Aqueous-Phase Nitrile Hydration Catalyzed by an In Situ Generated Air-Stable Ruthenium Catalyst

RuCl₂(PTA)₄ (PTA=1,3,5-triaza-7-phosphaadamantane) is an active, recyclable, air-stable, aqueous-phase nitrile hydration catalyst. The development of an in situ generated aqueous-phase nitrile hydration catalyst (RuCl₃⋅3 H₂O+6 equivalents PTA) is reported. The activity of the in situ catalyst is comparable to RuCl₂(PTA)₄. The effects of [PTA] on the activity of the reaction were investigated: the catalytic activity, in general, increases as the pH goes up, which shows a positive correlation with [PTA]. The pH effects were further explored for both the in situ and RuCl₂(PTA)₄ catalyzed reaction in phosphate buffer solutions with particular attention given to pH 6.8 buffer. Increased catalytic activity was observed at pH 6.8 versus water for both systems with turnover frequency (TOF) up to 135 h⁻¹ observed for RuCl₂(PTA)₄ and 64 h⁻¹ for the in situ catalyst. Catalyst loading down to 0.001 mol % was examined with turnover numbers as high as 22 000 reported. Similar to the preformed catalyst, RuCl₂(PTA)₄, the in situ catalyst could be recycled more than five times without significant loss of activity from either water or pH 6.8 buffer.     

Preparation and characterization of heat-resistant PET/bio-based polyester blends for hot-filled bottles

To improve the glass transition temperature (T_g) and heat resistance of polyethylene terephthalate (PET) bottle, poly (ethylene glycol 1,4-cyclohexane dimethylene isosorbide terephthalate) (PEICT) with a unique cyclic structure was introduced into PET. The miscibility of the PET/PEICT blends and their feasibility as a heat resistant bottle were investigated. The introduction of PEICT into PET increases the T_g and the PET/PEICT blends exhibit a single T_g, indicating good miscibility between PEICT and PET. Furthermore, the T_g and crystallinity of the PET/PEICT blends can be adjusted by controlling the amount of PEICT added. The PET/PEICT blends were transparent in the visible light range (no significant change in transparency) because the blends were truly miscible as confirmed by Fox equation. As expected, the introduction of PEICT into PET bottle allows for improved heat resistance and shape stability due to the rigid molecular structure and chirality of the two tetrahydrofuran rings in the isosorbide group of PEICT. Based on our results, the as-prepared PET/PEICT blends with controllable high heat resistance can be used as a cost-effective alternative material for various hot-filling conditions in the beverage industry by adjusting the optimal ratio of PEICT to PET for each product (e.g. fruit juice, tea).     

In-Situ Formation of BHET/Titanium Compound Nanocomposite and its Catalysis for Polyester

Summary: The tetrabutylorthotitanate (TBOT) was hydrolyzed by H₂O produced during the esterification of pure terephthalic acid (PTA) and ethylene glycol (EG), and the bis(2-hydroxyethyl) terephthalate (BHET)/titanium compound nanocomposite was in-situ formed. The effect of TBOT on the esterification and its product property has been investigated. The results show that the butyl alcohol from the hydrolysis of TBOT is almost distilled out with H₂O and there has no effect on the chemical structure of BHET caused by the introducing of TBOT. A kind of novel titanium compound is manufactured during the esterification under the existence of TBOT, which shows slice-like morphology from SEM micrographs and special XRD pattern with new diffraction peaks between 2-Θ = 6.9° and 10.2°. It is found that the BHET/titanium compound nanocomposite can act as the catalyst of polymerization of poly(ethylene terephthalate) (PET). The PET resins synthesized by in-situ formed catalyst have almost the same physicochemical properties with the commerced resins and have good spinnability.     

