Elucidation of mechanisms of organic electrode processes by spin trapping. Electroreduction of substituted pyrylium cations

• Published in: Electrochimica acta 1991, Vol.36 (1), p.73-77
• Main Authors: Klíma, J., Volke, J., Urban, J.
• Format: Article
• Language: English
• Subjects: Adsorption; Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Study of interfaces
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/0013-4686(91)85181-6

Pyrylium cations are reduced in aprotic solvents (acetonitrile) in two one-electron steps leading first to a neutral radical and to an anion after the uptake of the second electron. The neutral primary radical is only stable if the pyrane nucleus is substituted by electron-attracting substituents, in particular in position 4: in such a case the first reduction step is reversible. Otherwise the radical rapidly dimerizes and its existence cannot be proved by direct ESR spectroscopy. In this case three aromatic nitroso compounds were successfully used as spin traps for ESR spectroscopy. Their polarographic behaviour is described in this paper. These compounds are more convenient in such measurements than PBN since the ESR spectra of their adducts with the pyrylium radical better reflect the radical structure. The electrochemical generation of the radicals, their reaction with the spin trap and the measurement of the ESR spectra proper were carried out in a special cell.