Peroxide Adduct Research Articles

Ammoximation of cyclohexanone over nanoporous TS-1 using UHP as an oxidant

Abstract Ammoximation of cyclohexanone to cyclohexanone oxime has been carried out using ammonia and urea hydrogen peroxide adducts as the oximation reagents. Effect of catalyst concentration, temperature, and molar ratio of reactants and effect of doping TS-1 with Fe has been studied to obtain the optimum conversion of cyclohexanone (CH) and selectivity to cyclohexanone oxime. The catalyst has been characterized employing the techniques of XRD, FT-IR, EDAX, SEM, AAS and Mossbauer spectroscopy with a view to confirm phase purity, stoichiometry, particle size distribution and oxidation state of Fe. The BET surface area of TS-1 catalyst was found to be 680 m2/g. A maximum conversion of about 70% of cyclohexanone with cyclohexanone oxime selectivity of 99.72% was obtained over TS-1 doped with Fe at a temperature of 40 °C and cyclohexanone to UHP molar ratio of 1:1. Reaction seems to proceed through a redox mechanism and follow hydroxylamine as well as imine routes. According to hydroxylamine route ammonia and UHP react within the TS-1 pores and produce hydroxylamine. The hydroxylamine thus formed reacts with cyclohexanone outside the pores to produce cyclohexanone oxime. In the imine route cyclohexanone and ammonia react to produce cyclohexanone imine, which is oxidized to cyclohexanone oxime. A tentative mechanism for the process has been proposed.

An Efficient and Stereoselective Dearylation of Asarinin and Sesamin Tetrahydrofurofuran Lignans to Acuminatolide by Methyltrioxorhenium/H2O2 and UHP Systems

The synthesis of stereoisomers of acuminatolide is rare and requires complex and time-consuming multistep procedures. Asarinin (1) and sesamin (2), two diasteromeric tetrahydrofurofuran lignans, are efficiently mono-dearylated by methyltrioxorhenium (MTO, I) and hydrogen peroxide (H2O2) or urea hydrogen peroxide adduct (UHP) as primary oxidant to give (-)-(7R,8'R,8R)-acuminatolide (3A) and (+)-(7S,8R,8'R)-acuminatolide (3B), respectively, in high yield and diastereoselectivity (de >98%). The oxidation of 1 was also performed with novel heterogeneous catalysts based on the heterogenation of MTO on poly(4-vinylpyridine) and polystyrene resins. In these latter cases 3A was obtained with a different yield and selectivity depending on the physical-chemical properties of the support. Cytotoxic effects of 3A and 3B in mammalian cell lines in vitro are also reported.

Identification of the Peroxy Adduct in Multicopper Oxidases by a Combination of Computational Chemistry and Extended X-ray Absorption Fine-Structure Measurements

We have developed a computational method that combines extended X-ray absorption fine structure (EXAFS) refinements with the integrated quantum mechanical and molecular mechanics (QM/MM) method. This method allows us to obtain a structure of a metal site inside a protein that is compatible with both EXAFS data and QM calculations (i.e., that is chemically reasonable). Thereby, the QM/MM calculations play the same role as MM in nearly all NMR and crystallographic refinementsEXAFS ensures that the metal−ligand distances are accurate and QM/MM fills in all the other structural data. We have used this method to show that a structure with a peroxide ion in the center of the trinuclear cluster fits experimental EXAFS data better than a structure with the peroxide ion on the side of the cluster for the peroxide adduct of multicopper oxidases.

A new dinuclear heme-copper complex derived from functionalized protoporphyrin IX

A new biomimetic model for the heterodinuclear heme/copper center of respiratory oxidases is described. It is derived from iron(III) protoporphyrin IX by covalent attachment of a Gly-L-His-OMe residue to one propionic acid substituent and an amino-bis(benzimidazole) residue to the other propionic acid substituent of the porphyrin ring, yielding the Fe(III) complex 1, and subsequent addition of a copper(II) or copper(I) ion, according to needs. The fully oxidized Fe(III)/Cu(II) complex, 2, binds azide more strongly than 1, and likely contains azide bound as a bridging ligand between Fe(III) and Cu(II). The two metal centers also cooperate in the reaction with hydrogen peroxide, as the peroxide adducts obtained at low temperature for 1 and 2 display different optical features. Support to this interpretation comes from the investigation of the peroxidase activity of the complexes, where the activation of hydrogen peroxide has been studied through the phenol coupling reaction of p-cresol. Here the presence of Cu(II) improves the catalytic performance of complex 2 with respect to 1 at acidic pH, where the positive charge of the Cu(II) ion is useful to promote O-O bond cleavage of the iron-bound hydroperoxide, but it depresses the activity at basic pH because it can stabilize an intramolecular hydroxo bridge between Fe(III) and Cu(II). The reactivity to dioxygen of the reduced complexes has been studied at low temperature starting from the carbonyl adducts of the Fe(II) complex, 3, and Fe(II)/Cu(I) complex, 4. Also in this case the adducts derived from the Fe(II) and Fe(II)/Cu(I) complexes, that we formulate as Fe(III)-superoxo and Fe(III)/Cu(II)-peroxo exhibit slightly different spectral properties, showing that the copper center participates in a weak interaction with the dioxygen moiety.