Aqueous phase carbon dioxide and bicarbonate hydrogenation catalyzed by cyclopentadienyl ruthenium complexes

The water‐soluble ruthenium(II) complexes [Cp′RuX(PTA)₂]Y and [CpRuCl(PPh₃)(mPTA)]OTf (Cp′ = Cp, Cp*, X = Cl and Y = nil; or X = MeCN and Y = PF₆; PTA = 1,3,5‐triaza‐7‐phosphaadamantane; mPTA = 1‐methyl‐1,3,5‐triaza‐7‐phosphaadamantane) were used as catalyst precursors for the hydrogenation of CO₂ and bicarbonate in aqueous solutions, in the absence of amines or other additives, under relatively mild conditions (100 bar H₂, 30–80 °C), with moderate activities. Kinetic studies showed that the hydrogenation of HCO₃^? proceeds without an induction period, and that the rate strongly depends on the pH of the reaction medium. High‐pressure multinuclear NMR spectroscopy revealed that the ruthenium(II) chloride precursors are quantitatively converted into the corresponding hydrides under H₂ pressure. Copyright © 2007 John Wiley & Sons, Ltd.     

Efficient and Selective Formation of Unsaturated Carboxylic and Phenylacetic Acids from Diketene

A nickel catalyst promotes the multicomponent coupling reaction of diketene, an alkyne, and Me₂Zn to provide 3‐methylene‐4‐hexenoic acids in excellent yields. Under similar conditions, the combination of the nickel catalyst and Et₂Al(OEt) promotes a cycloaddition reaction involving dimerization of an alkyne to furnish phenylacetic acids. In the presence of PPh₃, a formal [2+2+1+1] cycloaddition reaction proceeds to afford regioisomeric phenylacetic acids via cleavage of the C?C bond.     

Palladium-catalyzed isomerization of 1-hexene

The isomerization of 1-hexene over Pd(acac)₂ + BF₃OEt₂ and Pd(acac)₂ + PPh₃ + BF₃OEt₂ catalyst systems proceeds by the consecutive-parallel scheme. Tetracoordinate square-planar Pd hydrides bearing two vacant coordination sites are likely to be catalytically active species for the isomerization of hexene-1. This revised version was published online in June 2006 with corrections to the Cover Date.     

H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> anchored on graphene-grafted silica-coated MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> as magnetic catalyst for Mannich reaction

In this study, a three-component nanocomposite consisted of graphene, manganese ferrite and phosphotungstic acid (PTA) has been prepared. This composite, which is designated as Graphene/MnFe₂O₄@PTA, was synthesized through anchoring of PTA–imidazolium ionic liquid on magnetic graphene sheets. The structural and magnetic properties of the fabricated nanocomposite were studied by employing FT-IR, SEM, EDX, TEM, ICP, VSM, P-XRD and BET techniques. The synthesized magnetic nanocomposite was examined as an efficient and recyclable acidic catalyst for Mannich reaction under solvent-free conditions. The products of this reaction, which are an important class of potentially bioactive compounds, were obtained with good to excellent yields, and the catalyst could be readily recycled without any significant loss of its activity.     

Phosphotungstic acid grafted zeolite imidazolate framework as an effective heterogeneous nanocatalyst for the one‐pot solvent‐free synthesis of 3,4‐dihydropyrimidinones

Phosphotungstic acid (H₃PW₁₂O₄₀, PTA) supported on ZIF‐9(NH₂) was synthesized for the first time and performed as an effective and environmental friendly catalyst in the one‐pot three component Biginelli condensation of different substituted benzaldehydes with ethyl acetoacetate and urea to afford the corresponding 3,4‐dihydropyrimidin‐2‐(1H)‐ones under solvent‐free conditions. ZIF‐9(NH₂) and the prepared nanocatalyst PTA@ZIF‐9(NH₂) were characterized by XRD, FESEM, TEM, EDX, BET, AAS, TGA, UV–Vis, and FT‐IR. After reaction, the nanocatalyst can be easily separated from the reaction mixture by centrifuge and the recovered catalyst can be reused for at least five times with a 14% reduction in yield after the fifth run. This study showed that ZIF‐9(NH₂) can be utilized as a promising support for PTA and developed a highly active, stable and reusable heterogeneous catalyst under easy reaction condition in the multi‐component organic synthesis.     

