Kinetics and Mechanism of the Reaction of a Nitroxide Radical (Tempol) With a Phenolic Antioxidant

In the absence of redox-active transition metal ions, the removal of Tempol by Trolox occurs by a simple bimolecular reaction that, most probably, involves a hydrogen transfer from phenol to nitroxide. The specific rate constant of the process is small (0.1 M m 1 s m 1 ). Metals can catalyze the process, as evidenced by the decrease in rate observed in the presence of diethylenetriaminepentaacetic acid (DTPA). Furthermore, addition of Fe(II) (20 w M ferrous sulfate and 40 w M EDTA) produces a noticeable increase in the rate of Tempol consumption.