Kinetics and mechanism of the oxidation of a substituted phenol by a superoxochromium(III) ion

A superoxochromium(III) ion, CraqOO2+, abstracts the hydrogen atom from the hydroxylic group of a substituted, cationic phenol (ArOH), kCrOO = 1.24 M-1 s-1 in acidic aqueous solution at 25 degrees C. The reaction has a large kinetic isotope effect, kArOH/kArOD approximately 12 and produces ArO., which also reacts with CraqOO2+ in a rapid second step, kArO = 1.26 x 10(4) M-1 s-1. The final oxidation product is an o-quinone, which was identified by its behavior on a cation-exchange resin, UV-visible spectrum, and reaction with iodide ions. This work has extended to three the types of element-hydrogen bonds that react with CraqOO2+ about 10(2) times more slowly than with CraqO2+. The mechanistic implications of these findings are discussed.