Outer-sphere oxidation of ascorbate with os(bpy)33+ incorporated in nafion coatings on graphite electrodes

The electro-oxidation of ascorbate proceeds very slowly at graphite electrodes coated with Nafion. Incorporation of Os(bpy)₃²⁺ (bpy = 2,2′-bipyridine) in the coating produces a catalyzed oxidation of ascorbate at potentials where Os(bpy)₃²⁺ is oxidized to Os(bpy)₃³⁺. Analysis of the kinetic data demonstrates that the reaction between catalyst (Os(bpy)₃³⁺) and substrate (ascorbate) proceeds only within the outermost layer of the coating at the coating/solution interface. As the substrate concentration is increased, the limiting oxidation currents at coated rotating disk electrodes do not increase as rapidly as expected on the basis of current models of the behavior of polymer coated electrodes. Some possible reasons for this deviant behavior of cast Nafion coatings are suggested. Some implications of the results on the general utility of Nafion-coated electrodes in electro-catalytic applications are presented.     

Ring-Opening 1-Amino-3-aminomethylation of Donor–Acceptor Cyclopropanes via 1,3-Diazepanes

The first ring-opening reaction of donor–acceptor cyclopropanes to give diamines is reported. For this reaction, a 1,3-bisfunctionalization was developed using cyclopropanes, triazinanes, and Sc(OTf)₃ as the catalyst, followed by treatment with acid. The reaction proceeds under very mild conditions and tolerates many functional groups. Moreover, a library of various 1,3-diazepanes, which arise as intermediates of the first formal aza-[4+3]-cycloaddition reaction with donor–acceptor cyclopropanes, was synthesized.     

Metal‐Free [2+2+2] Cycloaddition of Ynamides and Nitriles: Mild and Regioselective Synthesis of Fully Substituted Pyridines

A metal‐free trimolecular [2+2+2] cycloaddition of internal ynamides and nitriles for de novo synthesis of fully substituted pyridines is disclosed. With the versatile Brønsted acid catalyst HNTf₂, the mild intermolecular cyclotrimerization process proceeds with complementary chemoselectivity and excellent regioselectivity.     

Citronellal cyclisation over heteropoly acid supported on modified montmorillonite catalyst: effects of acidity and pore structure on catalytic activity

Citronellal cyclisation to isopulegol is an important intermediate step in the production of menthol. Several heteropoly acids (PTA) supported on modified montmorillonite (MM) catalysts were synthesized and then tested in cyclisation reactions. The prepared samples were characterized by XRD, ICP-OES, FTIR, N₂ sorption, NH₃-TPD, pyridine adsorption, amine titration and FE-SEM techniques. Effects of post-treatment were studied on montmorillonite pore structure, acidity and catalytic activity. The catalytic activity and isopulegol selectivity improved with acid-treatment and PTA loading. The amount of Lewis acidity of montmorillonite was enhanced with acid-treatment and PTA impregnation. In cyclisation, highest catalytic activity (31.87 mmol cat g^?1 min^?1) was achieved with 96% isopulegol yield in the use of 20% PTA-MM catalyst. The highest catalytic activity and selectivity were obtained in the presence of higher acidity and strong Lewis acidic sites, whereas effects of pore structure blockage seemed minor. The catalytic activity further decreased with the loss of active acidic sites (L and B) due to PTA decomposition with calcination at a higher temperature.     

