ELECTROCHEMICAL GENERATION AND REDUCTION OF ORGANIC FREE-RADICALS - ALPHA-HYDROXYBENZYL RADICALS FROM THE REDUCTION OF BENZALDEHYDE

Careful analysis of the kinetics of the electrochemical reduction of benzaldehyde in ethanolic buffers, paying particular attention to the second reduction step(s), shows that the alpha-hydroxybenzyl radicals formed upon protonation of the initial ketyl radicals are more difficult to reduce than the starting molecule. Thus, a clear example is provided of the lack of general validity of the commonly accepted view that radicals resulting from the addition of electrophiles onto anion radicals should be easier to reduce than the substrate from which they derive. There is then no general impediment to the generation and redox characterization of radicals by electrochemical means along this type of reaction sequence. The main thermodynamic and kinetic characteristics of the reduction, dimerization, and proton exchange interconversion of the alpha-hydroxybenzyl and benzaldehyde ketyl radicals are derived from the experimental data.