Simple and efficient method for the oxidation of sulfides to sulfones using hydrogen peroxide and a Mo(VI) based catalyst

A simple and efficient method for the oxidation of sulfides to sulfones at room temperature using ammonium heptamolybdate and 30% H₂O₂ is developed. The reactions provide excellent yields within short time, also sensitive functional groups such as allyl, vinyl, propargyl, alcohol, ketone, ester, pyridine and nitrile are found to be tolerated.     

Photocatalytic oxidation of ethylene to CO2 and H2O on ultrafine powdered TiO2 photocatalysts: Effect of the presence of O2 and H2O and the addition of Pt

The complete photocatalytic oxidation of C₂H₄ with O₂ into CO₂ and H₂O has been achieved on ultrafine powdered TiO₂ photocatalysts and the addition of H₂O was found to enhance the reaction. The photocatalytic reaction has been studied by IR, ESR, and analysis of the reaction products. UV irradiation of the photocatalysts at 275 K led to the photocatalytic oxidation of C₂H₄ with O₂ into CO₂, CO, and H₂O. The large surface area of the photocatalyst is one of the most important factors in achieving a high efficiency in the photocatalytic oxidation of C₂H₄. The photoformed OH species as well as O ₂ ⁻ and O ₃ ⁻ anion radicals play a significant role as a key active species in the complete photocatalytic oxidation of C₂H₄ with O₂ into CO₂ and H₂O. Interestingly, small amount of Pt addition to the TiO₂ photocatalyst increased the amount of selective formation of CO₂ which was the oxidation product of C₂H₄ and O₂.     

Pd loaded on high silica beta support active for the total oxidation of diluted methane in the presence of water vapor

Total oxidation of diluted methane was carried out over palladium loaded on H-beta and H-ZSM-5 having different Al concentration in order to reveal the support effect of zeolites. It was found that the Al concentration had significant influence on the methane combustion activity of Pd. Especially, Pd loaded on H-beta having the lowest concentration of Al exhibited the most striking performance in that it showed superior durability and the highest activity in the presence of 10% water vapor. In marked contrast to the zeolite-supported Pd catalysts, Pd loaded on SiO₂ was substantially inactive under the same reaction conditions. Based on the Pd K-edge EXAFS coupled with TG analysis, the reason for the superior nature of high silica H-beta was attributed to the hydrophobic character of supports and the formation of agglomerated PdO, which was active in the methane combustion.     

Host (nanocavity of zeolite-Y)/guest (Mn(II), Co(II), Ni(II) and Cu(II) complexes of pentadendate Schiff-base ligand) nanocomposite materials (HGNM): application in the heterogeneous oxidation of cyclohexene

Transition metal (M = Mn(II), Co(II), Ni(II) and Cu(II)) complexes with pentadendate Schiff-base ligand; N,N′-bis(salicylidene)-2,6-pyridinediaminato, H₂[sal-2,6-py]; was entrapped in the nanocavity of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of bis(salicylaldiminato)metal(II); [M(sal)₂]-NaY; in the supercages of the zeolite, and (ii) in situ Schiff condensation of the metal(II) precursor complex with the corresponding 2,6-pyridinediamine; [M(sal-2,6-py)]-NaY. The new materials were characterised by several techniques: chemical analysis, spectroscopic methods (DRS, BET, FTIR and UV/Vis), conductometric and magnetic measurements. Analysis of the data indicates that the M(II) complexes are encapsulated in the nanodimensional pores of zeolite-Y and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. The Host–Guest Nanocomposite Materials (HGNM); [M(sal-2,6-py)]-NaY; catalyzes the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). Oxidation of cyclohexene with HGNM gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene. [Mn(sal-2,6-py)]-NaY shows significantly higher catalytic activity than other catalysts.     

