Reactions of peroxyl radicals with Fe(H2O)62+

The reactions of RO2. radicals with Fe(H2O)(6)(2+) were studied, R=H; CH3; CH2COOH; CH2CN:, CH2C(CH3)(2)OH; CH2OH; CHCl2/CCl3. All these processes involve the following reactions: Fe(H2O)(6)(2+RO2.) reversible arrow (H2O)(5)Fe-III-OOR2+ K-1 similar to250M(-1) (1) (H2O)(5)Fe-III-OOR2+H3O+/H2O --> Fe(H2O)(6)(3+) + ROOH + H2O/OH- (2) (H2O)(5)Fe-III-OOR2+ + 2Fe(H2O)(6)(2+) --> 3Fe(H2O)(6)(3+) + ROH (3) 2RO(2)(.) --> Products (4) RO2. + (H2O)(5)Fe-III-OOR2+ --> Fe(H2O)(6)(2+) + products (5) The values of k(1) and k(3) [reaction (3) is clearly not an elementary reaction] approach the ligand exchange rate of Fe(H2O)(6)(2+), i.e. these reactions follow an inner sphere mechanism and the rate determining step is the ligand exchange step. The rate of reaction (3) is several orders of magnitude faster than that of the Fenton reaction. Surprisingly enough the K-1 values are nearly independent of the redox potential of the radical and are considerably higher than calculated from the relevant redox potentials. These results indicate that the ROO- ligands considerably stabilise the Fe(III) complex, this stabilisation is smaller for radicals with electron withdrawing groups which raise the redox potential of the radical but decrease the basicity of the ROO- ligands, two effects which seem to nearly cancel each other. Finally, the results clearly indicate that reaction (5) is relatively fast and affects the nature of the final products. The contribution of these reactions to oxidation processes involving 'Fenton-like' processes is discussed. (C) 2002 Elsevier Science Inc. All rights reserved.