Carbon dioxide with phenoxides

Kolbe hydrocarbon synthesis orgchem The production of an alkane by the electrolysis of a water-soluble salt of a carboxylic acid. kol-bo. hT-dro kar-bon, sin-th3-s3s Kolbe-Schmitt synthesis org chem The reaction of carbon dioxide with sodium phenoxide at 125°C to give salicyclic acid. kol-bo shmit, sin-th3-s3s Konowaioff ruie phys chem An empirical rule which states that in the vapor over a liquid mixture there is a higher proportion of that component which, when added to the liquid, raises its vapor pressure, than of other components., k6-n9 va-lof, rul ... 

The manufacture of aspirin is based on the synthesis of salicylic acid from phenol. Reaction of carbon dioxide with sodium phenoxide is an electrophilic aromatic substitution on the ortho, para-directing phenoxy ring. The ortho isomer is steam distilled away from the para isomer. 

Hydroxybenzoic acid has been prepared by heating potassium phenoxide in a stream of carbon dioxide or with carbon tetrachloride, and by heating jfr-cresol with alkalies and various metallic oxides. The procedure described above is similar to one which appears in the early literature ... 

In order to rationalize the orr/zo-selectivity observed in the reaction of sodium phenoxide 1 with carbon dioxide, the formation of a complex 3 is assumed. By that complexation the carbon dioxide becomes polarized, and its electrophilic character is increased. Complex 3 is of suitable geometry for reaction with the activated ort/zo-carbon center " ... 

The para-substituted product, which is not accessible from complex 3, can however be obtained from reaction of potassium phenoxide with carbon dioxide. 

Sodium 4-methylphenoxide solution was dehydrated azeotropically with chlorobenzene, and the filtered solid was dried in an oven, where it soon ignited and glowed locally. This continued for 30 min after it was removed from the oven. A substituted potassium phenoxide, prepared differently, also ignited on heating. Finely divided and moist alkali phenoxides may be prone to vigorous oxidation (or perhaps reaction with carbon dioxide) when heated in air. 

Still another possibility in the base-catalyzed reactions of carbonyl compounds is alkylation or similar reaction at the oxygen atom. This is the predominant reaction of phenoxide ion, of course, but for enolates with less resonance stabilization it is exceptional and requires special conditions. Even phenolates react at carbon when the reagent is carbon dioxide, but this may be due merely to the instability of the alternative carbonic half ester. The association of enolate ions with a proton is evidently not very different from the association with metallic cations. Although the equilibrium mixture is about 92 % ketone, the sodium derivative of acetoacetic ester reacts with acetic acid in cold petroleum ether to give the enol. The Perkin ring closure reaction, which depends on C-alkylation, gives the alternative O-alkylation only when it is applied to the synthesis of a four membered ring ... 

Since, in Kolbe s synthesis, as here described, the mono-sodium salicylate reacts to some extent with unchanged sodium phenoxide, producing the di-sodium salt, part of the phenol is liberated and excluded from the reaction. The reaction proceeds to completion if the sodium phenoxide is heated to about 150° for a long time, with carbon dioxide under pressure in the autoclave. This is the technical method of Schmitt. 

Carboxylation of sodium phenoxides with carbon dioxide, to give salicylic acid, the precursor to the synthesis of aspirin. 

Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic substitution with carbon dioxide, a weak electrophile. Ortho hydroj benzoic acid is formed as the main reaction product. 

Recent work shows that a phenoxide-C02 complex is formed competitively with direct carboxylation. This does not go on to form products, but rather decomposes to phenoxide and carbon dioxide. (Y. Kosugi, Y. Imaoka, F. Gotoh, M. A. Rahim, Y. Matsui, K. Sakanishi, Organic and Biomolecular Chemistry 2003,1, 817)... 

