A polarographic study of Fe(II) and Fe(III) complexes with catechol

A study of the anodic polarography of catechol in 0.100 F sodium perchlorate is presented. A new wave is observed in alkaline solutions which is different from the simple oxidation wave of catechol to ortho-quinone observed by previous workers. The importance of buffer materials is discussed and a possible explanation of the new wave is suggested. A study of the polarography behavior of Fe(II) and Fe(III) in the presence of catechol is reported. In the case of reduction of Fe(III) in the presence of catechol, two steps occur at about -1.5 and -1.8 volts (vs. SCE) at pH higher than 11.6 corresponding to one electron reduction of Fe(III) to Fe(II) and successive two electron reduction of Fe(II) to Fe(s). At lower pH these two steps are too close together to be resolved. An oxidation wave and a reduction wave are recorded for the electrolysis of Fe(II) in the presence of catechol: the oxidation wave is observed between pH 7 and 12.3. The curve showing dependence of the limiting current on pH is similar to the distribution curve of Fe(cat). It is therefore suggested that only Fe(cat) is oxidized and observed here. The reduction wave of Fe(II) in the presence of catechol is irreversible and shifted from -1.5 to -1.8 volts upon complex formation. A calculation of formation constants, 81 and 82, was achieved according to an equation which relates the shifts of halfwave potential to the formation constants.