Phenoxides, reactions with nitro

Phenoxides react with nitro, fluoro-, or chloro-substituted phthalic anhydrides (96) to give substituted phthalic anhydrides (97). The success of the reaction is dependent on the conditions and the leaving group, and, despite the formation of by-products, can lead to product yields of up to 87% when the leaving group is F. 

A kinetic study of the deprotonation-reprotonation behaviour of (4-nitrophenyl)-nitromcthane in 50% H2O-50% Me2SO mixtures promoted by bases (phenoxide and carboxylate ions, primary amines) has revealed a one-step equilibration at pH > 4.2 the equilibration in acidic media is complicated by protonation of the exocyclic nitro group.142 The results suggest that the substrate acts essentially as a nitroalkane rather than a /j-nitrotolucnc. A further study of kinetics of deprotonation of (4-nitrophenyl)nitromethane has provided evidence of a steric effect on proton tunnelling on reaction with /V -propyl-A./V-dipropylbcnziinidamidc.143... 

Separation of the p-nitro-substituted aryl halide and reaction with phenoxide ion complete the synthesis. 

The reaction of phenols with nitrous acid gives the ortho- and para-nitroso products, which are formed through a neutral dienone intermediate, the proton loss from the latter being the rate-limiting step" " . It has been shown that the nitrous acid can act as a catalyst for the formation of the nitro derivatives. Thus the conventional preparation of nitro compounds by the oxidation of nitroso compounds may be replaced by methods using an electron-transfer pathway in certain cases. In the latter method, the phenoxide reacts with nitrosonium ion to give the phenoxy radical and nitric oxide radical. The nitric oxide radical is in equilibrium with the nitronium radical by reaction with nitronium ion. The reaction of the phenoxy radical with the nitroninm radical resnlts in the formation of the ortho- and para-mixo prodncts" . Leis and coworkers carried ont kinetic stndies on the reaction of phenolate ions with alkyl nitrites and fonnd that the initially formed product is the 0-nitrite ester, which evolves by a complex mechanism to give the ortho-and the para-nitro products". ... 

Williams, R, and Donahue, P, Reactions of Phenoxides with Nitro- and Halo Substituted Phthalimides, J. Org. Chem., 42(21) 3114-3419,1977. Williams, R, Relies, H., ManeUo, J., and Donahue, P, Reactions of Phenoxides with Nitro-Substituted Phthalate Esters, J. Org. Chem., 42(21) 3419-3425, 1977. 

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. 

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).

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 ... 

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

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