2-nitro-phenoxides

Kinetic studies on 2-, 3-, and 4-chloro-l-methylpyridinium salts showed a 30 10 ratio of the reaction rates at 50° with 4-nitro-phenoxide ion in methanol. The activation energy for reaction at the 4-position is one kilocalorie lower ( 8-fold higher rate) than for reaction at the 2-position. The reversal in rates relative to the corresponding halopyridines is the result of a much higher entropy of activation for the 2-chloro compound. The 3-chloro compound has a favorable entropy of activation also, but the energy of activation is about 13 kcal higher than that of the isomers (cf. Table II and Section III, A, 2). 

Figures I and II show a comparison of the reaction profile for PPY and polymer catalyzed hydrolysis for p-nitrophenylacetate and p-nitrophenylcaproate monitored by the appearance of p-nitro-phenoxide absorption by UV-VIS spectroscopy. These results confirm the effectiveness of the interactions between the hydro-phobic polymer chain and the hydrocarbon portion of the substrate, as it was previously mentioned, in accordance with the observations of Overberger et al (20).

Nucleophilicity of the guanidine must be. carefully controlled to avoid arylation of the catalyst itself. This could be easily accomplished through a proper choice of the substituents. Note also that delocalization of charge over the three nitrogens in the assumed intermediate guanidinium cation enhances the nucleophilicity of its counter anion, e.g. the p.nitro phenoxide anion. 

For diastereoisomeric 2-chloro-4-isopropyl-5,5-dimethyl-1,3,2x -dioxaphosphorinanes, the displacement of chlorine by aryloxide anions proceeds readily complete inversion was observed with the weakest nucleophile examined,viz., 4-nitro-phenoxide, a feature already recorded for less substituted 1,3,2-dioxaphosphorinanes, and a comparison of the inversion, or retention (as observed with other nucleophiles) ratios with those for other cyclic phosphorus(V) chlorides in the same series suggests that the 4-isopropyl group exerts an appreciable steric control on the stereochemistry of the displacement process. 

While several optically active oxazolones have been prepared, these intermediates are likely to undergo racemization in peptide syn-thesis.67 68 Thus, 2-phenyl-L-4-benzyl-2-oxazolin-5-one (26) was synthesized, and its rate of racemization with nucleophiles such as p-nitro-phenoxide ion and phenylalanine methyl ester was studied. The rates of... 

AI3-09021 Atonik EINECS 212-536-4 EPA Pesticide Chemical Code 129077 HSDB 2592 Phenol, 4-nitro-, sodium salt Phenol, p-nitro-, sodium salt PNSP Sodium 4-nitrophenolate Sodium 4-nitrophenoxide Sodium nitrophenate Sodium p-nitrophenate Sodium p-nitro-phenol Sodium p-nitrophenolate Sodium p-nitro-phenoxide. Plant growth regulator. Registered by EPA as a plant growth regulator. Asahi Chem. Industry. 

In the second major method of peptide synthesis the carboxyl group is activated by converting it to an active ester, usually a p-nitrophenyl ester. Recall from Section 20.11 that esters react with ammonia and amines to give amides. p-Nitrophenyl esters are much more reactive than methyl and ethyl esters in these reactions because p-nitro-phenoxide is a better (less basic) leaving group than methoxide and ethoxide. Simply allowing the active ester and a C-protected amino acid to stand in a suitable solvent is sufficient to bring about peptide bond formation by nucleophilic acyl substitution. 

Many AMY reference methods based on malto-oligosaccharides with auxiliary enzymes and/or indicator enzymes have been recommended. For the direct method, an artificial substrate, 2-chloro-4-nitrophenyl-a-D-maltotrioside (CNPT), is used for continuous monitoring of AMY activity. AMY hydrolyzes CNPT to maltotriose and 2-chloro-4-nitrophenol at high thiocyanate concentrations. The reaction is followed by monitoring the increase in absorbance due to the production of 2-chloro-4-nitro-phenoxide at 405 nm. A side reaction (reaction [X]) occurs with formation of glucose and 2-chloro-4-nitrophenyl-a-D-maltose, which accovmts for 8% of the product formed. 

Fig. 2. Br/zinsted plot for the cyclization of 4-chlorobutanol in water at 25°C. Data points (left to right) correspond to water, 2,4-dinitrophenoxide, 2,4,6-trichlorophenoxide, 4-nitro-phenoxide, phenoxide, 2,2,2-trifluoroethoxide, and hydroxide.

