Year: 2025
Type: article
Abstract: Electrochemical reductive deoxygenation of pyridine N-oxide is investigated with particular focus on the role of proton-coupled electron transfers. A detailed analysis of cyclic voltammograms reveals that the initial electron transfer is followed by protonation of the pyridine N-oxide anion radical. Kinetic analysis reveals an unusual fifth-order dependence on the concentration of the proton donor (either water or ethanol), suggesting the involvement of a proton donor cluster in the protonation step. The resulting neutral radical represents a key bottleneck in the reaction pathway, as it can proceed via either a parent-child coupling reaction or NO bond cleavage, the latter leading to the formation of pyridine. This competition between reaction pathways allows extraction of both the rate constant for the protonation of the N-oxide radical anion and kinetic information related to the reductive NO bond cleavage. The reductive cleavage of the protonated N-oxide radical may proceed via two possible mechanisms: 1) homolytic bond cleavage followed by reduction of the hydroxyl radical, or 2) a concerted dissociative electron transfer. The observed hydrogen-bonding effects, combined with the higher driving force for the concerted pathway, support the latter mechanism, where stabilization of the departing hydroxide ion facilitates the electron transfer.
Source: ChemPhysChem
Language: English
Topic: Chemical Reaction Mechanisms
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,550
OpenAlex ID: W4414406349