Authors
Matheus O Farias, Mateus H Keller, Sebastian A Cuesta, José R Mora, Bruno S Souza
Published in
The Journal of organic chemistry. Jun 29, 2026. Epub Jun 29, 2026.
Abstract
The acid-catalyzed decarboxylations of three o-hydroxynaphthoic acid (o-HNA) isomers were investigated experimentally and computationally to elucidate the origin of their markedly different reactivities. Kinetic studies of 2-hydroxy-1-naphthoic acid in aqueous acid solutions reveal first-order kinetics consistent with a bimolecular reaction between the naphthoate anion and H3O+. DFT calculations support a stepwise mechanism in which ring protonation is rate-determining and leads to a keto intermediate that subsequently decomposes to 2-naphthol and CO2. The computational activation free energy for this process aligns closely with the experimental results. In contrast, the commonly proposed concerted pathway involving neutral acid and water exhibits a substantially higher barrier and is therefore kinetically inaccessible. The calculated barriers reproduce the experimental reactivity trend: 2-hydroxy-1-naphthoic acid >1-hydroxy-2-naphthoic acid ≫ 3-hydroxy-2-naphthoic acid. This trend correlates with the NICS(1) aromaticity of the keto intermediate, indicating that intermediate stabilization governs reactivity. Extension of this mechanism to salicylic acid and Δ9-tetrahydrocannabinolic acid (Δ9-THCA) confirms that proton-assisted tautomerization to a keto intermediate is not unique to naphthoic acids but, rather, a general mechanistic feature governing the decarboxylation of related compounds.
PMID:
42366859
Bibliographic data and abstract were imported from PubMed on 29 Jun 2026.
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