A KINETIC-STUDY OF THE REACTION OF TERT-BUTYL HYDROPEROXIDE WITH IRON(III) 5,10,15,20-TETRA(4-SULFONATOPHENYL)PORPHYRIN AND RELATED-COMPOUNDS AQUEOUS-SOLUTION

The kinetics of the reaction of tert-butyl hydroperoxide with three ir on(III) tetra(4-X-phenyl)-porphyrins [X = SO3- ((FeTSPP)-T-III); CO2- ((FeTCPP)-T-III); and N(+)Me(3) (Fe(III)TMAPP)] in aqueous solution ha ve been investigated using excess of obis(3-ethyl-2,3-dihydrobenzothia zole-6-sulfonate) as a one-electron oxidant trap. The reaction with (F eTSPP)-T-III is first order in [Bu(t)O(2)H] and in [(FeTSPP)-T-III] at all pH values studied (3.8-9.8). At pH greater than or equal to 6.0 t he concentration of (FeTSPP)-T-III has to be lowered to eliminate the problem of mu-oxo dimer formation and allow the kinetics of the monome r to be studied. The measured second order rate constant shows a compl ex dependence on pH that is very similar to those reported previously for sterically hindered iron(III) tetra(sulfonatophenyl)porphyrins. At tempts to measure the rate of reaction of the mu-oxo dimer of (FeTSPP) -T-III, at pH 9.2, suggest that it is unreactive towards Bu(t)O(2)H. T he reactivity of (FeTCPP)-T-III towards Bu(t)O(2)H at pH 9.2 is essent ially the same as that of (FeTSPP)-T-III. However, Fe(III)TMAPP reacts significantly more slowly both at pH 9.2 and at 4.8. This is attribut ed to the greater tendency of this iron(III) porphyrin to form mu-oxo dimers.