro-phenolate anions by sodium hydroxide or possibly react to yield yellow Meisenheimer complexes. Naphthol derivatives with a tendency to form radicals, e.g. 2-naphthyl benzoate, react with hydrolysis to yield violet-colored mesomerically stabilized 1,2-naph-thalenediol radicals. 

Nitrophenyl esters of amino acids, which are important for peptide syntheses, have been obtained in a one-pot reaction from TV-protected amino acids, CDI, and /j-nitro-phenol at room temperature however, better yields of these esters could be achieved by use of TV-trifluoroacetylimidazole. In this reaction a mixed anhydride is presumably formed as an intermediate, which then acylates the alcohol component [17]... 

The existence of a protonated oxazolone has been demonstrated indirectly by a simple experiment. When p-nitrophenol was added to an excess of 2-alkoxy-5(4//)-oxazolone in dichloromethane, a yellow color appeared. The color persisted until all the p-nitrophenol had been consumed by the oxazolone. The anion of p-nitro-phenol is yellow. The explanation for the color of the mixture is the presence of the p-nitrophenoxide anion that was generated by abstraction of the proton by the oxazolone. In summary, protonation of the O-acylisourea suppresses the side reaction of oxazolone formation as well as the side reaction of A-acylurea formation and accelerates its consumption by enhancing its reactivity and generating an additional good nucleophile that consumes it. Protonation of the oxazolone suppresses epimerization by preventing its enolization and also increases the rate at which it is consumed.4 68 78 79... 

N-Carbobenzoxy-L-alanine-/>-nitrophenyl ester is a specific substrate for elastase in which the rate-limiting step is deacylation, that is, hydrolysis of the acyl-enzyme intermediate. In 70% methanol over a reasonable temperature range the energy of activation of the turnover reaction, that is, deacylation, is 15.4 kcal mol. In the pH 6-7 region in this cryoprotective solvent, the turnover reacdon can be made negligibly slow at temperatures of -50 C or below. Under such conditions/i-nitro-phenol is released concurrent to acyl enzyme formation in a 1 1 stoichiometry with active enzyme in the presence of excess substrate. In other words, even at low temperatures, the acylation rate is much faster than deacylation and the acyl enzyme will accumulate on the enzyme. The rate of acyl-enzyme formation can be monitored by following the rate of p-nitrophenol release, and thus the concentration of trapped acyl enzyme may be determined. This calculadon has been carried out and... 

Bruice and Sturtevant, (1959) and Bruice, (1959) found extremely facile intramolecular nucleophilic attack by neighbouring imidazole in the hydrolysis of p-nitrophenyl 7-(4-imidazoyl)butyrate [19]. The rate constant for imidazole participation (release of p-nitro-phenolate) in this reaction is nearly identical with the rate constant for a-chymotrypsin catalysed release of p-nitrophenolate ion [190 min in equation (11) at pH 7 and 25°] from p-nitrophenyl acetate. Comparison of the rate constant for intramolecular imidazole participation to that for the analogous bimolecular reaction (imidazole attack on p-nitrophenyl acetate) (s" /m s )... 

Parathion is also metabolized to diethyl phosphorothioic acid and -nitrophenol in a reaction requiring a cytochrome P-4Jg-containing monooxygenase enzyme system (, 4). Studies with H. 0 have indicated that water in addition to molecular oxygen and NADPH is required in this reaction ( ). Diethyl phosphate and -nitro-phenol can also be formed from parathion in a monooxygenase-catalyzed reaction (6). 

It has seemed desirable to try to detect the postulated acylimidazole intermediate by spectroscopic probing. Acetylimidazole has been shown31 to have an absorbance maximum at 245 nm with an extinction coefficient of 3000. This absorbance should provide a basis for detection of the intermediate. However, in practice the strong absorbances due to the aromatic ester substrate (nitrophenyl caproate) and the product (nitro-phenol(ate)), added to the light scattering from the polymer, have made the spectrophotometric observation of the acylimidazole intermediate unfeasible under the reaction conditions previously described.26... 

Figure 5.1 shows the spectrophoto metrically determined liberation of p-nitro phenol (pNPOH) from pNPOAc in the absence (curve a) and presence (curve b) of metal catalyst. The catalyzed reaction exhibits biphasic kinetics, characterized by an initial burst of pNPOH release, followed by a slower linear phase. 

