Electrochemical behaviour of heterocyclic amine derivatives in media of controlled proton availability: Part I. Reduction mechanism and electron spin resonance study of 2-phenyl 4-substituted quinolines in DMF

The electroreduction of some 4-substituted 2-phenylquinolines in dimethylformamide solutions was studied by dc and ac phase selective polarography, cyclic voltammetry, controlled-potential coulometry, ESR and UV spectrometry, in the presence and absence of protonating agents.In a protic medium 2-phenylquinolines are reduced via a bielectronic polarographic step to the corresponding 1,4-dihydroquinolines. In an aprotic medium two well-defined reduction steps are observed. The first is a reversible one-electron transfer producing a stable anion radical characterized by ESR spectroscopy. The second is an irreversible one-electron transfer producing the di-anion. A multistep scheme for the reduction process consistent with the experimental results is proposed.