Catalytic epoxidation of cyclooctene using molybdenum(VI) compounds and urea-hydrogen peroxide in the ionic liquid [bmim]PF6

Commercially available molybdenum(VI) compounds are shown to be good catalysts in the epoxidation of cyclooctene with the urea-hydrogen peroxide adduct (UHP) in the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF6. The cyclooctene oxide was isolated by simple extraction with organic solvent and the ionic liquid-catalyst mixture recycled and reused.

Bis (Salicylaldehyde-1, 2-Phenylene Diimine)Mn(III) Chloride (Mn(III)-Salophen) Catalysed Oxidation of Thiols to Symmetrical Disulfides Using Urea Hydrogen Peroxide (UHP) as Mild and Efficient Oxidant

A variety of thiols were oxidised efficiently by a catalytic amount of Mn(III)-salophen 1 in the presence of urea hydrogen peroxide adduct 2 as a convenient and mild oxidant to afford the corresponding disulfides in high yields in quite short reaction times.

Olefin Epoxidation by the Hydrogen Peroxide Adduct of a Novel Non-heme Mangangese(IV) Complex: Demonstration of Oxygen Transfer by Multiple Mechanisms

Olefin epoxidations are a class of reactions appropriate for the investigation of oxygenation processes in general. Here, we report the catalytic epoxidation of various olefins with a novel, cross-bridged cyclam manganese complex, Mn(Me2EBC)Cl2 (Me2EBC is 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane), using hydrogen peroxide as the terminal oxidant, in acetone/water (ratio 4:1) as the solvent medium. Catalytic epoxidation studies with this system have disclosed reactions that proceed by a nonradical pathway other than the expected oxygen-rebound mechanism that is characteristic of high-valent, late-transition-metal catalysts. Direct treatment of olefins with freshly synthesized [Mn(IV)(Me2EBC)(OH)2](PF6)2 (pKa = 6.86) in either neutral or basic solution confirms earlier observations that neither the oxo-Mn(IV) nor oxo-Mn(V) species is responsible for olefin epoxidization in this case. Catalytic epoxidation experiments using the 18O labels in an acetone/water (H2(18)O) solvent demonstrate that no 18O from water (H2(18)O) is incorporated into epoxide products even though oxygen exchange was observed between the Mn(IV) species and H2(18)O, which leads to the conclusion that oxygen transfer does not proceed by the well-known oxygen-rebound mechanism. Experiments using labeled dioxygen, (18)O2, and hydrogen peroxide, H2(18)O2, confirm that an oxygen atom is transferred directly from the H2(18)O2 oxidant to the olefin substrate in the predominant pathway. The hydrogen peroxide adduct of this high-oxidation-state manganese complex, Mn(IV)(Me2EBC)(O)(OOH)+, was detected by mass spectra in aqueous solutions prepared from Mn(II)(Me2EBC)Cl2 and excess hydrogen peroxide. A Lewis acid pathway, in which oxygen is transferred to the olefin from that adduct, Mn(IV)(Me2EBC)(O)(OOH)+, is proposed for epoxidation reactions mediated by this novel, non-heme manganese complex. A minor radical pathway is also apparent in these systems.

Environment Friendly Protocol for Enantioselective Epoxidation of Non-Functionalized Alkenes Catalyzed by Recyclable Homochiral Dimeric Mn(III) Salen Complexes with Hydrogen Peroxide and UHP Adduct as Oxidants

Environment friendly oxidants e.g. H2O2 and anhydrous urea hydrogen peroxide adduct (UHP) epoxidize non-functionalized alkenes (epoxide yield 40–99%) with high enantioselectivity (up to 94% ee) in 4–15 h using two recyclable homochiral dimeric Mn(III) salen complexes in presence of PyN-oxide with the catalysts reusability several times when UHP was used as an oxidant.

Catalytic Aromatization of Hantzsch 1,4‐Dihydropyridines by Bis(salicylaldehyde‐1,2‐phenylenediimine)Mn(III) Chloride Using Urea Hydrogen Peroxide as Mild and Efficient Oxidant.

A variety of Hantzsch 1,4-dihyropyridines were oxidized efficiently by a catalytic amount of bis(salicylaldehyde-l,2-phenylenediimine)Mn(III) chloride (Mn(III)-salophen I) in the presence of urea hydrogen peroxide adduct (UHP II) as convenient and mild oxidant to afford the related pyridine derivatives in high yields at room temperature.