Accordingly, where possible (for the p-hydroxybenzaldehydes), the aluminium chloride method (Reaction XXVIII.) should be used. The yields are better, the reactions go more smoothly, little resin being formed, while pyrogallols and naphthols, etc., also react. Unfortunately, though the non-formation of other than p-hydroxyaldehydes is often an advantage, it limits the scope of the reaction and necessitates the use of the Reimer method in many cases. It should be noted that the nitro-phenols do not condense with chloroform (B., 9, 423, 824 10, 1562 15, 2685). 

Dihydroxy alcohols and amino alcohols in which the functional groups are not separated by more than four carbon atoms are effective acceptors. There is a general difference in the behavior of these compounds, however, in that hydroxyl alcohols decrease the rate of formation of p-nitro-phenol from p-nitrophenyl phosphate and amino alcohols increase the rate. Amino alcohols are relatively good nucleophiles in reaction with phosphate esters, perhaps because the amino group serves as a general base catalyst (143, 144)-... 

Relative rates of hydrolysis were determined with 0.5 ml reaction mixtures in 0.1 M sodium acetate buffer, pH 5.0, at 37°. Liberated phosphate was measured by the method of C. H. Fiske and Y. SubbaRow [JBC 66, 375 (1925)]. The amounts of enzyme used were 0.22 unit of crystalline enzyme and 0.24 unit of peak II enzyme. The concentration of substrate and inhibitor was 1.0 mM. For inhibitor study, 1.0 mM p-nitrophenyl phosphate was used as substrate. Inhibition was calculated from the amount of p-nitro-phenol released and expressed as fractional inhibition. 

Meng and Sode [35, 36] also reported the preparation of imprinted polymers to be used as reaction vessels for the transesterification of p-nitro-phenol acetate (23) and hexanol. The MIP showed eightfold increased activity when compared to the NIP. 

Thus, p- xylene yielded 2,5-dichloro-p-xylene. The principal reaction with anisole was also chlorination and with phenol nitration when nitration temperature was low (-80°C) both o- and p- nitrophenols were formed. At room temperature chlorination also occurred yielding 2,4-dichloro-6-nitrophenol and 3,6-dichloro-2-nitro-phenol. 

Mono-nitro Phenols.—In the first reaction the product is a mixture of ortho-nitro phenol and para-nitro phenol. The two may be easily separated as the ortho compound is volatile with steam, crystallizing in beautiful yellow crystals, while the para compound is not volatile, being left behind when the mixture is distilled with steam. It is then extracted from the residue by boiling with hydrochloric acid, recrystallized from the same solvent and obtained as fine white needles. The preparation and separation of these two compounds is a very satisfactory laboratory exercise. The meta-nitro phenol can not be pre-... 

Varnali and Hargittai found energies of 30 and 12 kJ/mol for the intramolecular hydrogen bond formation in 2-nitrovinyl alcohol and 2-nitro phenol, respectively [194]. They are far from 57.45 and 50.07 kJ/mol, respectively, obtained according to the classical procedure at B3LYP/6-31G level [189]. To be remembered that the isodesmic reaction technique cannot be used for activation barriers and that different energies will be predicted by different isodesmic reactions. 

Purification and characterizations of extracellular chitinases from the marine bacterium Bacillus sp. LJ-25 were described by Lee et al. (2000a). The purified chitinase so obtained showed a single band on SDS-PAGE and had an MW of approximately 50 kDa. The chitinase was most active and relatively stable at a pH of 7.0. The optimum temperature for this enzyme was around 35 °C when the pH of the reaction was kept at 7.0. The effect of metal ions on chitinase activity showed that Zn2+ strongly inhibited the enzyme activity. However, Ba2+, Co2+, Mn2+, and Cu2+ showed slight inhibition of the enzyme. Substrate specificity studies indicated that colloidal chitin (a substrate of the endo type of chitinase) was efficiently degraded by the chitinase. However, chitin and chitosan were ineffectively hydrolyzed by this enzyme. This chitinase did not hydrolyze /V,iV-diacetylchitobiose, j9-nitro phenol- /V- ace tyl - (3 -1 > - g I u c o s a mine, and Micrococcus lysodeikticus cells, which are known to be the substrates of the exo type of chitinases. 

The former of the two reaction routes is followed preferentially in an acid medium, whereas reaction through the azoxy stage is favored in an alkaline medium nitro-phenols and -anilines, however, are reduced directly under alkaline conditions. All the intermediates of both routes can be isolated on appropriate choice of conditions and, of course, all these intermediates can be reduced to amines, although in this connexion only the azo compounds produced by coupling are important. 

