New mechanistic aspects of the Fenton reaction.

The kinetics of the Fenton reaction was studied in detail. A second reaction step in the presence of excess H2O2 is attributed to formation of the complex Fe(III)(-O2H)(aq). Therefore, the reaction of Fe(H2O)(6)(2+) with Fe(III)(-O2H)(aq) in the presence of Fe(II) to form Fe(III)(aq) (k=(7.7+/-1.5) x 10(5) M(-1) s(-1)) may contribute to the overall Fenton reaction, and could account for some of the debate in the literature concerning its detailed mechanism. If this is correct for LFe(III)(-O2H)(aq) also, then it might be of significant biological importance. The activation parameters DeltaH(not equal), DeltaS(not equal), and DeltaV(not equal) for the Fenton reaction were measured under various experimental conditions, and are used in the mechanistic interpretation.