Last Step of the Para Route of the Kolbe-Schmitt Reaction

This work is an extension of our investigations of the Kolbe--Schmitt reaction mechanism. The last step in the para route of the carboxylation reaction of alkali metal phenoxides is investigated at the B3LYP/LANL2DZ level of theory. Among several examined pathways, two mechanisms are proposed: the one involving a successive rearrangement of hydrogen and the other one based on the formation of free radicals. The former pathway is energetically comparable to the last step of the carboxylation reaction in the ortho position, whereas the latter pathway requires higher activation energy. Bearing in mind that the Kolbe--Schmitt reaction is performed at high temperatures, we assume that both reaction paths are plausible.