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Oxidations by the reagent “O2–H2O2–vanadium derivative–pyrazine-2-carboxylic acid”. Part 13.† Kinetics and mechanism of the benzene hydroxylation
Abstract
It has been concluded on the basis of the kinetic study of benzene hydroxylation by the “O2–H2O2–nBu4NVO3–PCA” reagent in acetonitrile at various temperatures that the oxidation is induced by the attack of hydroxyl radical on the benzene molecule. The rate-limiting step of the reaction is the monomolecular decomposition of the complex containing one coordinated PCA molecule as well as one hydrogen peroxide molecule: VV(PCA)(H2O2) → VIV(PCA) + HOO˙ + H+. The V(IV) species thus formed reacts further in a non-limiting stage with the second H2O2 molecule to generate the hydroxyl radical: VIV(PCA) + H2O2 → VV(PCA) + HO˙ + HO−. The effective activation energy is 19 ± 3 kcal mol−1.
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