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.

EPR spectroscopy has been employed for the direct detection of a variety of free radicals formed from reaction of Fe()-oxalate and H 2 O 2 in the presence of carbohydrates and related compounds: this system has been designed to model the proposed mode of action of brown rot fungi. The observed hyperfine splittings allow characterization of individual radicals formed at different positions in the carbohydrate rings. Relative signal intensities in steady-state spectra indicate the rapid generation of the hydroxyl radical, followed by relatively unselective attack of ؒ OH on the substrates' C-H bonds: the rapidity of oxidation by Fe() of oxygen-conjugated carbon-centred radicals (typically k 10 8 dm 3 mol Ϫ1 s Ϫ1 ) is significantly reduced if there is an eclipsing β-oxygen substituent. The relevance of these findings to cellulose-cleaving reactions of certain fungi is discussed.