Revisiting the Kolbe–Schmitt reaction of sodium 2-naphthoxide

Abstract

The mechanism of the carboxylation reaction of sodium 2-naphthoxide (NaphONa) was investigated in the positions 1, 3, and 6 by means of three methods: B3LYP, B3LYP-D2, and M06-2X. While B3LYP failed to describe reaction pathways 3 and 6, B3LYP-D2 (owing to the empirical correction term) and M06-2X (owing to the way it has been parameterised) produced relatively consistent results which create completely new picture of the reaction mechanism. It was found that the reactants can build two NaphONa–CO2 complexes, of which only one can be further transformed to the reaction products. In this new NaphONa–CO2 complex, the CO2 moiety is perfectly positioned to perform electrophilic attacks on all three nucleophilic carbons of the naphthalene ring. Each reaction pathway occurs via two transition states and one intermediate. The mechanism involves a bimolecular reaction step for proton transfer, which requires notably smaller activation barrier than previously considered intramolecular rearrangement. It was shown that reaction pathway 6 is unfavourable from both kinetic and thermodynamic points of view. On the other hand, pathways 1 and 3 are competitive: pathway 1 requires lower activation barriers, but pathway 3 yields the most stable reaction product. These thermochemical results are in good agreement with the experimentally determined products ratio.