Aerobic selective oxidation of (hetero)aromatic primary alcohols to aldehydes or carboxylic acids over carbon supported platinum

The synthesis of substituted benzaldehydes, benzoic acids, heterocyclic aromatic aldehydes and acids has been studied via the oxidation of the aromatic alcohols with air under mild pressure (<20 bar) at 100 °C, in the presence of a 1.95 wt.% Pt/C catalyst. The solvent was found to play the most important role in determining the selectivity of the oxidation products. Changing the solvent enabled tuning the reaction either to the aldehyde (pure dioxane), or the carboxylic acid (dioxane/aqueous solution without or with addition of sodium hydroxide). This oxidation method allowed to effectively oxidize many substituted benzylalcohols with various electron-releasing or -attracting groups (NO₂, Me, OMe, Cl, Br, OH, phenyl, …) and heterocyclic alcohols including nitrogen and sulphur atoms (2-thiophenemethanol, 2- and 4-pyridine methanol compounds).     

六(2,4,6-三溴苯氧基)环三磷腈(BPCPZ)的合成、热性能及应用

以六氯环三磷腈与2,4,6-三溴苯酚反应,制得有机磷腈化合物六(2,4,6-溴苯氧基)环三磷腈(BPCPZ).用红外、核磁、质谱及元素分析对产物结构进行了表征.研究了溶剂、原料配比、反应温度和反应时间对产物收率的影响.结果表明,合成的最佳条件是:四氢呋喃为溶剂,反应物料配比为n(三溴苯酚) ∶n(六氯环三磷腈)=6.5...     

Photocatalytic activity of TiO2-based materials for the oxidation of propene and benzene at low concentration in presence of humidity

This paper complements previous studies devoted to the photocatalytic oxidation of a low-concentration propene gaseous stream in absence of humidity using agglomerated TiO₂-based materials. These prepared agglomerated materials have shown very good oxidation activities and complete selectivity towards CO₂. The present paper analyses the role of humidity on propene oxidation, which has not been studied before, and extends the use of the prepared agglomerated photocatalysts to low concentration benzene oxidation, both in absence and presence of humidity. The obtained results have shown that humidity must be totally avoided, or kept as low as possible, to achieve high propene conversions. In the case of benzene, some insight to controversial published results is given; very low conversions together with benzene cracking on the surface of the photocatalyst occur in absence of humidity. However, the introduction of humidity leads to high conversions and avoids benzene cracking. The performance of the agglomerated photocatalyst containing a high surface area activated carbon (TiO₂/C1) must be underlined in terms of activity.     

Y型分子筛固载Cu[H4]Salpn配合物的合成、表征及催化环烷烃氧化性能

采用自由配体法制备了Y型分子筛固载席夫碱金属配合物（CuSalpn）和四氢席夫碱金属配合物（Cu[H4]Salpn）,并通过FT-IR光谱对所制备的催化剂进行了表征。催化剂样品Cu[Ht]Salpn／Y在环己烷氧化反应中较CuSalpn／Y表现出更高的催化活性。反应条件（包括溶剂、催化剂用量、反应温度和反应时间）对催化性能有较大影响。研究结果还表明,CuEHt]Salpn／Y对其它环烷烃氧化也具有较高催化活性。     

Photocatalytic oxidation of Auramine O in the presence of semiconducting oxides

The photocatalytic degradation of Auramine O, a diarylmethane fluorescent dye, has been investigated in aqueous heterogeneous solutions containing semiconductor oxides as photocatalysts. The disappearance of the organic molecule follows approximately a pseudo‐first order kinetics according to the Langmuir–Hinshelwood model. CO₂ and NH₄⁺ ions have been identified as mineralization products. Various commercial photocatalysts are compared with respect to their decolorization efficiency, as well as the production of CO₂. The effect of pH and H₂O₂ on the reaction rate is ascertained. © 2000 Society of Chemical Industry     

Catalytic oxidation of Fe(II) by activated carbon in the presence of oxygen.: Effect of the surface oxidation degree on the catalytic activity

The catalytic oxidation of Fe(II) species in aqueous solution by activated carbons with different degrees of surface oxidation is described. The parent activated carbon was oxidized with aqueous solutions of nitric acid or hydrogen peroxide, and submitted to thermal treatment at 373, 523 and 773 K. The activated carbons prepared were characterized by N₂ adsorption and temperature-programmed desorption, and their catalytic behavior was determined by measuring the oxidation rate of Fe(II) to Fe(III) and the generation of hydrogen peroxide. Catalytic activity is a function of the nature of oxygen surface groups generated by oxidation.     

