There are many studies on the reaction and chemical property of carbon dioxide, and carbon dioxide is practically used in various fields. In this paper, the carboxylation of alkali phenoxides with carbon dioxide is reviewed and the chemical behavior of carbon dioxide in the reaction is discussed from the viewpoint of the use of carbon dioxide in industrial organic chemistry. The production of hydroxybenzoic acids from alkali phenoxides and carbon dioxide is one of some examples in which carbon dioxide is used as raw materials in industrial organic chemistry. A large portion of salicylic acid and
p-hydroxybenzoic acid prepared by the process have been used for preparation of pharmaceuticals. Recently, bifunctional
p-hydroxybenzoic acid was polymerized and the characteristic properties of the polymer have stimulated investigation of polymerization using
p-hydroxybenzoic acid. The carboxylation of alkali phenoxides with carbon dioxide is carried out in a heterogeneous system which consists of the solid phenoxide and carbon dioxide under a pressure. The mechanism of the carboxylation of sodium and potassium phenoxides in the heterogeneous system and the chemical behavior of carbon dioxide in the system are reviewed. The improvements of the procedure and method of the carboxylation are also described.
Since the remarkable solubility of alkali phenoxides in polar and aprotic solvents such as DMF, DMSO and HMPA was found, it has become feasible to undergo the carboxylation at a homogeneous system. The carboxylation of alkali phenoxides with carbon dioxide in the solutions undergoes at mild conditions. Furthermore, it is noteworthy that the predominant carboxylation at
p-position of the phenoxide is observed even in the case that sodium phenoxide is used. The reaction of carbon dioxide and the alkali phenoxides in DMF is discussed in connection with an activation of carbon dioxide, and it is suggested that the remarkable feature of the carboxylation in the solution may be caused by the solvation of the alkali phenoxides with the solvent and the activation of carbon dioxide by the solvated alkali phenoxides. Alkali alkylcarbonates are regarded as reagents fixing carbon dioxide.
The usefulness of the alkali alkylcarbonates in the carboxylation of alkali phenoxides is described. Furthermore, a convenient preparation method of the alkali alkylcarbonates from alcohol, alkali phenoxide and carbon dioxide is also described.
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