Fulvio Di Furia

Mimicking the vanadium bromoperoxidases reactions:Mild and selective bromination of arenes and alkenes in a two-phase system

Vanadium bromoperoxidases catalyze the oxidation of bromide ion by hydrogen peroxide to a bromine-equivalent intermediate. This, in turn, brominates organic molecules. The hypothesis is made that the former reaction takes place in the hydrophilic portion of the enzyme whereas the latter proceeds in a hydrophobic one in which the brominating intermediate is rapidly transferred. We have reproduced such situation by employing a two-phase (H2O/CHCl3) system. In the aqueous acid phase H2O2 and catalytic amounts of NH4VO3 are present, together with KBr. The substrates, i.e. aromatic hydrocarbons and alkenes are dissolved in CHCl3. The bromination proceeds smoothly with stirring, at 25°C, providing high yields of the corresponding brominated products.

Oxidations with peroxotungsten complexes: rates and mechanism of stoichiometric olefin epoxidations

Abstract The stoichiometric epoxidation reactions of a series of olefins with WO-(O2)2HMPT and MoO(O2)2HMPT have been studied in dichloroethane at 40 °C. The data obtained point out the superior oxidizing ability of W(VI) over Mo(VI). However, the two peroxo groups in WO(O2)2HMPT appear to react with the substrates at different rates, the transfer of the first peroxide oxygen being faster than of the second one, contrary to that observed in the behavior of MoO(O2)2HMPT. The crystal structure of WO(O2)2HMPT·H2O, determined by diffractometric techniques, does not show any significant difference compared to that reported for MoO(O2)2HMPT·-H2O, indicating that it might be difficult to correlate the solid state structures with the different behaviors experimentally observed in solution. In spite of the different features shown by the two peroxo complexes, the data collected in this investigation suggest that an identical mechanism of oxygen transfer from the two oxidants is operating. Moreover, this mechanism should not involve the occurrence of substrate-oxidant intermediates.

Metal catalysis in oxidation by peroxides part 8 [1] further insight on the mechanism of vanadium(V) catalyzed oxidation of sulphides and alkenes by hydrogen peroxide

Abstract The oxidation of p-chlorophenyl methyl sulphide, geraniol and cyclohexene with hydrogen peroxide in the presence of catalytic amounts of bis acetylacetonato oxovanadium(IV) [VaO(acac)2] in dioxane and dioxaneethanol has been studied, p-Chlorophenyl methyl sulphoxide and 2,3-epoxygeraniol are produced in quantitative yield; oxidation of cyclohexene is, on the other hand, much less selective, affording 2-cyclohexen-1-ol, 2-cyclohexen-1-one and cyclohexene oxide as major products. Kinetic studies indicate that the rate of sulphide oxidation, at relatively low hydrogen peroxide concentration, is first-order in sulphide, oxidant and catalyst whereas, at higher [H2O2]o, zero-order dependence on hydrogen peroxide is observed. Autodecomposition of H2O2, which takes place at [VaO(acac)2] much higher than that used in oxidation experiments shows zero-order dependence on [H2O2]o and second-order dependence on [VaO(acac)2]. The equilibrium formation of monoperoxovanadium(V) species as the oxidizing agent is suggested. The relevance of acid—base equilibria, involving vanadium peroxoacid, on its oxidizing efficiency is discussed, also on the ground of potentiometric experiments. The mechanism of geraniol epoxidation, which accounts for the high reactivity and regioselectivity observed, is also discussed.

Studies directed toward the prediction of the oxidative reactivity of vanadium peroxo complexes in water. Correlations between the nature of the ligands and 51V-NMR chemical shifts

The 51V-NMR spectroscopic behavior in water of a series of vanadium peroxo complexes was investigated. Monoperoxo vanadium complexes containing bidentate ligands in which the two binding sites are either oxygen atoms (O∘O ligands) or one oxygen and one nitrogen atom (N∘O ligands) and diperoxo vanadium complexes containing variously substituted pyridines or anilines were examined. A direct dependence of the magnetic shielding of the metal, measured by its 51V-NMR chemical shift, on the electronic character of the ligand was observed in all cases. For diperoxo complexes Hammett-type correlations between the 51V-NMR chemical shifts and the σ values of the substituents in the pyridine or aniline rings were established. For monoperoxo complexes, a Ramsey-type correlation between the chemical shifts and the energy of the ligand-to-metal charge transfer electronic transitions was found thus suggesting that the electron donating ability of the ligands and the energy gap HOMO-LUMO of the peroxo complexes are linearly correlated. All these observations indicate that peroxo vanadium complexes containing strongly electron donating ligands should be weak electrophilic oxidants and poor one-electron acceptors. Preliminary data concerning the reactivity of a series of peroxo vanadium species in the simple self-decomposition reaction confirm this prediction.