Immobilization of Co(III) using tethered cyclam ligand on SBA-15 mesoporous silica for aerial oxidation of ethylbenzene

Cyclam type macrocyclic ligand was tethered onto mesoporous silica surface through N-functionalization of the cyclam. The mesoporous silica was synthesized directly with in-built chloropropyl functional group by applying microwave synthesis approach and the cyclam ligand was tethered via the surface substitution reaction of the chloro group. The tethered cyclam ligand was proven to facilely accommodate Co(III) cation into its cavity. This Co(III)cyclam-functionalized mesoporous silica showed good catalytic activity in the aerial oxidation of ethylbenzene to give acetophenone as the major product, which exceeded 60%. The presence of pyridine ligand which bounded to the axial sites of the tethered Co(III)cyclam complex enhanced the activity of the catalyst with sustaining the selectivity.     

Aerobic oxidation of alcohols catalyzed by gold nano-particles confined in the walls of mesoporous silica

Gold nano-particles confined in the walls of mesoporous silica (GMS) catalysts were successfully prepared by a novel and simple technique utilizing thioether functional groups in the walls of mesoporous silica to anchor HAuCl₄. Calcination of the materials removed organic moieties and reduced the gold salt to gold nano-particles. In this procedure, the thioether groups were introduced into the silica wall via a co-condensation of tetraethyl orthosilicate (TEOS) with 1,4-bis(triethoxysily)propane tetrasulfide. These gold containing mesoporous catalysts have unusually high surface area and pore volume. The catalysts were evaluated for the solvent free liquid phase oxidation of benzyl alcohol by molecular oxygen. High selectivity to benzaldehyde was obtained under the reaction conditions of 403 K, 15 atm and 5 h in an autoclave. The 1.5% GMS catalyst was also evaluated for oxidation of alcohols using toluene as solvent under flowing oxygen at atmospheric pressure at 353 K in a two-necked flask. Under these conditions the conversion of benzyl alcohol reached 100% after 2 h and it was demonstrated that the catalyst can be recycled three times without significant loss of activity.     

盐酸二甲胺三氧化铬／硅胶的制备及其应用

研究了盐酸二甲胺三氧化铬／硅胶的制备方法及其对醇类的氧化性能。该试剂制备简单,制备与氧化过程中均不产生含铬废液,并且性能稳定、易保存。对醇的氧化反应收率高、条件温和、操作简单。为铬（Ⅵ）氧化剂用于清洁生产提供了依据。     

Oligomeric aliphatic/aromatic poly(amides) containing silicon in the main chain and phthalimide or tetrahalophthalimide moieties as side groups

Oligomeric aliphatic poly(amides) (PAs) with phthalimide or tetrahalophthalimide were obtained from aspartic and glutamic acids which reacted previously with phthalic or tetrahalophtalic anhydrides, and the diamine bis(4-aminophenyl)-diphenylsilane, by direct polycondensation according to the Yamazaki method. PAs were characterized by IR and ¹H, ¹³C and ²⁹Si NMR, inherent viscosity measurements and optical activity. The results showed low η _inh values due to the insolubility of the PAs in the reaction media. All PAs were soluble in aprotic polar solvents and partially soluble in other common solvents as CHCl₃ and THF. The T _g values for the PAs derived from aspartic acid showed an increase when the size of the halogen atom is increased due to the more rigidity of the imide group. For those PAs derived from glutamic acid the influence of the side groups was less important due probably to the higher influence of the longer aliphatic main chain. The thermal degradation analysis showed that PAs have good TDT values with the exception of PA-7. The temperature for 50 % of weight loss for both PAs series was dependent on the nature of the halogen, showing an increase when the halogen was more electronegative. PAs do not showed good optical properties, with the exception of PA-1 and PA-6 without halogen atoms in the side chain, due to the increase of the volume of the side group which affects their mobility increasing their packing. It is possible to see a low increase of the transmittance when the aliphatic chain is increased from aspartic to glutamic acid due to an increase of the flexibility of the main chain.     

