Oxidation Of Thioethers Research Articles

An easy synthesis of robust polymer-supported chiral 1,1′-bi-(2-naphthol)s (BINOLs): application to the catalysis of the oxidation of prochiral thioethers to chiral sulfoxides

Polystyrene beads bearing chiral 1,1′-bi-(2-naphthol) (BINOL) moieties are readily prepared by Suzuki couplings between chiral 6-bromo-1,1′-bi-(2-naphthol)s and crosslinked polystyrene beads containing phenylboronic acid residues. With this method, no protecting groups for the phenolic residues are required; any boronic acid groups that do not take part in the Suzuki coupling are removed from the support by in situ hydrolysis, and the BINOL moieties are bound to the support via strong C–C bonds. To test the performance of the new polymer-supported (PS) BINOLs, they were reacted with titanium tetraisopropoxide to give catalysts for the oxidation of aryl methyl thioethers using t-butyl hydroperoxide in tetrahydrofuran at 0 °C. The expected sulfoxides were obtained in up to 91% ee. The results obtained with the present catalysts are comparable to those obtained with PS catalysts prepared using more elaborate syntheses, and that have the catalyst moieties bound to the support by potentially labile linking groups.

Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides

Layered double hydroxides (LDH) with Mg 2+ and Al 3+ cations in the brucite-like layer and W-containing anions in the interlayer have been prepared by direct ion exchange of a MgAl-NO 3 LDH precursor with tungstate anions. The W-containing catalysts have been characterised by elemental chemical analysis, powder X-ray diffraction, Raman and UV-DR spectroscopies, thermogravimetric analysis and nitrogen adsorption. The results indicate the presence of both WO 4 2− and W 7O 24 6− anions in the interlayer gallery. The catalytic oxidation of organic sulfides and thiophene derivatives using hydrogen peroxide as oxidizing agent, in the presence of W-containing layered double hydroxide as catalyst, was investigated using various organic solvents miscible with water. It was found that W-containing LDHs are active catalysts promoting the fast oxidation of sulfur containing organic compounds with 30% H 2O 2 under very mild reaction conditions, but the catalytic activity depends on the nature of the W-containing anions. Other factors, like as the structure of the sulfur-containing organic compounds, the reaction temperature and solvent also influence the catalytic conversion.

Microalga Chlorella sorokiniana: A New Sulfoxidation Biocatalyst.

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Exposure of Self-Assembly Interiors to External Elements. A Kinetic Approach

Five cationic surfactants, each bearing a single sulfur at various locations along their chains, were adsorbed into sodium dodecyl sulfate micelles. An oxidant, periodate, was added to the system, and the subsequent rate of thioether oxidation to sulfoxide, determined by NMR, was found to be diminished (more or less equally for all sulfur loci) by 2 orders of magnitude. In contrast, rates of hydrogen peroxide oxidation were hardly perturbed by micellization. Once again, however, there was no rate dependence on sulfur location within the chains. These results are interpreted in terms of a disordered micelle in which all chain positions have roughly equivalent access to the micelle surface. The kinetic method for assessing exposure to the external medium is applicable to self-assemblies and polymer systems wherever the NMR resolution so permits.

Microalga Chlorella sorokiniana: a new sulfoxidation biocatalyst

Whole cells of the microalga Chlorella sorokiniana were evaluated in the oxidation of prochiral thioethers as regards conversion, enantiomeric excess and enantioselectivity.

Process intensification using cavitation: Optimization of oxidation conditions for synthesis of sulfone

Cavitation can be effectively used for intensification of chemical reactions due to the production of free radicals and conditions of high temperatures and pressures locally. In the present work, use of cavitation for the intensification of the synthesis of sulfone has been explored. The oxidation of thioether or sulfide to synthesize corresponding sulfone with 30% H 2O 2 as an oxidant was studied under acoustic cavitation and the results have been compared with the conventional approach based on the use of mechanical agitation. The aim has been also to optimize the different operating conditions viz. molar ratio of reactants to the oxidizing agent, type of the catalyst as well as its concentration, type of the solvent and the reactant concentration, so as to maximize the degree of intensification. It was observed that under the optimized conditions of sonication, the yield of sulfone was about five to six times higher as compared to the conventional approach of using mechanical agitation only.

Highly reactive catalysts for aerobic thioether oxidation: The Fe-substituted polyoxometalate/hydrogen dinitrate system

A new type of polyoxometalate (POM), one with a hydrogen dinitrate group associated with a d-electron-substituted polyoxometalate, Fe III[H(ONO 2) 2]PW 11O 39 5− ( 1), has been developed that catalyzes highly effective aerobic sulfoxidation (RR′S + 0.5 O 2 → RR′SO) under ambient conditions (1 atm of air at room temperature). Comparison of the rates for aerobic sulfoxidation of the mustard simulant 2-chloroethyl ethyl sulfide (CEES) catalyzed by 1 and several other species reported to be catalysts for this class of reactions, including NO +, NO 2, (NH 4) 2Ce IV(NO 3) 6 and Au IIICl 2NO 3(CH 3CN) indicate that 1 is clearly the most effective catalyst. Conversions and selectivities for the desired sulfoxide decontamination product (CEESO in these studies) are both effectively quantitative. The low or nonexistent catalytic activity of Fe II(NO)PW 11O 39 6−, Fe(NO 3) 3 and HNO 3 argues strongly that nitrosyl and nitrate derivatives of the Fe polyoxometalate and nitric acid are not species important in catalytic turnover. The techniques of single crystal X-ray diffraction, solution NMR, FTIR, TGA, DSC, cyclic voltammetry, elemental and wet chemical analyses were applied to the characterization of 1 and these are collectively consistent with the α-Keggin structure with a strongly associated hydrogen dinitrate group and a more weakly associated nitrate of crystallization.