The reaction of iV-(2,4-dinitrophenyl)amino acids with base in aqueous dioxane has been shown to give benzimidazole iV-oxides (7). The rate-determining step is likely to be formation of an iV-alkylidene-2-nitrosoaniline intermediate (6), which is followed by rapid cyclization and decarboxylation.19 The loss of carbon dioxide from perbenzoate anions has been investigated by mass spectrometry and electronic structure calculations. The results, including isotopic labelling experiments, support a mechanism involving initial intramolecular nucleophilic attack at either the ortho- or ipso-ring positions. They also indicate that epoxides may be intermediates en route to the phenoxide products.20 There has also been a theoretical study of the formation of trichlorinated dibenzo-/ -dioxins by reaction of 2,4,5-trichlorophenolate ions with 2,4-dichlorophenol.21... 

The reaction of a phenoxide ion with carbon dioxide to produce a car-boxylate salt is called the Kolbe reaction. 

Phenoxide ions are so strongly activated that they undergo electrophilic aromatic substitution with carbon dioxide, a weak electrophile. The carboxylation of phenoxide ion is an industrial synthesis of salicylic acid, which is then converted to aspirin, as shown on p. 802. 

The phenoxide ion is even more reactive towards electrophilic attack than phenol. It will even react with such weak electrophiles as carbon dioxide. This reaction, known as the Kolbe-Schmitt process, is used industrially to prepare salicylic acid, a precursor in making aspirin. 

The formation of the phenoxide anion enhances the reactivity of the ortho and para positions of the aromatic ring towards electrophilic reagents. The reaction of the phenoxide anion with carbon dioxide at 130 °C leads to ortho carboxylation (the Kolbe reactior. Thus phenol gives salicylic acid (4.4), the acetate of which is aspirin. The reaction is reversible and ortho phenolic acids undergo decarboxylation on heating. 

The nmr chemical shifts of alkah metal ( K, Na etc.) phenoxide moved to down field upon formation of the complex, [ phenoxide-M CO2] with carbon dioxide in the Kolbe-Schmitt reaction. The complex formed under pressure of carbon dioxide showed more increments in weights and chemical shifts, as much as 0.72 ppm of (5 paia of potassium phenoxide at 5 MPa. The kinetic studies on the carboxylation of resorcinol in aqueous hydrogencarbonates with carbon dioxide revealed an equilibrium between resorcinol and the product or resorcylic acid. 

The powdered alkali metal (K, Na etc.) phenoxide (ca.O.lg) was placed in a vial fLUed with carbon dioxide, and covered with parafihn. Carbon dioxide of purity more than 99.95% was supplied through a capillary tubing at room temperature. After the absorption of the gas, the weight increment was measured, and a portion of the sample was transferred in an nmr tube of 5 mm and dissolved in DMF with acetone-de, or in DMSO-d with addition of TMS. The nmr spectra on a JEOL-JNM GX 270 spectrometer were taken without delay. For the kinetic studies, a 150 mL aqueous solution containing resorcinol and potassium hydrogencarbonate was kept at 80 C with or without bubbling carbon dioxide, then an ahquot was taken at given time for nmr and/or HPLC analyses. ... 

In the present studies, nmr spectroscopy was used and the existence of the complex has been clearly proved. Carbon dioxide is exothermically absorbed by dried potassium phenoxide, of which weights increase. Upon dissolving in nmr solvents, such as DMF and DMSO-de, a part of the complex decomposes with liberation of carbon dioxide gas. In spite of the loss of portions of the complex, nmr... 

Kosugi, Y., Takahashi, K., Imaoka, Y. Solvent-assisted carboxylation of alkali metal phenoxide with carbon dioxide. J. Chem. Res., Synop. 1999, 114-115. 

Kosugi, Y., Imaoka, Y., Gotoh, F., Rahim Mohammad, A., Matsui, Y., Sakanishi, K. Carboxylations of alkali metal phenoxides with carbon dioxide. Org. Biomol. Chem. 2003, 1,817-821. 

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