J. Technology and Education, Vol.28, No.2, pp.49-58 (2021)

総　説

 

Kolbe–Schmitt反応機構の実験および理論的研究に関する総説：

決着済みか，未解決か？

 

野口　大介

長崎大学大学院工学研究科教育研究支援部（〒852-8521　長崎県長崎市文教町1-14）

* a.chemist.noguchi.d@gmail.com

 

Experimental and Theoretical Studies on the Kolbe-Schmitt Reaction Mechanisms: Concluded or Unresolved? — A review

 

Daisuke NOGUCHI

Division of Education and Research Support, Graduate School of Engineering, Nagasaki University

(Bunkyo-machi 1-14, Nagasaki 852-8521, Japan)

 

(Received August 2, 2021; Accepted September 2, 2021)

 

Abstract

The Kolbe-Schmitt reaction is well known as a synthetic process for the industrial production of aromatic hydroxy carboxylic acids, and it is widely learned in chemical education. Several mechanistic studies of the reaction have been conducted over a century; however, it is supposed that it has not been determined yet. Therefore, the author overviews the literature focusing on its proposed reaction mechanisms, including experimental and theoretical research. In 1957, five mechanisms were reviewed: (1) metalation of aromatic nucleus, (2) intermediate formation of metal aryl carbonate, (3) direct nuclear carbonation, (4) tautomeric rearrangement, and (5) chelate formation and electrophilic substitution. After that, more intermediates of some complexes were also proposed, and X-ray crystal analyses revealed the structures of metal phenoxides (reactants) and sodium salicylate (product), both pure and/or solvated; however, it appears that the structural data were not used sufficiently to promote the mechanistic studies of the reaction. Recently, experimental studies by Kosugi et al. (Org. Biomol. Chem., 1(5), 817–821 (2003)) claimed that direct carboxylation occurs, and the complex of metal phenoxide combined with carbon dioxide is not the intermediate of the reaction; on the other hand, theoretical calculations did not support those conclusions. Further effort would be required for technological development and chemical education to integrate the accumulated knowledge of the studies of the Kolbe-Schmitt reaction mechanisms in the future.

Key words: Carbon dioxide, DFT calculation, Organic synthesis, X-ray crystallography.