Kinetics and mechanism of reduction of palladium(II) complexes with ethanolamine on a dropping mercury electrode

The kinetics of electroreduction of palladium(II) complexes with ethanolamine (mea) is studied by ac and dc polarography at pH 6.2-11.5 and different ethanolamine concentrations. At c(mea) approximate to 0.3-1 M and pH 6.2, commensurate quantities of Pd(mea)(4)(2+) and Pd(mea)(3)(2+) complexes are present in solutions. The latter, as opposed to the former, contains one bidentate-coordinated ligand. The equilibrium constant for the reaction of mutual conversion of these two complexes at pH 6.2 is determined, along with the equilibrium constant for a similar reaction at pH 7.2. A diffusion nature of observed limiting currents is established. Kinetic parameters of the slow electrochemical stage are determined. The E-1/2 shift in the negative direction with pH adjusted from similar to9.5 to 11.5 is due to the preceding reversible chemical stage of protonation of the Pd(mea)(3)(H(-1)mea)(+) complexes predominant in solution in the pH interval mentioned.