P-Nitrophenol, formation

Cellobiase can be measured by following the glucose production from cellobiose and cellodextrins, the saligenin from salicin, and the p-nitrophenol formation from its / -glucoside (2). 

In model (laboratory) experiments, the half-life of MCPA was about 3 days, suggesting that particles might have to be airborne for appreciable time periods in order for breakdown to occur. However, atmospheric drift of emulsified parathion (0 0-diethyl G-p-nitrophenyl phosphorothionate) underwent substantial photooxidation, isomerization, and p-nitrophenol formation within a few minutes (Figure 4) (14). 

The nitrosophenol (10), which may be isolated, is oxidised very rapidly by nitric acid to yield the p-nitrophenol (11) and nitrous acid more nitrous acid is produced thereby and the process is progressively speeded up. No nitrous acid need be present initially in the nitric acid for a little of the latter attacks phenol oxidatively to yield HN02. The rate-determining step is again believed to be the formation of the intermediate (9). Some direct nitration of such reactive aromatic compounds by N02 also takes place simultaneously, the relative amount by the two routes depending on the conditions. 

When p-nitrophenolate is incrementally added to a-cyclodextrin in water, the ultraviolet spectrum of this anion changes such that successive spectra give rise to two isobestic points (Figure 5.2). Such behaviour is in accord with the formation of a 1 1 species. The spectral changes may be used for the direct calculation of K, which in this case was found to be approximately 104 dm3 mol-1 (Cramer, Saenger Spatz, 1967). 

Figure 5.2. Spectral changes on incremental addition of p-nitrophenolate to a-cyclodextrin illustrating complex formation (from Cramer, Saenger Spatz, 1967).

Biaryl ethers are a well-known motif in medicinal chemistry. The reaction of p-nitrophenol with 2,4-dichloropyrimidine was performed in a mixture of acetone and water from which the product precipitated after completion. Work-up and isolation of the product was therefore very simple. We also observed the formation of a by-product (depend-... 

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... 

Section 6.2, the crystal forces are of magnitude comparable to those inducing complex formation. Thus a complex in the solid state can have a different structure from that in solution. The complex of p-nitrophenol 74 with hexakis(2,6-di-OMe)-a-cyclodextrin 75 illustrates this point, exhibiting strikingly different modes of entrance of the guest into the host cavity in these two states (Figure 3.4) [39]. Nevertheless, numerous solid state studies ofthe complexes... 

Tetranuclear aromatic diamines were prepared on the basis of bis-phenols derived from 1,1,1-trichloro-2,2-di-(p-methoxyphenyl)-ethane under the action of pyridine hydrochloride [26, 27]. Interaction of the bis-phenols with two-fold molar amounts of p-nitrochlorobenzene led to the formation of 4,4 -bis(/ -nitrophenoxy [-arylenes, which were reduced to the corresponding 4,4 -bis(/ -aminophenoxy[-arylenes [28] (Scheme 2.11). Similar compounds containing two additional amino groups were prepared by the interaction of 3,3 -dinitro-4,4 -dichlorobenzophenone with two-fold molar amounts of potassium p-nitrophenolate [29] followed by reduction of the tetranitro compounds thus formed [29] (Scheme 2.12). 

The acylenzyme E—O—COOEt is rapidly formed but hydrolyzes slowly. Note that about 0.63 mol of p-nitrophenol is released per mole of enzyme in the burst. Either the enzyme is only 63% pure (active), or the rate constant formation of the acylenzyme is not sufficiently greater than that for deacylation for the acylenzyme to accumulate fully. [From B. S. Hartley and B. A. Kilby, Biochem. J. 56, 288 (1954).]... 

In contrast to the simple alkoxy radicals, the 0-0 radical is seemingly quite stable against further oxidation by 02. In addition, the odd electron in the 0-O is delocalized by resonance, and can facilitate o- and p-addition of N02 to the benzene ring. The phenolic H—O bond of p-nitrophenol must be formed intermolecularly, whereas an intramolecular H-atom transfer cannot be ruled out for the formation of o-nitrophenol. The detailed mechanism for these final steps is presently unknown. 

The increase in rate of formation of p-nitrophenol from p-nitrophenyl phosphate as a substrate, in the presence of an acceptor, tris, is explained by the scheme which shows that the enzyme form produced by transphosphorylation is the active Ep. The slow conversion of Ett to Ep is thus... 

The initial evidence for the formation of an acyl-enzyme ester intermediate came from studies of the kinetics with which chymotrypsin hydrolyzed analogs of its normal polypeptide substrates. The enzyme turned out to hydrolyze esters as well as peptides and simpler amides. Of particular interest was the reaction with the ester p-nitrophenyl acetate. This substrate is well suited for kinetic studies because one of the products of its hydrolysis, p-nitrophenol, has a yellow color in aqueous solution, whereas p-nitrophenyl acetate itself is colorless. The change in the absorption spectrum makes it easy to follow the progress of the reaction. When rapid-mixing techniques are used to add the substrate to the enzyme, an initial burst of p-nitrophenol is detected within the first few seconds, before the reaction settles down to a constant rate (fig. 8.8). The amount of p-nitrophe-... 

DTA showed that o-nitrophenol and sodium hydroxide gave a sharp exotherm at 46°, and p-nitrophenol at 95°, while m-nitrophenol gave no significant evidence of reaction below 200°C. o-Nitroaniline gave a sharp exotherm at 217°, and p-nitroaniline at 246°C [5]. Electronic excitation of TNT leads to formation of <7-quinonoid transient intermediates, and action of various bases leads to deflagration of molten TNT [6]. 

The SnAR mechanism is an addition-elimination mechanism that proceeds through a carbanion with delocalized electrons (a Meisenheimer complex). The following steps show the mechanism for the formation of p-nitrophenol from p-nitroiodobenzene. 

In order to reach a conclusion when and how and, and to some extent, how much of a particular insecticide was administered, the form and quantity in which the insecticide exists in different tissues and in blood and urine may give valuable clues. Indeed, an intelligent deduction is also based on the knowledge of metabolic pathways and formation of other derivatives. Thus, as parathion is excreted in the urine ultimately as p-nitro-phenol, urinary p-nitrophenol levels may indicate the extent of exposure to parathion ). In cases of mild and moderate exposure, the excreted p-nitrophenol in urine was found to be of the order of 0.057 to 0.322 mg. percent. In severe and fatal cases of poisoning by parathion, the level of p-nitrophenol in urine was from 0.16 to 1.16 mg. percent. para-Nitrophenol thus is rapidly excreted in urine and no longer detected 48 hours after the exposure to the pesticide. 

To help characterize the interactions of some drugs and metabolites with HSA and their competition for its limited number of binding sites, we and others have studied the influence of those substrates on its acetylation by p-nitrophenyl acetate (29,30,31,32,33). This reaction is very fast and results in the irreversible acetylation of a particular tyrosine residue (i.e. 411) which is located in a major apolar binding site of that protein (34). Because this reaction is so fast under most conditions, competing reactions are not significant and formation of p-nitrophenolate is a convenient reflection of the reaction rate (35). 

Finally Hubner and W. Schneider [21] defined the conditions under which the formation of the two isomeric dinitrophenols must proceed and pointed out the difference in their structures. They proved the p- nitrophenol was nitrated to 2,4-dinitrophenol when using 54% nitric acid, o- Nitrophenol is slightly more difficult to nitrate and yields a mixture of 2,6- and 2,4-dinitrophenols. The two isomers may be separated by steam distillation, since the 2,4- is more volatile than the... 

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