1980 Volume 53 Issue 8 Pages 2195-2200
The preparation and properties of a water soluble porphyrin having functional groups, α,β,γ,δ-tetrakis[1-(2-hydroxyethyl)pyridinium-4-yl]porphine, are described. This porphyrin is water soluble from below pH 0 to above pH 14. Acid-base titration revealed the diprotonated diacid-monocation equilibrium (pK4=1.0) and the monocation-free base equilibrium (pK3=1.9) in the acidic range and the free base-monoanion equilibrium (pK2=13.0±0.2) in the basic region. The zinc, iron, and cobalt derivatives of the porphyrin were also synthesized and purified. Catalytic properties of the iron and cobalt complexes for reduction of molecular oxygen in water are reported in terms of cyclic voltammetry. The electrochemical reduction utilizing these complexes was interpreted to proceed via electrochemical catalytic regeneration mechanism as had been observed for tetrakis(1-methylpyridinium-4-yl)orphinatoiron(III). The apparent rate constants for electron transfer from the iron and cobalt porphyrins to oxygen were estimated to be 3–4×107 and 1×107 dm3 mol−1 s−1, respectively.
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