Identification of the Transients. Neutral Solutions. In deaerated 5 X 10"5M p-nitrophenol solution at pH 7, the absorption spectrum with a maximum at 290 n.m. was observed about 20 /xsec. after the end of the radiation pulse (Figure 1-A) when all the hydrated electrons, H and OH radicals have reacted with the p-nitrophenol. The spectra shown in Figure 1-A and 1-B were corrected for the decrease in optical density owing to solute destruction. The G-value for the destruction of p-nitro-phenol was assumed to be equal to the sum of G(e"aq) + G(OH) + G(H) = 6.0 (2, 15, 19). The corrections had a maximum value at 400 n.m. namely, 103% and 130% of the observed optical densities and decreased to 40% and 81% at 290 n.m. for spectrum A and B, respectively. When hydrated electrons are converted to OH radicals by reaction with N20 (II), the absorption at 290 n.m. decreases and the maximum shifts towards 300 n.m. (Figure 1-B). It can be concluded, therefore, that the transient species produced by hydrated electrons as well as OH radicals have an optical absorption in the same wavelength region. 

Yarrowia lipolytica lipase (YLL) activity was performed by continuously measuring the increase in the absoibance in 348 nm produced by the release of p-nitro-phenol in the hydrolysis 0.4 mM p-nitrophenyl-butyrate (pNPB) in 25 mM sodium phosphate buffer pH 7 and 28°C. The reaction was initialized by addition of 0.2 ml of lipase suspension to 2.5 ml of substrate solution. One international unit (lU) of pNPB was defined as the amount of immobilized YLL necessary to hydrolyze 1 pmol ofpNPB per minute in assay conditions [21]. 

The benzene is initially converted to phenylmercuric nitrate which reacts with nitrogen dioxide to yield nitrosobenzene Each of these intermediates has been isolated from the reaction mixture. The nitrosobenzene can react in two wajrs. In nitric acid weaker than 50 per cent, it reacts with 2 moles of nitric oxide to form phenyldiazonium nitrate, a reaction first discovered by Bamberger. The diazonium salt is converted by water to phenol, which is nitrated in steps to the final products. In nitric acid of greater than 50 per cent concentration, the nitrosobenzene is converted directly to p-nitro-phenol without going through the diazonium compound. The p-nitro-phenol is then nitrated further to give the dinitrophenol and picric acid. 

FIGURE 7.11 The kinetics observed in the chymotrypsin reaction. An initial burst of j >-nitro-phenolate is seen, followed by a slower, steady-state release that matches the appearance of the other product, acetate. 

The gas-phase equilibrium between 2-hydroxypyridine and 2-pyridone favours the hydroxy-form, but in the equilibrium between 2-hydroxypyridine iV-oxide and N-hydroxy-2-pyridone, the major tautomer is the hydroxy-pyridone. Bicyclic adducts between 2-pyridones and dimethyl acetylene-dicarboxylate, unobtainable at atmospheric pressure, have been obtained at 10—15 kbar. A novel route to iV-hydroxy-2-pyridone involves the trimethyl-silylation of 2-pyridone followed by oxidation of the resulting 2-(trimethyl-silyloxy)pyridine with the DMF complex of molybdenum pentoxide. p-Nitro-phenols (45) and nitro-acetamides (46) are formed from the reaction of 3,5-dinitro-2-pyridones (43) with the sodium salts of /3-keto-esters (44) (Scheme 20). ... 

After the removal of the AP solution with an aspirator, 5.0 ml of 3.5 mM NPP was added to the AP adsorbed on the glass beads. The reaction was stopped after 3 min by adding 7 ml of a 1 M KH2PO4 solution adjusted with NaOH to pH 8.1. The amount of hydrolyzed p-nitro-phenol was estimated from the absorbance at 402 nm e m ... 

The maximum rates of mineralization of the two compounds decreased with aging (Table 9.11) and it is of interest to note that the phenol was metabohzed at higher rate than the phenanthrene. This could involve differences in the sizes of the inoculum used or differing mineralizing efficiencies of the two strains. The large difference in Kqm between the phenol (64.6) and phenanthrene (6310) calculated from log iifow values of 2.04 and 4.46 (see Sorption, Chapter 3) would result in a large difference in Ce for equivalent levels of xjm. The proportion of the 4-nitro-phenol (piifa 7.08) in solution would be enhanced by the fact that mineralization reaction were carried out around pH 7. 

---