Electrochemical oxidation of 2-mercaptopyridine N-oxide on mercury electrodes in aqueous solutions

The oxidation mechanism of 2-mercaptopyridine N-oxide (NOS) is studied in aqueous media. Polarographic, classical and differential pulse, and voltammetic studies were made. The effect of pH, reactant concentration and scan rate on the electrochemical parameters is studied. The results indicate that the anionic form of NOS is oxidized at the mercury electrode to yield a radical. At pH 2 > 4.5 the dissociation of NOS precedes the electrochemical process. At low concentration values the reversible oxidation of NOS to yield the strongly adsorbed radical takes place, whereas at high concentrations this process is accompanied by the diffusional reversible oxidation. Both processes appear at different potentials due to the contribution of Delta G(ads), which has been determined from polarographic and voltammetric measurements, having a value of -7.7 kJ mol(-1). The oxidation potential of the NOS-/NOS . redox couple has been also calculated as E(0) = 274+/-5 mV vs. the Ag/AgCl/KClsat electrode.