Selective oxidation of sulfides to sulfoxides by a molybdate-based catalyst using 30% hydrogen peroxide

An efficient method is reported for selective oxidation of various types of sulfides to sulfoxides and sulfones in good to high yields using 30% H₂O₂ in the presence of catalytic amounts of molybdate-based catalyst in acetonitrile as solvent at room temperature. The catalyst can be easily recovered and reused for seven reaction cycles without considerable loss of activity.     

Chromium (III) Catalyzed Selective Oxidation of Sulfides to Sulfoxides Using 30% H2O2

Chromium (III) is used as an efficient, recyclable catalyst for selective oxidation of sulfides. The reactions were carried out in 60% acetonitrile (v/v) using 30% H₂O₂. Chromium (III) forms complex with sulfides which is then oxidized by H₂O₂ to form sulfoxides.     

VO(acac)2 Supported on Titania: A Heterogeneous Protocol for the Selective Oxidation of Sulfides Using TBHP

The facile catalytic oxidation of sulfides to sulfoxides has been achieved with VO(acac)₂ supported on titania using tert-butyl hydroperoxide (TBHP) as an oxidant in dichloromethane in quantitative yields at room temperature. The catalyst is reusable and tested for five cycles without significant loss of activity and selectivity.     

Schiff base complex of Cu immobilized on MCM-41 as reusable catalyst for efficient oxidative coupling of thiols and oxidation of sulfides using hydrogen peroxide

Schiff base complex of copper-functionalized MCM-41 (Cu-complex@MCM-41) was synthesized and used as an efficient and novel heterogeneous catalyst for the oxidative coupling of thiols into corresponding disulfides and oxidation of sulfides to sulfoxides using hydrogen peroxide (H₂O₂) as the oxidant. An aliphatic and aromatic series of sulfides and thiols including various functional groups were successfully converted into corresponding products. The all products were obtained in good to excellent yields. The mesoporous catalyst is characterized by FT-IR spectroscopy, BET, XRD, SEM, EDS and TGA. Recovery of the catalyst is easily achieved by simple filtration and reused for several consecutive runs without significant loss of its catalytic efficiency.     

Oxidation of sulfides to sulfoxides with H2O2/HNO3 reagent system

Selective oxidation of sulfides to sulfoxides is achieved by H₂O₂ using HNO₃ as the promotor. Aromatic and aliphatic sulfides are oxidized to sulfoxides in excellent yields and short reaction times. Different functional groups including C–C double bond, ester, ketone, acetal, alcohol, and oxime groups are tolerated under this reaction condition.     

SSITKA studies of the catalytic flameless combustion of methane

This paper presents results which were obtained for the flameless combustion of methane over the Pd(PdO)/Al₂O₃ catalyst by using the steady state isotopic transient kinetic analysis method. During the reaction switches between ¹⁶O₂/Ar/CH₄/He and ¹⁸O₂/CH₄/He were carried out. The obtained results indicate the presence of large amounts of oxygen as well as of intermediates leading to the formation of carbon dioxide on the surface of the palladium catalyst. Additionally, information was obtained proving that the complete oxidation of methane over Pd/Al₂O₃ catalyst proceeds according to the Mars and van Krevelen redox mechanism. With the increase of the reaction temperature there is an increase in the number of active centres on the Pd(PdO)/Al₂O₃ catalyst surface—a larger amount of oxygen from the lattice of the catalyst is accessible for the reaction of methane oxidation.     

Asymmetric Sulfoxidation of Thioethers with Hydrogen Peroxide in Water Mediated by Platinum Chiral Catalyst

Easy stereoselective oxidation of prochiral aryl alkyl sulfides 2 to the corresponding sulfoxides can be achieved in water‐surfactant medium with inexpensive hydrogen peroxide mediated by the chiral platinum diphosphine complex {[(R)‐BINAP]Pt(μ‐OH)}₂(BF₄)₂ ( 1 ). Remarkable key features of general interest are (i) easy isolation of the products from catalyst by simple diethyl ether/water‐surfactant two phase separation, (ii) catalyst loading as low as 1% mol, (iii) good yields, sulfoxide 3 to sulfone 4 ratio up to 200 : 1 and enantioselectivities up to 88%, (iv) mild experimental conditions.     

