Production of OH radicals in the autoxidation of the Fe(II)–EDTA system
The autoxidation of oxygenated solutions of Fe(II)–EDTA containing dimethyl sulfoxide (DMSO) proceeds with the participation of the OH radical. Its presence as the crucial reactive intermediate has been established by the competition method based on the formation of methanesulfinic acid from DMSO as the reference. As competitors were used guanosine, methanol, tert-butyl alcohol, acetamide, and acetonitrile, whose rate constants span a range of almost three orders of magnitude. In the absence of competitors the yield of methanesulfinic acid is between 1/5 and 1/6 of the Fe(III) formed. Other products are formic acid and formaldehyde. The process of DMSO oxidation is essentially a chain reaction initiated by the OH radical which is at the same time one in a succession of several free-radical chain carriers, and in which the EDTA complex of Fe(II) also participates.