Carbon alkali phenoxide

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. 

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 ... 

For the classical Williamson synthesis an alcohol is initially reacted with sodium or potassium to give an alkoxide, e.g. 1. Alternatively an alkali hydroxide or amide may be used to deprotonate the alcohol. Phenols are more acidic, and can be converted to phenoxides by treatment with an alkali hydroxide or with potassium carbonate in acetone. ... 

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. ... 

Structures of [alkali metal phenoxide C02] complex In the Kolbe-Schmitt reaction, phenyl carbonate (I) was originally proposed as the intermediate[2], but infrared absorption (i.r.) spectra of the intermediate showed a band at 1684 cm which disagrees with I, because an absorption band at 1754 cm of methyl phenyl carbonate is not much different from 1748 cm for dimethyl carbonate.[3] Therefore, the carbonyl of the complex might be in the structures such as (II) - (IV). 

The mechanism of the Kolbe-Schmitt reaction was investigated since the late 1800s, but the mechanism of the carboxylation could not be elucidated for more than 100 years. For a long time, the accepted mechanism was that the carbon dioxide initially forms an alkali metal phenoxide-C02 complex, which is then converted to the aromatic carboxylate at elevated temperature. The detailed mechanistic study conducted by Y. Kosugi et al. revealed that this complex is actually not an intermediate in the reaction, since the carefully prepared phenoxide-C02 complex started to decompose to afford phenoxide above 90 °C. They also demonstrated that the carboxylated products were thermally stable even at around 200 °C. The CO2 electrophile attacks the ring directly to afford the corresponding ortho- or para-substituted products. (When the counterion is large (e.g., cesium) the attack of CO2 at the ortho-position is hindered therefore, the para-substituted product is the major product.)... 

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. 

Organotin alkoxides and phenoxides can be prepared from the reaction of an alkali metal alkoxide or phenoxide with the appropriate organotin halide. Triorganotin alkoxides and phenoxides are available from the reaction of bis(triorganotin) oxides with alcohols or phenols or the corresponding carbonates, and the amides R Sn(NR"2)4 react with alcohols to give the corresponding alkoxides. 

The classical Kolbe-Schmidt reaction treats alkali metal phenoxides and carbon dioxide at higher than atmospheric pressure, giving salicylic acid. Hirao and Kato developed several modifications for industrial production ". Recently, phenol phosphate was enzymatically carboxylated, giving p-hydroxybenzoic acid ". As for related reactions, Sartori and coworkers conducted o-carbamoylation of aluminum or boron phenoxides with alkyl isocyanate ", and Adachi and Sugasawa o-cyanated phenols using methyl thioisocyanate in the presence of BCI3 (equation 54). ... 

Aromatic hydroxycarboxylic acids, especially salicylic acid, have a wide range of applications, for example, as valuable raw materials and intermediates in the production of pharmaceutical chemicals. Originally, salicylic acid was synthesized by the Kolbe-Schmitt reaction [57], which consists of two steps (1) the synthesis and purification of alkali metal phenoxides and (2) carboxylation (Scheme 4.4). Another possible synthetic method is via the attack of a trichloromethyl cation (generated by a copper catalyst from carbon tetrachloride) on the phenoxide anion, followed by hydrolysis of the C—Cl bonds with concentrated sodium hydroxide, because it is fairly difficult to replace an aromatic hydrogen with carboxyl functionality [58]. 

The aryl ether linkage is important in many natural products and pharmaceuticals, including the antibiotic vancomycin [196]. Diaryl ethers have been efficiently prepared by the coupling of fluo-robenzonitriles with a series of phenols in DMSO using potassium carbonate as a base catalyst and with microwave irradiation [197]. A DPT study of the reaction of alkali metal phenoxides with fluo-robenzenes indicated that the role of the metal cation is to aid the binding of the aryl halide and to facilitate fluoride displacement [198]. 

---