Selective oxidation of a pyrimidine thioether using supported tantalum catalysts

Ta 2O 5–SiO 2 catalysts were prepared by a sol–gel method using tetraethyl orthosilicate (TEOS) and tantalum (V) ethoxide as the sources of silicon and tantalum, and two families of quaternary ammonium salts, [C n H 2 n+1 (CH 3) 3N]Br ( n = 14 , 16, 18) and [(C n H 2 n+1 ) 4N]Br ( n = 10 , 12, 16, 18) as surfactants. The catalysts were compared for the selective sulfoxidation of 4,6-dimethyl-2-thiomethylpyrimidine using peroxide as an oxidising agent in a range of ionic liquids and organic solvents. The sol–gel catalysts were also compared with tantalum on MCM-41 prepared by grafting. The catalysts were characterized from adsorption–desorption isotherms of N 2, XRD patterns, small-angle X-ray scattering, IR spectra from adsorbed pyridine and CDCl 3, XPS spectra, and 29Si magic angle spinning (MAS) NMR experiments. The effect of recycling on the catalyst leaching and selectivity/activity was also studied. High activities and selectivities were found in [NTf 2] − based ionic liquids and organic solvents with good recyclability of the catalyst. Tantalum was found in the solution after reaction; however, this was determined to be due to entrapment of catalyst particulates, as opposed to leaching of the active metal.

Liquid-phase oxidation of a pyrimidine thioether on Ti-SBA-15 and UL-TS-1 catalysts in ionic liquids

Ti-SBA-15 and UL-TS-1 catalysts with 1.0 and 1.5 at% Ti were tested for the liquid-phase sulfoxidation of 4,6-dimethyl-2-thiomethylpyrimidine in a range of water-miscible and immiscible ionic liquids and molecular solvents. Superior rates and selectivities with respect to the sulfoxide were found in the ionic liquids compared with the molecular solvents. The activity of the catalyst was strongly dependent on the anion–cation combination chosen; the best solvent under these conditions was [emim][BF 4]. Almost no leaching of titanium was found with Ti-SBA-15 in the ionic liquids, whereas significant leaching was observed in molecular solvents. In all solvents used, a surface rearrangement of titanium was observed after reaction, which may account for some loss in activity of the catalyst on recycle.

Selective O2 oxidation of air-sensitive lanthanocene thiolates and thioether chelate

Two unusual regioselective O2 oxidation reactions of air-sensitive lanthanocene thiolates and a thioether chelate are described, revealing a novel oxygenation pattern of thiolate ligands.

Synthetic and computational modeling of the vanadium-dependent haloperoxidases

Abstract Vanadium-dependent haloperoxidases that catalyze the halogenation of organic substrates using hydrogen peroxide to oxidize halides are a rare class of enzymes which have an absolute requirement for vanadium. In this article, we describe studies using synthetic, small-molecule analogs of the vanadium(V) active site to functionally mimic the oxidation of bromide and thioethers. In addition, we describe computational studies using density functional theory that help describe the mechanism of catalysis.

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.

Directed evolution of cyclohexanone monooxygenases: enantioselective biocatalysts for the oxidation of prochiral thioethers.

Mutational changes in cyclohexanone monooxygenases (CHMOs), for example the introduction of serine at position 432, lead to surprisingly versatile enantioselective biocatalysts that perform particularly well in the air-mediated partial oxidation of prochiral thioethers (see scheme). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2004/z460311_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Fluorous Synthesis of Disubstituted Pyrimidines.

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WO3—30% H2O2—Cinchona Alkaloids: A New Heterogeneous Catalytic System for the Asymmetric Oxidation of Sulfides and the Kinetic Resolution of Racemic Sulfoxides.

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Mild and Highly Chemoselective Oxidation of Thioethers Mediated by Sc(OTf)3.

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Fluorous synthesis of disubstituted pyrimidines.

[reaction: see text] The fluorous synthesis of disubstituted pyrimidines is carried out by attaching 2,4-dichloro-6-methylpyrimidine with 1H,1H,2H,2H-perfluorodecanethiol. The tagged substrate is substituted with 3-(trifluoromethyl)pyrazole followed by thioether oxidation and tag displacement with amines or thiols. The fluorous chain serves as a phase tag for intermediate and product purification over FluoroFlash SPE cartridges.

WO 3–30% H 2O 2–cinchona alkaloids: a new heterogeneous catalytic system for the asymmetric oxidation of sulfides and the kinetic resolution of racemic sulfoxides

WO 3-catalyzed asymmetric oxidation of thioethers and kinetic resolution of sulfoxides with 30% aq. H 2O 2 in the presence of cinchona alkaloids under heterogeneous conditions affords chiral sulfoxides in high yields with moderate to good enantioselectivities.

Mild and highly chemoselective oxidation of thioethers mediated by Sc(OTf)3.

[reaction: see text] Catalytic Sc(OTf)(3) greatly increases the efficiency of hydrogen peroxide mediated monooxidation of alkyl-aryl sulfides and methyl cysteine containing peptides. The method is high yielding, compatible with many widely used protecting groups, suitable for solid-phase applications and proceeds with minimum over-oxidation.

ChemInform Abstract: Enantioselective Oxidation of Thioethers Using Ruthenium Complexes as Chiral Auxiliaries

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