26581-25-9Relevant articles and documents
Oxidations by the reagent "O2-H2O2-vanadium derivative-pyrazine-2-carboxylic acid". Part 12. Main features, kinetics and mechanism of alkane hydroperoxidation
Shul'pin, Georgiy B.,Kozlov, Yuriy N.,Nizova, Galina V.,Suess-Fink, Georg,Stanislas, Sandrine,Kitaygorodskiy, Alex,Kulikova, Vera S.
, p. 1351 - 1371 (2007/10/03)
Various combinations of vanadium derivatives (n-Bu4NVO3 is the best catalyst) with pyrazine-2-carboxylic acid (PCA) catalyse the oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution to produce, at temperatures V(PCA)(H2O2) → VIV(PCA) + HOO. + H+. The VIV species thus formed reacts further with a second H2O2 molecule to generate the hydroxyl radical according to the equation VIV(PCA) + H2O2 → VV(PCA) + HO. + HO-. The concentration of the active species in the course of the catalytic process has been estimated to be as low as [V(PCA)H2O2] ≈ 3.3 × 10-6 mol dm-3. The effective rate constant for the cyclohexane oxidation (d[ROOH]/dt = keff[H2O2]0[V]0) is keff = 0.44 dm3 mol-1 s-1 at 40 °C, the effective activation energy is 17 ± 2 kcal mol-1. It is assumed that the accelerating role of PCA is due to its facilitating the proton transfer between the oxo and hydroxy ligands of the vanadium complex on the one hand and molecules of hydrogen peroxide and water on the other hand. For example: (pca)(O=)V ... H2O2 → (pca)(HO-)V-OOH. Such a "robot's arm mechanism" has analogies in enzyme catalysis.
