Electroreduction of 1‐Methyl‐2‐, 3‐, and 4‐Carbomethoxypyridinium Ions

摘要: The character of both polarographic waves the three isomers 1‐methyl‐2‐, 3‐, and 4‐carbomethoxypyridinium ions (2+, 3+ , 4+, respectively) has been studied in acetonitrile methanol. first wave is due to a one‐electron reduction under DC normal pulse (NPP) conditions. Whereas stable free radical 4ċ reversibly formed 4+ dimer irreversibly 3+, 2+ forms 2ċ at low concentration short width equilibrium constant rate constants for dimerization reaction have determined by reverse‐pulse method (RPP). radicals identified RPP, formal potentials couples 2+/2ċ 4+/4ċ are reported. second compounds diffusion controlled protic media (methanol) yields dihydropyridine as product. In acetonitrile, pyridinium salts (n+) exhibit quite complicated behavior, which dependent on nature ion (position carbomethoxy group ring) its concentration, cations present solution, time scale electrochemical applied. isomer does not undergo step this solvent. anions 2− 4− react with form (dihydropyridines), or corresponding dimers n‐n (reaction starting material n+). latter causes decrease amplitude most favored presence indifferent bulky tetrabutylammonium cation, conditions (2− 4−) easily detected. potential 2ċ/2− 4ċ/4−