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Effect of the Substituents on the Ligand of Iron Phthalocyanines Adsorbed on Graphite Electrodes on Their Activity for the Electrooxidation of 2‐Mercaptoethanol
Author(s) -
Aguirre María J.,
Isaacs Mauricio,
Armijo Francisco,
Basáez Luis,
Zagal José H.
Publication year - 2002
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/1521-4109(200203)14:5<356::aid-elan356>3.0.co;2-u
Subject(s) - phthalocyanine , chemistry , redox , pyrolytic carbon , ligand (biochemistry) , electrochemistry , metal , graphite , inorganic chemistry , electrode , adsorption , photochemistry , highly oriented pyrolytic graphite , standard electrode potential , organic chemistry , biochemistry , receptor , pyrolysis
We have investigated the electrocatalytic activity of five iron phthalocyanines for the electrooxidation of 2‐mercaptoethanol, with the complexes preadsorbed on a ordinary pyrolytic graphite electrode. The potential of Fe[II]/Fe[I] and Fe[III]/Fe[II] redox processes on the adsorbed phthalocyanines are shifted to more positive potentials by the effect of electron withdrawing groups −CO 2 − , −SO 3 − and −Cl and to more negative potentials by the electron‐donating methoxy group compared to −H in unsubstituted FePc. The electrocatalytic activity, measured as current at constant potential, decreases as: Fe‐octamethoxyphthalocyanine>Fe‐phthalocyanine>Fe‐tetracarboxyphthalocyanine>Fe‐tetrasulfonatedphthalocyanine>Fe‐perchlorinatedphthalocyanine. The most oxidant complex (Fe‐perchlorinatedphthalocyanine) is the least active, which is contrary to what would be expected on thermodynamic grounds. This can be attributed to the fact that the reaction proceeds via an inner‐sphere mechanism when the metal center is in state of oxidation II.