A Car–Parrinello study of the formation of oxidizing intermediates from Fenton's reagent in aqueous solution

Abstract

This paper demonstrates the spontaneous formation of the much contested ferryl ion, Fe^IVO²⁺, in an aqueous solution of iron(II) and hydrogen peroxide by means of first principles molecular dynamics simulations. Starting from hydrogen peroxide coordinated to pentaaquairon(II) in water, we show that the oxygen–oxygen bond breaks spontaneously to form [(H₂O)₅Fe^IIIOH]²⁺ and a very short-lived OH˙ radical. This radical abstracts immediately a hydrogen from a water ligand to form [(H₂O)₄Fe^IV(OH)₂]²⁺ and a water molecule. The hydrated ferryl ion [(H₂O)₅Fe^IVO]²⁺ is formed in a second step by proton donation from one OH ligand to the solvent. Starting from separated hydrogen peroxide and pentaaquairon(II) in water, we find a reactive pathway in which the ferryl ion is formed in a more direct way. As soon as H₂O₂ enters the iron(II) coordination shell, the oxygen–oxygen bond breaks and again an OH ligand and a short-lived OH˙ radical is formed. The radical abstracts the hydrogen from the OH ligand to form again the ferryl ion.