No abstract

No abstract

The rates of reaction of hydroxyl radicals with a large number of aliphatic compounds have been determined. These include carboxylate ions, alcohols, glycols, and ethers, as well as two series of substituted methanes and acetate ions. The reactivities of aliphatic compounds towards OH radicals are dependent on both the inductive and the resonance effects, as expressed by Hamrnett's a-function. The reactivities of long-chain compounds are the sum of the partial reactivities of C-H bonds a t different positions in the molecule. This corroborates the assumption that the general pattern of reactions of OH radicals with aliphatic compounds involves the abstraction of H atoms in the rate-determining step. Only in specific cases w a s a charge-transfer mechanism indicated. A general parallelism is observed between the reactions of OH radicals and those of H atoms.RATE constants for reactions of hydroxyl radicals with some aliphatic compounds, determined by competition kinetics, were recently reported-l-' It has been suggested that the RH + OH reaction involves hydrogen-abstraction in the rate-determining step,6,8-12 resulting in the formation of a R* free radical and a water molecule.

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.