Study of the catalytic electro-oxidation of ascorbic acid on an electrode modified by macrocyclic compounds of Fe(III), Mn(III), Ni(II), and Co(II) with TBP

The catalytic properties of the macrocyclic compounds of meso-tetrakis(o-nitrophenyl)tetrabenzoporphyrin (TBP) with Fe(III), Mn(III), Ni(II), and Co(II) were examined for the electrochemical oxidation of ascorbic acid (H2A), when the coordination compounds were deposited on glassy carbon electrodes. The catalytic activity increased in the order of galssy carbon electrode<Co(II)TBP<Ni(II)TBP<Mn(III)TBP<Fe(III)TBP. Kinetic measurements of the processes were carried out. The Tafel slopes determined are 59.5 mV for Fe(III)TBP, 72.86 mV for Mn(III)TBP, 66.80 mV for Ni(II)TBP, and 68.52 mV for Co(II)TBP. For all catalysts the reaction orders with respect to H2A and H+ are 1 and −2, respectively. The mechanism of the electro-oxidation of H2A is proposed as a CE reaction.