Oscillating autoxidation reaction of p-xylene in the liquid phase, catalyzed by metal oxides

Oscillatory reaction was observed during liquid-phase oxidation of p-xylene in the presence of certain transition metal oxides as catalysts. Experimental conditions under which oscillations occur and parameters influencing this behavior are described.

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The use of phase-transfer catalysis for the initiation of p-xylene oxidation

Quaternary onium salts act as phase-transfer agents for Br^– and cobalt complexes during cobalt bromide catalyzed oxidation of p-xylene with molecular oxygen in p-xylene-water system.

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- - Br^– .

     

Activity enhancement by the support in the hydrogenation of C=C bonds over polymer-supported palladium catalysts

Four synthetic ion-exchange resins (AH, BH, CH, DH) of different hydrophilic/hydrophobic properties were used as supports for heterogeneous palladium catalysts (A, B, C, D). The resins contained styrene (STY) and 2-(methacryloxy)ethylsulfonic acid (MESA) as the comonomers. Either divinylbenzene (DVB: CH, DH resins) or N,N'-methylenebisacrylamide (MBAA: AH, BH resins) were used as the cross-linker. AH contained also N,N-dimethylacrylamide (DMAA) as the third comonomer. The catalysts (Pd 0.25-0.45% w/w) were obtained by ion-exchanging the acidic forms of the resins with [Pd(OAc)2] and reducing palladium(II) with excess sodium borohydride. The use of NaBH4 also ensured the neutralization of the acidic sites of the supports. No effect of the hydrophilic/hydrophobic properties of the supports was observed in the hydrogenation of cyclohexene and 2-cyclohexen-1-one in methanol, at 25 degrees C and 0.5, 1, and 1.5 MPa, respectively. However, catalysts A and B, containing amido groups provided by either DMAA or MBAA, proved to be more active than C and D. The observed activity enhancement was directly proportional to the nitrogen/ palladium molar ratio in the catalysts. This finding suggests that amido groups promote palladium through a direct interaction with the metal surface.     

Reactivity and stability of monomeric forms of iron phthalocyanines

The effect of preparation methods of monomeric iron phthalocyanine on Mössbauer perameters and transformations was investigated. The form of iron phthalocyanine influences the reactivity and stability against oxidative destruction to iron oxides.

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Oxidation of cyclohexylamine by air to its oxime

The oxidation of cyclohexylamine was studied over tungsten, molybdenum and vanadium oxides containing catalysts supported on silica, γ-alumina or hydrotalcite in the temperature range 170°C–230°C. Depending on the catalyst and reaction conditions, the main products of the reaction are cyclohexanone oxime, cyclohexylidenecyclohexylamine or cyclohexanone. About 70% selectivity of cyclohexanone oxime formation at about 20% conversion of cyclohexylamine is obtained over tungsten catalysts. The activity of the tested catalysts usually passes through a maximum and, then, gradually decreases with time on stream. The deactivation of the catalyst is caused by the formation of tar products on the catalyst surface. The mechanism of oxidation involves formation of oxygen species on the catalyst surface which oxidizes cyclohexylamine.     

Reversed-phase high-performance liquid chromatographic method for the quantitative determination of alkylbis(2-benzothiazolylsulfen)amides

An isocratic, reversed-phase HPLC procedure was developed for the simultaneous determination of isopropyl-, tert.-butyl-, tert.-amyl-, cyclohexylbis(2-benzothiazolylsulfen)amides. Quantitation is performed on a C₁₈ bonded-phase column (Separon SGX C₁₈ 5 μm) using N-dicyclohexyl-2-benzothiazolesulfenamide as internal standard followed by UV photodiode-array detection. The precision (n = 7) for all derivatives of alkylbis(2-benzothiazolylsulfen)amides is within 1.5%. Identification of the compounds also in the mixtures was done by NMR spectroscopy.     

Hydrogenation of chloronitrobenzenes over Pd and Pt catalysts supported on cationic resins

Liquid phase hydrogenation of chloronitrobenzene isomers (x-CNB x = 2, 3, 4) to the corresponding chloroanilines (x-CAN) at mild reaction conditions (0.6 MPa, 25°C, diethyl ether-methanol as solvents) over palladium and platinum catalysts containing 1 mass % of metal on trimethylammonium functionalized poly{styrene-co-divinylbenzene} (Dowex-D) was studied. The average selectivities to x-CAN over Pd/D-Cl and Pd/D-OH catalysts were 72 % and 42 %, respectively, at the x-CNB conversion of about 80 %. The average selectivities of 81 % and 84 % were achieved using Pt/D-Cl and Pt/D-OH, respectively, at the x-CNB conversion of approximately 90 %, whereas the average starting reaction rates were 1.2 × 10^?3 mol g^?1 s^?1 and 2.6 × 10^?3 mol g^?1 s^?1 (hydrogen consumption rate per mass of platinum), respectively. Under similar reaction conditions, using palladium catalysts supported on a resin with anionic groups anchored to polymeric chains at the average reaction rate equal to 3.8 × 10^?3 mol g^?1 s^?1 (hydrogen consumption rate per mass of palladium), the selectivities from 85 % (2-CAN and 3-CAN) to 95 % (4-CAN) were achieved (Kratky et al., 2002).     

Role of transition metals during p-xylene oxidation in aqueous system

The role of transition metals in the mechanism of p-xylene oxidation has been studied in aqueous systems at 140°C and 1.0 MPa of oxygen. The reaction proceeds according to second-order kinetics in p-xylene concentration for all metals and of <0.5 order with respect to metal concentration. For the metals studied the apparent activation energies are almost the same. The results support our previous assumption that (i) the rate-determining propagation step of p-xylene oxidation in aqueous systems does not involve metal ions, (ii) direct oxidation of p-xylene by higher valent metals does not play any significant role.

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- 140°C 1,0 . - , 0,5 . . , , 1. , - , ; 2. - - .

     

Decomposition of cumene hydroperoxide in the presence of metal 1,2-dithiolate complexes

Metal 1,2-dithiolate complexes were studied as catalysts for decomposition of cumene hydroperoxide. Reaction proceeds by a two-stage process and the first stage, corresponding to destruction of the metal complex, is influenced by the type of metal and substituents on the dithiolate ligand. On average, almost two sulfur atoms in each metal chelate are oxidized to SO₂ or SO₃, which decompose the main part of hydroperoxide.

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1,2- . : . SO₂ SO₃, .

     

Direct sulfenylation of acetone with benzothiazolesulfenamides to benzothiazolylthio-substituted alkylaminopropene: synthesis and application

N-Substituted derivatives of 2-benzothiazolesulfenamides give high yields of 1-(2′-benzothiazolylthio)-2-alkylaminoprop-1-ene and 1,1-bis-(2′-benzothiazolylthio)-2-alkylaminoprop-1-ene in a reaction with acetone in the temperature range from 56°C to 70°C and in the presence of a small amount of water. The α-sulfenylated carbonyl product, 2′-benzothiazolylthiopropan-2-one, is supposed to be an intermediate of this one-pot synthesis. 1,1-Bis-(2′-benzothiazolylthio)-2-tert-butylaminoprop-1-ene has been proved an accelerator of sulfur curing of rubber composites with high processing safety.