Modification of poly(vinyl alcohol) with aliphatic and aromatic epoxides in the molten phase

A new method for improving the processability and thermal stability of commercially available poly(vinyl alcohol) is presented involving the reaction of the hydroxyl group on the polymer backbone with long-chain aliphatic, cycloaliphatic, and aromatic epoxides. The reaction was performed in the molten phase using a laboratory-scale thermostated reactor. As expected, the extent of the reaction varied with the chemical structure of the epoxide, the properties of polymers obtained being dependent on the amount of the incorporated side group. Specifically, the reactivity of long aliphatic chain epoxides was low and the polymers obtained exhibited a small decrease in the melting points, being directly proportional to the length of the aliphatic chain. They displayed, however, improvement in thermal stability compared to the parent polymer. Cyclohexene oxide was appreciably more reactive and it exhibited a larger melting point reduction and satisfactory thermal stability. Polymers functionalized with aromatic rings and prepared under the same conditions were mostly amorphous, not showing melting point transition or improvement in their thermal stability. Finally, the reactions with aliphatic epoxides were catalyzed with phoshoric acid and the modified polymer exhibited a large decrease in the melting point but not a concomitant improvement in thermal stability. © 1996 John Wiley & Sons, Inc.     

Photocatalytic activity of TiO2/ZSM-5 composites in the presence of SO4 ion

TiO₂/ZSM-5 composites were prepared from SiO₂ of rice husk ash and TiO₂ sol from hydrolyzed TiOSO₄ salt. The combined effect of these two materials greatly enhanced the photocatalytic decolorization of methylene blue dye solution. The instant decolorization of the dye solution in the dark by the composite, TiO₂/ZSM-5 (wt ratio 1:1), resulted from the combination of the adsorption by ZSM-5 zeolite and TiO₂ nano-particles, and of Na₂SO₄ salt adhering to the composite surface. As a strong flocculating agent, the SO₄²⁻ ion caused the precipitation of the dye onto the composite surface which consequently enhanced the photocatalytic decolorization of the dye under UV irradiation. The composite, TiO₂/ZSM-5 (wt ratio 1:5), completely decolorized the methylene blue dye in 2.5 h, giving an equivalent performance to that of TiO₂, P-25 powder.     

Low temperature air oxidation of n-alkanes in the presence of Na-smectite

This paper is the continuation of a study concerning the catalytic effects of clay on organic matter and especially n-alkanes during oxidation carried out at low temperature. The influences of clay minerals were investigated to understand their role better during natural oxidation of organic matter.n-Alkanes oxidation experiments in presence of Na-smectite were carried out at 100 °C during 512 h and reveal an important production of oxygen-bearing molecules to the detriment of initial n-alkanes. Thus, Na-smectite allows to initiate the auto-oxidation of n-alkanes due to its chemical (charged sheets) and/or physical (high specific area) properties. The evolution of oxygen-bearing molecules distribution enables to distinguish two competitive chemical pathways. On one hand, alcohols and ketones are produced with an aliphatic chain length similar to the starting n-alkanes. On the other hand, aliphatic chain cleavages occur and principally produce 1-alcohols, 2-ketones, carboxylic acids and 3-substitued γ-lactones. These oxygen-bearing compounds are more and more preponderant and evidence the fact that cleavage mechanisms become progressively dominant.     

Electrochemical oxidation of catechol in the presence of an aromatic amine in aqueous media

The electrochemical oxidation of catechol has been studied in the presence of p-nitroaniline as a nucleophile in aqueous media at the surface of glassy carbon electrode, using cyclic voltammetry. The products of electrosynthesis have been purified and characterized by Fourier-transform infrared (FT-IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and distortionless enhancement by polarization transfer (DEPT), and the mechanism of anodic oxidation was deduced from voltammetric and spectroscopic data.