Enantioselective oxidation of thioethers1: An easy route to enantiopure C2 symmetrical bis-methylsulfinylbenzenes

The direct oxidation of bis-methylthioethers 1 by t-butyl hydroperoxide, titanium tetra-iso-propilate and (+)-diethyltartrate, affords the almost enantiomerically pure dl bis-methylsulfinylbenzenes 2 (e.e.⩾99%) in a process which is also characterized by a very high diastereoselectivity.

Evidence concerning peroxovanadate structures in solution and their role in catalytic oxidation process

Abstract Evidence concerning the nature of peroxometal intermediates in the oxidation of organic substrates by hydrogen peroxide or t-butyl hydroperoxide by vanadium(V) compounds is critically reviewed; it suggests formation of either metal μ-peroxoester (or peroxoacid) 2 or side-bonded peroxometal intermediates 3. Kinetic and spectroscopic data, as well as comparison with analogous systems, indicate that an entirely different situation arises in the interaction of alkyl hydroperoxides or hydrogen peroxide with the metal center, in that while alkyl hydroperoxides generate metal μ-peroxoester intermediates, H 2 O 2 produces vanadium(V)—side-bonded peroxocomplexes. It is suggested that formation constant ( K t ) values of the peroxometal species and kinetic behaviour in catalytic oxidation permit distinction between these two significantly different modes of binding of the peroxide to the metal.

Vanadium bromoperoxidases mimicking systems: Bromohydrins formation as evidence of the occurrence of a hypobromite-like vanadium complex

In the aqueous phase of a two-phase (H2OCH2Cl2) system mimicking the hydrophilic and the hydrophobic portions of vanadium dependent bromoperoxidases, (V-BrPO), a mono peroxovanadium complex, formed in situ by addition of H2O2 to NH4VO3, oxidizes Br− to a species whose nature is still largely unknown. Such species displays a bromine-like reactivity toward organic substrates dissolved in CH2Cl2. The observation that styrene, 1-methyl- and 2-methyl styrenes afford, together with dibromo-compounds, appreciable amounts of bromohydrins, suggests that a hypobromite-like species is also formed. Evidence is presented that such a species is a vanadium complex.

Asymmetric oxidation of thioethers. Optical resolution of [1,1′-binaphthalene]-2,2′-dithiol☆

Almost optically pure (e.e. > 98%) [1,1′-binaphthalene]-2,2′-dithiol (2) is obtained by resolution of racemic 2 via the transformation of the sulfidryl functions into the corresponding thioethers 3 which are asymmetrically oxidized to diastereomeric chiral monosulfoxides 4 and then reconverted into 2. The diastereo and enantioselectivity is dependent on the structure of the thioether; i.e. the dimethylthioether 3a gives two diastereomeric sulfoxides 4a in ca. 1:1 ratio, each of them in > 98% e.e., while cyclic dithioethers 3b–d afford a single diastereomeric sulfoxide 4b–d in 46–78% e.e..

Gas-liquid chromatographic method for the determination of peracids in the presence of a large excess of hydrogen peroxide

The oxidation of organic sulphides is very fast with peracids and very slow with hydrogen peroxide. Thus, addition of an excess of methyl p-tolyl sulphide to a mixture of an organic peracid and hydrogen peroxide results in the formation of methyl p-tolyl sulphoxide equimolar with the peracid. The gas-chromatographic determination of the residual sulphide, or of the produced sulphoxide, affords a quantitative evaluation of the peracid present in the mixture. The method has been applied to the determination of m-chloroperbenzoic acid and peracetic and perpropionic acids.

Synthesis of brominated compounds. A convenient molybdenum- catalyzed procedure inspired by the mode of action of haloperoxidases

Abstract A two-phase ( CHCl 3 H 2 O ) procedure for the synthesis of halogenated compounds has recently been developed. Such procedure mimics the mode of action of the enzymes haloperoxidases which contain vanadium in their active center. We have investigated the possibility to substitute vanadium with molybdenum. The molybdenum-based reactions show some advantages over the vanadium-based ones. In fact reaction times are shorter and overall yields are larger, under similar experimental conditions, both in the reaction with double bonds as well as with aromatic rings. Moreover, with double bonds, the molybdenum catalyzed process preferentially yields bromohydrins which are valuable synthetic intermediates. On the other hand, the molybdenum-catalyzed reactions show peculiar mechanistic features which deserve further investigation.