A kinetic and ESR investigation of iron(II) oxalate oxidation by hydrogen peroxide and dioxygen as a source of hydroxyl radicals

TY - JOUR

T1 - A kinetic and ESR investigation of iron(II) oxalate oxidation by hydrogen peroxide and dioxygen as a source of hydroxyl radicals

AU - Park, J S

AU - Wood, P M

AU - Davies, Michael Jonathan

AU - Gilbert, B C

AU - Whitwood, A C

PY - 1997/11

Y1 - 1997/11

N2 - The reaction of Fe(II) oxalate with hydrogen peroxide and dioxygen was studied for oxalate concentrations up to 20 mM and pH 2-5, under which conditions mono- and bis-oxalate complexes (Fe[II](ox) and Fe[II](ox)2[2-]) and uncomplexed Fe2+ must be considered. The reaction of Fe(II) oxalate with hydrogen peroxide (Fe2+ + H2O2 --> Fe3+ + .OH + OH-) was monitored in continuous flow by ESR with t-butanol as a radical trap. The reaction is much faster than for uncomplexed Fe2+ and a rate constant, k = 1 x 10(4) M(-1) s(-1) is deduced for Fe(II)(ox). The reaction of Fe(II) oxalate with dioxygen is strongly pH dependent in a manner which indicates that the reactive species is Fe(II)(ox)2(2-), for which an apparent second order rate constant, k = 3.6 M(-1) s(-1), is deduced. Taken together, these results provide a mechanism for hydroxyl radical production in aqueous systems containing Fe(II) complexed by oxalate. Further ESR studies with DMPO as spin trap reveal that reaction of Fe(II) oxalate with hydrogen peroxide can also lead to formation of the carboxylate radical anion (CO2-), an assignment confirmed by photolysis of Fe(II) oxalate in the presence of DMPO.

AB - The reaction of Fe(II) oxalate with hydrogen peroxide and dioxygen was studied for oxalate concentrations up to 20 mM and pH 2-5, under which conditions mono- and bis-oxalate complexes (Fe[II](ox) and Fe[II](ox)2[2-]) and uncomplexed Fe2+ must be considered. The reaction of Fe(II) oxalate with hydrogen peroxide (Fe2+ + H2O2 --> Fe3+ + .OH + OH-) was monitored in continuous flow by ESR with t-butanol as a radical trap. The reaction is much faster than for uncomplexed Fe2+ and a rate constant, k = 1 x 10(4) M(-1) s(-1) is deduced for Fe(II)(ox). The reaction of Fe(II) oxalate with dioxygen is strongly pH dependent in a manner which indicates that the reactive species is Fe(II)(ox)2(2-), for which an apparent second order rate constant, k = 3.6 M(-1) s(-1), is deduced. Taken together, these results provide a mechanism for hydroxyl radical production in aqueous systems containing Fe(II) complexed by oxalate. Further ESR studies with DMPO as spin trap reveal that reaction of Fe(II) oxalate with hydrogen peroxide can also lead to formation of the carboxylate radical anion (CO2-), an assignment confirmed by photolysis of Fe(II) oxalate in the presence of DMPO.

KW - Cyclic N-Oxides

KW - Electron Spin Resonance Spectroscopy

KW - Ferrous Compounds

KW - Hydrogen Peroxide

KW - Hydrogen-Ion Concentration

KW - Hydroxyl Radical

KW - Kinetics

KW - Oxalates

KW - Oxalic Acid

KW - Oxidation-Reduction

KW - Oxygen

KW - Spin Labels

KW - Spin Trapping

KW - tert-Butyl Alcohol

M3 - Journal article

C2 - 9518062

SN - 1071-5762

VL - 27

SP - 447

EP - 458

JO - Free Radical Research

JF - Free Radical Research

IS - 5

ER -