Silica sulfuric acid promoted selective oxidation of sulfides to sulfoxides or sulfones in the presence of aqueous H2O2

Alkyl and aryl sulfides are oxidized to the corresponding sulfoxides or sulfones in excellent yields with aqueous hydrogen peroxide in the presence of silica sulfuric acid as an efficient solid acid catalyst. The oxidation of alkyl and aryl sulfide proceeds at 25–90°C and the corresponding sulfoxides or sulfones was selectively obtained by controlling the amounts of H₂O₂ and catalyst.     

Synthesis,X-ray structure and study of a mixed ligand iron(III) complex with tridentate Schiff base as a homogeneous catalyst in the efficient oxidation of sulfides

A mononuclear mixed ligand complex of iron, [Fe^III(N-OPh-sal)(acac)EtOH], where Hacac and N-HOPh-Hsal denote acetylacetone and N-hydroxyphenyl-salicylideneamine, respectively, has been synthesized and characterized by elemental analysis, spectral studies and X-ray crystallography. The catalytic system containing this complex and urea hydrogen peroxide as oxidizing agent was used to selectively oxidize a range of sulfides to the corresponding sulfoxides in good yields under mild conditions. The electronic spectra of the catalytic system were applied to explore reactivity and stability of the catalyst during sulfide oxidation reactions and to examine the nature of active species, as well.     

Zr (IV)-ninhydrin supported MCM-41 and MCM-48 as novel nanoreactor catalysts for the oxidation of sulfides to sulfoxides and thiols to disulfides

Modification of MCM-41 and MCM-48 mesoporous materials with bonded aminosilane species, Schiff base preparation by ninhydrin and finally complexation with zirconium, has attracted much attention in order to design catalyst with advanced applications in the oxidation of sulfides to sulfoxides and thiols to disulfides in the presence of hydrogen peroxide. In all oxidation of sulfides to sulfoxids 0.4 mL H₂O₂ used as oxidant in the presence of Zr(IV)-ninhydrin supported MCM-41 (0.01 g) or Zr(IV)-ninhydrin supported MCM-48 (0.005 g) at room temperature and solvent-free condition. Also the best conditions for oxidation of thiols to disulfides with 0.4 mL H₂O₂ were 0.005 g Zr(IV)-ninhydrin supported MCM-41 or Zr(IV)-ninhydrin supported MCM-48 at room temperature and in ethanol. These catalysts are characterized by SEM, XRD, TGA, FT-IR, EDS, ICP and BET analysis. Also the Turn over frequency (TOF) and Turn over number (TON) of catalysts are calculated. Obtained results by these heterogeneous catalysts revealed several advantages including short reaction times, simple workup, easy isolation and reusability.     

I2 as a mild and efficient catalyst in deoxygenation of sulfoxides with thioacetic acid

An effective procedure for deoxygenation of sulfoxides to sulfides using thioacetic acid as a reducing agent and a catalytic amount of I₂ in MeCN at ambient temperature has been developed. Using this protocol, a variety of sulfoxides including benzyl, allyl, alkyl and aryl sulfoxides have been successfully reduced to the corresponding sulfides in excellent yields.     

DABCO tribromide immobilized on magnetic nanoparticle as a recyclable catalyst for the chemoselective oxidation of sulfide using H2O2 under metal- and solvent-free conditions

Magnetic nanoparticle-supported 1,4-diazabicyclo[2.2.2] octane tribromide (MNPs-DABCO tribromide) as a bromine source was readily prepared and characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM) techniques. The catalytic activity of MNPs-DABCO tribromide was investigated in the chemoselective oxidation of sulfides to sulfoxides using 30% H₂O₂ as an oxidant at room temperature under solvent-free conditions. The heterogeneous catalyst could be recovered easily and reused 15 times without significant loss of its catalytic activity.     

