Polarography of piazothiol and piazoselenol in aqueous solutions

The polarographic reduction of piazothiol and piazoselenol, like that of benzofurazan, studied earlier, involves the participation of 6 electrons and the formation of ortho-phenylenediamine. The transfer of the first electron is preceded by a reversible protonation of the molecules. Hydrogen selenide formed in the reduction of piazoselenol gives the anodic wave of mercury ionization. Reducibility increases in the series: benzofurazan, piazothiol, piazoselenol in contrast to the increase in electronegativity of the key heteroatoms Se, S, O.