Kinetics-of-[FeII(edta)]-Oxidation-by-Molecular-Oxygen-Revisited.

Kineticsof[FeII(edta)]OxidationbyMolecularOxygenRevisited.NewEvidenceforaMultistepMechanismSabineSeibigandRudivanEldik*InstituteforInorganicChemistry,UniversityofErlangen-Nu¨rnberg,Egerlandstrasse1,91058Erlangen,GermanyReceiVedFebruary12,1997XAdetailedmechanisticstudyofthereactionof[FeII(edta)](edta)ethylenediaminetetraacetate)withmolecularoxygenwasconductedandtheoxidationkineticswereinvestigatedasafunctionof[FeII],[O2],pH,temperature,andpressure.Theobservedkineticdatainthepresenceofanexcessof[FeII(edta)]canbeaccountedforintermsofafour-stepmechanism:reactionof(I)[FeII(edta)H2O]2-withO2byasubstitution-controlledprocesstoform[FeII(edta)O2]2-;(II)electrontransfertoformanFeIII-superoxospecies;(III)subsequentsubstitutiononasecond[FeII(edta)H2O]2-anionfollowedbyelectrontransfertogive[FeIII(edta)-O22--FeIII(edta)]4-;and(IV)afastdecompositionyieldingthemonomeric[FeIII(edta)]-andH2O2,whichrapidlyreactswith[FeII(edta)].Rateandactivationparametersforsomeofthesestepsarereportedanddiscussedwithref