N2O Decomposition Catalysed by Transition Metal Ions

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al₂O₃), reduced nickel catalyst (Ni⁰/Al₂O₃), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al₂O₃) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH₄/O₂ reaction, even with a pre-reduced nickel catalyst, and Ni⁰ is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni⁰ is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.     

Highly efficient selective oxidation of sulfides to sulfoxides by montmorillonite-immobilized metalloporphyrins in the presence of molecular oxygen

Highly efficient and selective oxidation of sulfides to sulfoxides with dioxygen catalyzed by cationic meso-tetrakis (1-methyl-4-pyridyl) (TM4PyP) metalloporphyrins immobilized into montmorillonite (MT) interlayer was achieved. Manganese (II) porphyrin (MnTM4PyP-MT) presented excellent activity for the oxidation of sulfides under ambient conditions. In the model oxidation, thioanisole was converted completely and the selectivity towards sulfoxide was up to 95%. This catalyst also showed high activity and selectivity for the most sulfides. The catalyst could be reused consecutively five times without significant loss of activity.     

The deep oxidation of chemical warfare agent models: facile catalytic oxidative cleavage of phosphorus-carbon and sulfur-carbon bonds using dioxygen

In water, metallic palladium on carbon was found to catalyze the deep oxidation of organophosphorus and organosulfur compounds by dioxygen at 90°C in the presence of carbon monoxide. This system presents the first examples of catalytic cleavage of phosphorus-carbon bonds. Starting with trimethylphosphine oxide, the phosphorus-containing products formed by sequential P-C cleavage were dimethylphosphinic acid, methylphosphonic acid, and phosphoric acid. A similar reaction sequence was also observed for triethylphosphine oxide, except that products formed by partial oxidation of the ethyl groups, such as phosphonoacetic acid, were also seen as intermediates. The deep oxidation of dimethyl and diethyl sulfides proceeded through the intermediacy of the corresponding sulfoxides. For the methyl derivatives, the ease of oxidation decreased in the order: (CH₃)₂S>(CH₃)₂S O>(CH₃)₂SO₂ and is consistent with the system acting as an electrophilic oxidant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective and efficient oxidation of sulfides and thiols with a 1,1,3,3-tetramethylguanidine/Br2 complex

The 1,1,3,3-tetramethylguanidine/Br₂ complex has been found to be an efficient reagent for the selective oxidation of aliphatic and aromatic sulfides to the corresponding sulfoxides and the oxidative coupling of thiols to disulfides. 1,1,3,3-Tetramethylguanidine can be recovered at the completion of the reaction and reused.     

Improvement of anhydrous catalyst stability in acetylene dimerization by regulating acidity

BACKGROUND: Loss of the active CuCl component occurs during acetylene dimerisation to monovinylacetylene (MVA) catalysed by an anhydrous catalyst with the formation of a dark red precipitate. Acidic species can reduce the loss of CuCl but have an unfavorable influence on acetylene dimerisation. This study aims to determine the precipitate composition and regulate the acidity of the catalyst to find a balance between reaction rate, MVA selectivity and catalyst life. RESULT: The precipitate composition was 2CuCl·3C₂H₂·1/3CH₃CH₂NH₂·1/7C₃H₇NO, formed by the combination of DMF, CH₃CH₂NH₂, C₂H₂ and the [Cu]‐acetylene π‐complex, which is an intermediate in the reaction. From an overall consideration of the loss of CuCl, conversion of acetylene, and selectivity of MVA, the reaction temperature and acetylene space velocity were optimized at 65 °C and 200 h^?1, respectively. The introduction of HCl into the catalyst with a rate of 3.2 h^?1 could reduce CuCl loss by 73.5%, whereas conversion of acetylene was only lowered by 9.0%. CONCLUSION: Acidity regulation of the anhydrous catalyst by optimising the reaction temperature, acetylene space velocity, and rate of addition of HCl shows little negative effect on acetylene conversion and selectivity to MVA but can reduce CuCl loss significantly. © 2012 Society of Chemical Industry     

