Oxo iron(IV) as an oxidative active intermediate of p-chlorophenol in the Fenton reaction: a DFT study.
Phys Chem Chem Phys
; 14(11): 3766-74, 2012 Mar 21.
Article
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| ID: mdl-22322483
ABSTRACT
Debate continues over which active species plays the role of oxidative agent during the Fenton reaction-the HOË radical or oxo iron [Fe(IV)O](2+). In this context, the present study investigates the oxidation of p-chlorophenol by [Fe(IV)O(H(2)O)(5)](2+) using DFT calculations, within gas-phase and micro-solvated models, in order to explore the possible role of oxo iron as a reactant. The results show that the chlorine atom substitution of p-chlorophenol by oxo iron is a highly stabilising step (ΔH = -83 kcal mol(-1)) with a free energy barrier of 5.8 kcal mol(-1) in the micro-solvated model. This illustrates the high oxidising power of the [Fe(IV)O(H(2)O)(5)](2+) complex. On the other hand, the breaking of the Fe-O bond, leading to the formation of hydroquinone, is observed to be the rate-determining step of the reaction. The rather large free energy barrier corresponding to this bond cleavage amounts to 10.2 and 9.3 kcal mol(-1) in the gas-phase and micro-solvated models, respectively. Elsewhere, the lifetime of the HOË radical has previously been shown to be extremely small. These facts, combined with observations of oxo iron under certain experimental conditions, suggest that oxo iron is a highly plausible oxidative species of the reaction. In addition, a trigonal bipyramidal iron complex, coordinated either by hydroxyl groups and/or by water molecules, has been found in all described mechanisms. This structure appears to be a stable intermediate; and to our knowledge, it has not been characterised by previous studies.
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MEDLINE
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Phys Chem Chem Phys
Asunto de la revista:
BIOFISICA
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QUIMICA
Año:
2012
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Article
País de afiliación:
Francia