Monolayers of Salen Derivatives as Catalytic Planes for Alkene Oxidation in Water

Monolayers at the gas/water interface have been used as an adjustable catalytic system in which the molecular density may be modified. Mn(III)-salen complexes bearing perfluoroalkyl substituents have been organized as a Langmuir film on an aqueous subphase containing a urea/hydrogen peroxide adduct (UHP, the oxidant) and cinnamyl alcohol (the substrate). The catalytic activity of the monolayer for the epoxidation of the alkene dissolved in water has been demonstrated and the reaction kinetic investigated. For a constant area per molecule of catalyst, the reaction rate exhibits first-order dependence on oxidant concentration and zero-order dependence on alkene concentration, in agreement with the reaction orders reported for Mn(III)-salen-catalyzed epoxidation reactions carried out in solution. Furthermore, kinetic experiments suggest an enhanced activity of the catalysts assembled in a Langmuir film relative to that observed in bulk reaction. Finally, varying the molecular density of the catalyst at the gas/water interface highlights an important dependence of the catalytic activity of the layer with the mean molecular area. A strong increase of the catalytic properties of the monolayer was observed for a mean molecular area of 140-145 A2, an increase which was supposedly related to a modification of the Mn(III)-salen complex orientation at the interface upon compression. This hypothesis was supported by PM-IRRAS (polarization modulation infrared reflection adsorption spectroscopy) experiments performed in situ on the monolayer. Such results demonstrate that a soft and adjustable molecular system like a Langmuir film can be used to better understand the reactivity in various heterogeneous and/or pseudohomogeneous (such as those based on dendrimers) catalytic systems.

Organotin-oxomolybdate coordination polymers as catalysts for the epoxidation of cyclooctene

The organotin-oxomolybdate coordination polymers [(R 3Sn) 2MoO 4]· nH 2O (R = methyl, n-butyl, cyclohexyl, phenyl, benzyl) were tested as catalysts for the liquid-phase epoxidation of cyclooctene with 30% aqueous hydrogen peroxide at 35 °C and atmospheric pressure. Water, acetonitrile and dichloromethane were examined as additional co-solvents for the reaction. The catalytic results vary considerably with the nature of the tin-bound R group and the co-solvent. For all systems, cyclooctene oxide was the only observed reaction product. Apart from the trimethyltin derivative, the best results were obtained without additional co-solvent or with CH 2Cl 2, while addition of water or CH 3CN had a detrimental effect on catalytic performance. The highest turnover frequency ( 46 mol mo l Mo − 1 h − 1 ) was obtained for the system containing the tri- n-butyltin derivative as catalyst and CH 2Cl 2 as solvent. Complete conversion of the substrate was achieved for this system within 4 h. Using water instead of CH 2Cl 2 with the n-butyl catalyst reduced the catalytic activity considerably at the beginning of the reaction, although 91% conversion was achieved after 24 h. The behavior of the trimethyltin derivative was atypical in that conversion of cyclooctene was only possible when CH 3CN was used as the co-solvent. Experiments were also carried out using a urea/hydrogen peroxide adduct as a water-free source of H 2O 2. However, the catalytic activities observed were significantly lower than those obtained using aqueous H 2O 2.

Catalytic Aromatization of Hantzsch 1,4-Dihydropyridines by Bis(salicylaldehyde-1,2-phenylenediimine) Mn(III) Chloride Using Urea Hydrogen Peroxide as Mild and Efficient Oxidant

A variety of Hantzsch 1,4-dihyropyridines were oxidized efficiently by a catalytic amount of bis(salicylaldehyde-l,2-phenylenediimine)Mn(III) chloride (Mn(III)-salophen I) in the presence of urea hydrogen peroxide adduct (UHP II) as convenient and mild oxidant to afford the related pyridine derivatives in high yields at room temperature.

Oxidation of norbornene over vanadium-substituted phosphomolybdic acid catalysts and spectroscopic investigations