Transient response of catalyst bed temperature in the pulsed reaction of partial oxidation of methane to synthesis gas over supported group VIII metal catalysts

Mechanisms of partial oxidation of methane to synthesis gas were studied using a pulsed reaction technique and temperature jump measurement. Catalyst bed temperatures were directly measured by introducing 1 and 3 ml pulses of a mixture of CH₄ and O₂ (2/1). With Ir, Pt and Ni/TiO₂ catalysts, a sudden temperature increase at the front edge of the catalyst bed was observed upon introduction of the pulse. The synthesis gas production basically proceeded via two-step paths consisting of highly exothermic complete methane oxidation to give H₂O and CO₂, followed by the endothermic reforming of methane with H₂O and CO₂. In contrast, with the Rh and Pd/TiO₂ catalysts, the temperature at the front edge of the catalyst bed decreased upon introduction of the CH₄/O₂ (2/1) pulse and a small increase in the temperature at the rear end was observed. Initially, the endothermic decomposition of CH₄ to H₂ and deposited carbon or CH_x probably took place at the front edge of the catalyst bed, after which the deposited carbon or generated CH_x species would be oxidized into CO_x. When the Ru/TiO₂ catalyst was used, a temperature increase at the front edge of the catalyst bed was observed upon introduction of the 3 ml pulse of CH₄/O₂. In contrast, the temperature drop at the front edge of the catalyst bed was observed for a 1 ml pulse of CH₄/O₂. These results seemed to exhibit two possibilities for a synthesis gas formation route over the Ru/TiO₂ catalyst. The reaction pathway of the partial oxidation of methane with group VIII metal-loaded catalysts depended strongly upon the metal species and reaction conditions.     

Role of the surface state of Ni/Al2O3 in partial oxidation of CH4

The effect of gas phase O₂ and reversibly adsorbed oxygen on the decomposition of CH₄ and the surface state of a Ni/Al₂O₃ catalyst during partial oxidation of CH₄ were studied using the transient response technique at atmospheric pressure and 700°C. The results show that, when the catalyst surface is completely oxidized under experimental conditions, only a small amount of CO and H₂ can be produced from non‐selective oxidation of CH₄ by reversibly adsorbed oxygen which is more active in oxidizing CH₄ completely than NiO via the Rideal–Eley mechanism and both the conversions of CH₄ and O₂ and the selectivities to CO and H₂ are very low. Therefore, keeping the catalyst surface in the reduced state is the precondition of high conversion of CH₄ and high selectivities to CO and H₂. The surface state of the catalyst decides the reaction mechanism and plays a very important role in the conversions and selectivities of partial oxidation of CH₄. During partial oxidation of CH₄, no oxygen species but a small amount of carbon exists on the catalyst surface, which is favorable for maintaining the catalyst in the reduced state and the selectivity of CO. The results also indicate that direct oxidation is the main route for partial oxidation of CH₄, and the indirect oxidation mechanism is not able to gain dominance in the reaction under the experimental conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation of chiral oxovanadium (IV) Schiff base complex functionalized by ionic liquid for enantioselective oxidation of methyl aryl sulfides

Chiral oxovanadium (IV) Schiff base complex covalently grafted with ionic liquid (IL: 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate) has been reported first time. The IL-functionalized complex was found to be an efficient catalyst in the enantioselective oxidation of methyl aryl sulfides to sulfoxides with hydrogen peroxide as an oxidant. Especially, the IL-functionalized complex could be recovered conveniently by simple precipitation with addition of hexane and reused at least six cycles without loss of activity and enantioselectivity.