Electrochemical evidence of catalysis of oxygen reduction at the polarized liquid-liquid interface by tetraphenylporphyrin monoacid and diacid

Cyclic voltammetry is used to study the role of 5,10,15,20-tetraphenyl-21H,23H-porphine (H(2)TPP) in the reduction of molecular oxygen by decamethylferrocene (DMFc) at the polarized water|1,2-dichloroethane (DCE) interface. It is shown that this rather slow reaction proceeds remarkably faster in the presence of tetraphenylporphyrin monoacid (H(3)TPP(+)) and diacid (H(4)TPP(2+)), which are formed in DCE by the successive transfer of two protons from the acidified aqueous phase. A mechanism is proposed, which includes the formation of adduct between H(3)TPP(+) or H(4)TPP(2+) and O(2) that is followed by electron transfer from DMFc to the adduct leading to the observed production of DMFc(+) and to the regeneration of H(2)TPP or H(3)TPP(+), respectively. (C) 2009 Elsevier B.V. All rights reserved.