Hydrogen Atom Abstraction by Methyl Radicals from tert-Butyl Hydroperoxide in a Modified Fenton Reaction

Abstract Fe aq 2+ reacts with tert-butyl hydroperoxide, (CH 3 ) 3 - COOH, in air-free acidic aqueous solutions at 25° C with a rate constant k Fe = 18.7 M -1 s -1 in H 2 O and 11.7 M -1 s -1 in D 2 O. The reaction produces methyl radicals which abstract hydrogen atoms from excess (CH3)3COOH to yield CH, and (CH 3 ) 3 COO*, k Me = 1.9(±0.6) x 10 4 M -1 s -1 in H 2 O and 2.7(±0.8) x in D 2 O. The formation of alkylperoxyl radicals under air-free conditions causes the followup chemistry to approach that normally seen in the presence of air. There is no evidence for the attack of methyl radicals at the peroxo oxygen to give methanol and alkoxyl radicals (k < 2 x 10 3 M -1 s -1 ), even though this reaction is thermodynamically favored over the observed hydrogen abstraction by over 130 kJ/mol. The reaction between Fe aq 2+ and tert-butylperoxyl radicals is unusually slow, 2 x 10 2 ≤ k ≤ 5x 10 4 M -1 s -1 .