Comproportionation in the reduction of pyridinium derivatives—a combined ESR and electrochemical study

• Published in: Electrochimica acta 1997, Vol.42 (12), p.1771-1780
• Main Authors: Volke, J., Dunsch, L., Volkeová, V., Petr, A., Urban, J.
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Kinetics and mechanism of reactions
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/S0013-4686(96)00407-0

Combination of voltammetry at various types of solid electrodes (mostly Pt) with electrochemical generation of radical intermediates and their ESR investigation enabled a detailed elucidation of the reduction mechanism of 1,2,4,6-tetrasubstituted pyridinium cations and of analogous 1,1′-X-hexasubstituted bipyridinium dications. The experiments were carried out in aprotic solvents such as eg dimethylformamide. The measurements confirmed the reversible stepwise one-electron reduction of the quaternary pyridinium site leading to the formation of the ESR-visible radical (or radical cation) and followed by the uptake of a further electron. These reactions result in the formation of the corresponding anion and its protonation (possibly by traces of water present in the solution). The measurement of the change in the ESR intensity with time of the radical without applied voltage revealed that the redox mechanisms of the compounds are complicated by synproportionation between the starting substance and theanion formed by the uptake of two electrons per a single pyridinium group.