Oxidation of norbornene has been carried out over mono-, di- and tri-vanadium-substituted phosphomolybdic acid catalysts with aqueous hydrogen peroxide (aq. H 2O 2) as an oxidant in different solvents. Monovanadium-substituted phosphomolybdic acid catalyst was found to be better than other catalysts for the above reaction and acetonitrile was the suitable solvent. At the optimum temperature of 60 °C, the norbornene conversion was 70% and the selectivity for 2,3-epoxy norbornane was 58%. The side products were norborneols and 2-norbornanone. The lower selectivity of 2,3-epoxy norbornane with aq. H 2O 2 is attributed to the simultaneous formation of other products, norborneols and 2-norbornanone. The norborneols are formed from norbornene by acid-catalyzed reaction. Other oxidants like urea–hydrogen peroxide adduct (UHP) and tert-butyl hydrogen peroxide (TBHP) were also tested for norbornene oxidation reaction. With UHP, the conversion was almost same (69%) as that of aq. H 2O 2 reaction; however, 2,3-epoxy norbornane was the main product with >97% selectivity. Thus, the overall yield was 66.9% at 60 °C after 4 h. The high selectivity with UHP is attributed to the controlled release of H 2O 2, absence of water and less acidic nature of UHP. With TBHP the selectivity for the epoxide was >96%; however, the conversion was low (27%). A mechanism for the norbornene oxidation is believed to be proceeding via V(5+)-peroxo and V(4+)-superoxo intermediates. NMR, EPR and UV–vis spectroscopic techniques were employed to understand the reaction intermediates and reaction pathways.

Heterogeneous oxidation of pyrimidine and alkyl thioethers in ionic liquids over mesoporous Ti or Ti/Ge catalysts.

Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity.

Selective epoxidation of cyclohexene to cyclohexene oxide catalyzed by Keggin-type heteropoly compounds using anhydrous urea–hydrogen peroxide as oxidizing reagent and acetonitrile as the solvent

Abstract The epoxidation of cyclohexene catalyzed by Keggin-type heteropoly compounds (HPAs) were investigated using anhydrous urea–hydrogen peroxide adduct (UHP) as an oxidant and acetonitrile as a solvent. Among a series of Keggin-type heteropoly compounds, tris(cetylpyridinium)12-tungstophosphate (CWP) showed the highest activity. By optimizing the reaction conditions, 80% conversion of cyclohexene and 97% selectivity for cyclohexene oxide could be achieved in the UHP/CH3CN system. When aqueous 30% hydrogen peroxide (H2O2, HP) was used, the cyclohexene conversion and cyclohexene epoxide selectivity were inferior to those obtained with the UHP/CH3CN system. The reaction of UHP with CWP has been studied by UV-Vis and 31 P NMR spectroscopy, which has revealed that the Keggin-type heteropoly compounds CWP is degraded in the presence of excess UHP to form a considerable amount of phosphorus-containing species.

Eco‐Friendly Oxidative Iodination of Various Arenes with a Urea‐Hydrogen Peroxide Adduct (UHP) as the Oxidant.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Solvent‐Free Synthesis of (Dichloroiodo)arenes from Iodoarenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Zr[bis(salicylidene)ethylenediaminato]-mediated Baeyer-Villiger oxidation: stereospecific synthesis of abnormal and normal lactones.

Baeyer-Villiger oxidation of racemic bicyclic cyclobutanones with Zr[bis(salicylidene)ethylenediaminato] (salen) complex 1 as catalyst in the presence of a urea-hydrogen peroxide adduct was found to proceed enantiospecifically. The enantiotopos selection in the oxidation was governed primarily by the Zr(salen) catalyst, although migratory aptitude (methine > methylene > methyl) in Baeyer-Villiger oxidation affected the selection to a varied extent, depending on the substrate structures; one enantiomer of cyclobutanones gave exclusively a normal lactone expected from the migratory aptitude, and the other enantiomer gave an abnormal lactone preferentially, the formation of which is counter to the migratory aptitude. Furthermore, the rates of abnormal lactone formation were found to be faster than those of normal lactone formation in most of the oxidations examined. For example, the enantiomer of racemic bicyclo[3.2.0]heptan-6-one giving an abnormal lactone reacted 2.2 times faster than the other enantiomer giving a normal lactone. To our knowledge, this example of chemocatalytic Baeyer-Villiger oxidation giving an abnormal lactone in preference to a normal lactone has been previously unreported. This unusual behavior is likely to be attributable to strict control of stereoelectronic demand in Baeyer-Villiger oxidation and chiral recognition by complex 1.

Eco-friendly Oxidative Iodination of Various Arenes with a Urea-Hydrogen Peroxide Adduct (UHP) as the Oxidant

Three easy eco-friendly laboratory procedures are pre- sented for the oxidative iodination of various activated and deacti- vated arenes with molecular iodine, in the presence of UHP (percarbamide), a stable, strongly H-bonded, solid urea-hydrogen peroxide adduct as the oxidant.

A solvent-free synthesis of (dichloroiodo)arenes from iodoarenes

An efficient solid-state oxidation of iodoarenes, ArI, is described using the urea–hydrogen peroxide adduct (UHP), a stable, inexpensive, and easily handled oxidant. The reactions were complete in 15 min at 85 °C. The melts thus obtained were reacted with excess hydrochloric acid to afford crude (dichloroiodo)arenes, ArICl 2, in 64–98% yields.