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... 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Aromatic haUdes do not react easily with phenoxide ions to produce diaryl ethers unless the aromatic haUde is substituted with one or more electron-withdrawing groups, eg, nitro or carboxyl groups. The Ullmann reaction uses finely divided copper or copper salts to cataly2e the reaction of phenoxides with aromatic haUdes to give diaryl ethers. 

Nitrodiphenyl ether has been prepared by heating p-nitro-chlorobenzene with potassium phenoxide and phenoD and by the nitration of diphenyl ether. ... 

Mononitration of a mixture of J- and 4 chlorobenzotnfluondes followed by nucleophilic substitution by hydroxide, ammonia, or a primary or secondary amine in dimethylformamide, leads to 5 chloro 2 nitrobenzotrifluoride The 4-chloro-3-nitro isomer selectively reacts and can be removed as a water-soluble phenoxide [19] (equation 16)... 

Phenol has different chemical properties from those of typical alcohols. Display the electrostatic potential map for phenol. Does this suggest that phenol is likely to be a stronger or weaker acid than any of the compounds discussed above Compare the electrostatic potential map for 4-nitrophenol to that for phenol. What effect does substitution by nitro have on acid strength Explain your result by considering charge delocalization in the conjugate base. Draw all reasonable Lewis structures for phenoxide anion and for 4-nitrophenoxide anion. Which is more delocalized Is this consistent with experimental pKa s ... 

The reaction rates for phenoxide ions are thus similar to those observed for dialkylanilines (and also enolate ions) and seem to represent an upper limit for brominating rate in aqueous solution. Consequently, the reactions have an almost zero activation energy and there is an apparent lack of deactivation by the nitro group. That bromination by BrJ occurs in this reaction is not surprising, since the high reactivity of the phenoxide ion means that it will not discriminate very much between electrophiles of differing reactivity. 

Solvent-free SNAr reactions under solid-liquid PTC conditions were realized by using methoxide or phenoxide as nucleophiles. The main results, and comparison with those from classical heating, are indicated in Tab. 5.24 for activated (e.g. 4-nitro-halobenzenes) or nonactivated (e.g. a-naphthyl halides) substrates [74]. 

The reaction was carried out with /3-keto esters, /3-diketones, malonate, a-formyl ketones, a-cyano and a-nitro esters, cyanoacetamide, and phen-ylsulfonylacetate. (PPh3)2PdCl2 was used with sodium phenoxide. Also, Pd(OAc)2 and PPh3 are good catalysts. When bidentate ligand was used, the 1 1 rather than 1 2 addition reaction took place (56). For example, bis(diphenylphosphino) 1,2-ethane (39) produced a mixture of the following 1,4- (59) and 1,2- (60) addition products ... 

Let us take the case of phenols and nitro-phenols. The phenoxide ion C6 H50 is colourless, but p nitro phenol is yellow, because the -N02 group in /(-position produces a yellow ion—p.N02-C6H40 . Similarly triphenylmethyl cation is colourless or pale yellow or pale yellow in acidic solution, but the corresponding ion containing two or three OH groups in para position produces deep red colour. 

Reaction of potassium phenoxide with p-nitro-bromobenzene in the presence of 18-crown-6 [3] anddibenzo-18-crown-6 111] at 100°C ... 

Alkoxide or aryloxide anions are also reputed to be inactive in Sr I reactions. There is, however, one example of such a reaction at an sp carbon the nitro-derivative of 4-nitrocumyl reacts with phenoxide and 1-methyl-2-naphthoxide ions yielding the corresponding ethers (Kornblum et al., 1967). A similar reaction has been reported for halobenzenes in t-butyl alcohol upon stimulation by sodium amalgam (Rajan and Sridaran, 1977). This reaction could not, however, be reproduced (Rossi and Pierini, 1980) and other attempts to make phenoxide ions react at sp carbons have been equally unsuccessful (Ciminale et al, 1978 Rossi and Bunnett, 1973 Semmelhack and Bargar, 1980). It has been found, more recently, that phenoxide ions react with a series of aryl halides under electrochemical induction, but that the coupling occurs at the p- or o-phenolic carbon rather than at the phenolic oxygen (Alam et al, 1988 Amatore et al, 1988). This is... 

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