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-ni trophenyl)tetrabenzoporphyrin (TBP) with Fe(III), Mn(III), Ni(II), and Co(I I) were examined for the electrochemical oxidation of ascorbic acid (H,A), 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 t he 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 f or Co(II)TBP. For all catalysts the reaction orders with respect to H(2)A a nd H+ are 1 and - 2, respectively. The mechanism of the electro-oxidation o f H,A is proposed as a CE reaction. (C) 2001 Elsevier Science B.V. All righ ts reserved.