Electrochemical Reduction of Vanadium(V)‐Cupferron Complex, VO(cupf)₂OH

Abstract

Electrochemical reduction of vanadium(V) complex with cupferron (N‐nitroso‐N‐phenylhydroxylamine), VVO(cupf)2OH, has been studied by polarography in wide potential range to verify the catalytic mechanism of electroreduction of coordinated cupferron ligand. Reduction of the complex was studied in the concentration range from 2 ⋅ 10−5 M to 10−3 M. Depending on the process conditions kinetics of catalytic reduction of coordinated cupferron is either controlled by adsorption step or governed by mixed control of diffusion and chemical reaction. Kinetic parameters of the reduction process are reported. Reduction of VVO(cupf)2OH complex is accompanied by adsorption and autoinhibition phenomena. V(II) ion in the surface bound complex of vanadium with cupferron catalyzes reduction of coordinated cupferronate ligands. In 1 mM solutions, the catalytic reduction of coordinated cupferron ligand shifts to more cathodic potentials due to formation of a monolayer of adsorbed vanadium(III)‐cupferron complexes. Reduction kinetics in the presence of tetraalkylammonium salt is consistent with multilayer cooperative adsorption of anionic vanadium(II)‐cupferron complex and tetraalkylammonium cations.