Süss-Fink, Georg

2007, Kozlov, Yuriy N, Romakh, Vladimir B, Kitaygorodskiy, Alex, Buglyo, Peter, Süss-Fink, Georg, Shul'pin, Georgiy B

The vanadate anion in the presence of pyrazine-2-carboxylic acid (PCA equivalent to pcaH) efficiently catalyzes the oxidation of 2-propanol by hydrogen peroxide to give acetone. UV-vis spectroscopic monitoring of the reaction as well as the kinetics lead to the conclusion that the crucial step of the process is the monomolecular decomposition of a diperoxovanadium(V) complex containing the pca ligand to afford the peroxyl radical, HOO center dot and a V(IV) derivative. The rate-limiting step in the overall process may not be this (rapid) decomposition itself but (prior to this step) the slow hydrogen transfer from a coordinated H2O2 molecule to the oxygen atom of a pca ligand at the vanadium center: "(pca)(O)V center dot center dot center dot O2H2" -> "(pca)(HO-)V-OOH". The V(IV) derivative reacts with a new hydrogen peroxide molecule to generate the hydroxyl radical ("V-IV" + H2O2 -> "V-V" + HO- + HO center dot), active in the activation of isopropanol: HO center dot + Me2CH(OH) -> H2O + Me2C center dot(OH). The reaction with an alkane, RH, in acetonitrile proceeds analogously, and in this case the hydroxyl radical abstracts a hydrogen atom from the alkane: HO center dot + RH -> H2O + R-center dot. These conclusions are in a good agreement with the results obtained by Bell and co-workers (Khaliullin, R. Z.; Bell, A. T.; Head-Gordon, M. J. Phys. Chem. B 2005, 109, 17984-17992) who recently carried out a density functional theory study of the mechanism of radical generation in the reagent under discussion in acetonitrile.

2001, Shul'pin, Georgiy B, Kozlov, Yuriy N, Nizova, Galina V, Süss-Fink, Georg, Stanislas, Sandrine, Kitaygorodskiy, Alex, Kulikova, Vera S

2004, Shul'pin, Georgiy B, Nizova, Galina V, Kozlov, Yuriy N, Gonzalez-Cuervo, Laura, Süss-Fink, Georg

This paper describes an investigation of the alkane oxidation with hydrogen peroxide in acetonitrile catalyzed by iron(III) perchlorate (1), iron(III) chloride (2), iron(III) acetate (3) and a binuclear iron(III) complex with 1,4,7-triazacyclononane (4). The corresponding alkyl hydroperoxides are the main products. Nevertheless in the kinetic study of cyclohexane oxidation, the concentrations of oxygenates (cyclohexanone and cyclohexanol) were measured after reduction of the reaction solution with triphenylphosphine (which converts the cyclohexyl hydroperoxide to the cyclohexanol). Methane and ethane can be also oxidized with TONs up to 30 and 70, respectively. Chloride anions added to the oxidation solution with 1 activate the perchlorate iron derivative in acetonitrile, whereas the water as additive inactivates 2 in the H2O2 decomposition process. Pyrazine-2-carboxylic acid (PCA) added to the reaction mixture decreases the oxidation rate if 1 or 2 are used as catalysts, whereas compounds 3 and 4 are active as catalysts only in the presence of small amount of PCA. The investigation of kinetics and selectivities of the oxidations demonstrated that the mechanisms of the reactions are different. Thus, in the oxidations catalyzed by the 1, 3+PCA and 4+ PCA systems the main oxidizing species is hydroxyl radical, and the oxidation in the presence of 2 as a catalyst has been assumed to proceed (partially) with the formation of ferryl ion, (Fe-IV=O)(2+). In the oxidation catalyzed by the 4+PCA system (TONs attain 240) hydroxyl radicals were generated in the rate-determining step of monomolecular decomposition of the iron diperoxo adduct containing one PCA molecule. A kinetic model of the process which satisfactorily describes the whole set of experimental data was suggested. The constants of supposed equilibriums and the rate constant for the decomposition of the iron diperoxo adduct with PCA were estimated.

2003, Kozlov, Yuriy N, Gonzalez-Cuervo, Laura, Süss-Fink, Georg, Shul'pin, Georgiy B

The binuclear iron complex containing 1,3,7-triazacyclononane and acetate bridges as ligands was found to catalyze effective oxidation of alkanes by hydrogen peroxide in acetonitrile at room temperature in the presence of pyrazine-2-carboxylic acid (P) as a cocatalyst. The primary reaction products were alkylhydroperoxides, which gradually decomposed to produce the corresponding ketones (aldehydes) and alcohols. Alkane activation was caused by the attack of hydroxyl radicals on a C-H alkane bond, which resulted in the formation of alkyl radicals. Hydroxyl radicals were generated in the rate-determining step of monomolecular decomposition of the iron diperoxo adduct with one P molecule. A kinetic model of the process that satisfactorily described the whole set of experimental data was suggested. The constants of supposed equilibria and the rate constant for the decomposition of the diperoxo complex of iron with P were estimated.