Zirconia-supported phosphotungstic acid as catalyst for alkylation of phenol with benzyl alcohol

The liquid-phase alkylation of phenol with benzyl alcohol was carried out using zirconia-supported phosphotungstic acid (PTA) as catalyst. The catalysts with different PTA loadings (5–20 wt.% calcined at 750 °C) and calcination temperature (15 wt.% calcined from 650 to 850 °C) were prepared and characterized by ³¹P MAS NMR and FT-IR pyridine adsorption spectroscopy. The catalyst with optimum PTA loading (15%) and calcination temperature (750 °C) was prepared in different solvents. ³¹P MAS NMR spectra of the catalysts showed two types of phosphorous species, one is the Keggin unit and the other is the decomposition product of PTA and the relative amount of each depends on PTA loading, calcination temperature and the solvent used for the catalyst preparation. The catalysts with 15% PTA on zirconia calcined at 750 °C showed the highest Brönsted acidity. At 130 °C and phenol/benzyl alcohol molar ratio of 2 (time, 1 h), the most active catalyst, 15% PTA calcined at 750 °C gave 98% benzyl alcohol conversion with 83% benzyl phenol selectivity.     

Herstellung von fluorreichen Verbindungen der Reihe C2ClnF6−n in heterogener Katalyse

Preparation of Compounds of the Series C₂Cl_nF_6?n with High Fluor Contents by Heterogeneous Catalysis A survey is given on catalytic systems for Cl? F exchange reactions with C₂Cl₆. A catalyst is described which is formed by reaction of C₂Cl₄/Cl₂/HF on γ-Al₂O₃ in Ni reactors. Deposition of nickel proceeds by the reaction Ni(CO)₄ → Ni + 4 CO. The formation of the catalyst and the catalytic reactions which give highly fluorinated C? Cl? F compounds are discussed.     

Preparation and Characterization of Exfoliated Poly(ethyleneterephthalate)/Montmorillonite Nanocomposites Using Modified MMTs with Variable Content of Antimony Acetate

Poly(ethylene terephthalate) (PET)/montmorillonite (MMT) nanocomposite was prepared by the direct polymerization with MMTs modified with variable content of antimony acetate (Sb(OAc)₃), which was also used as catalyst polymerization. The modified MMTs (AS‐Sb‐MMT) were prepared by intercalating both Sb(OAc)₃ and amphoteric surfactant (AS) into MMT layers. Nine kinds of Sb‐MMTs [MMT treated with Sb(OAc)₃] with different Sb content were obtained, but only six kinds of PET/MMT nanocomposites could be prepared. ICPAES was used to characterize Sb content of modified MMT, XRD was used to characterize interlayer spacing, IR spectroscopy was used to characterize composition change of Sb catalyst in modified MMT and TEM was used to investigate micromorphology of PET/MMT nanocomposites. Several results are obtained, i.e., (a) Sb content of Sb‐MMT is affected by both drying temperature and washing‐drying sequence, (b) compared with Na‐MMT (unmodified MMT), the change in the interlayer spacing of Sb‐MMT is attributed to the solvent ethylene glycol (EG) rather than the intercalated or absorbed Sb(OAc)₃, (c) based on this, a model is developed to describe the swelling of Na‐MMT and modified MMT by EG and the effect of drying temperature on the interlayer spacing, (d) exfoliation state of MMT in PET matrix of nanocomposites is controlled not only by Sb content and interlayer spacing, but also by the composition of Sb catalyst in modified MMT.     

Isothermal crystallization kinetics of chain‐extended PET

The crystallization behavior of a commercial chain‐extended PET (foam grade) was evaluated and compared to that of bottle‐grade PET. Cold and melt isothermal crystallization were analyzed by using the Avrami' model. The foam grade PET showed a slower crystallization kinetic compared to the bottle‐grade PET. The Hoffman‐Lauritzen analysis showed that the energetic barriers to nucleation and molecular mobility were higher for the chain‐extended PET. This resulted in a lower nucleation rate in both cold and melt crystallization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1966–1972, 2005     

In Situ Generation of Difluoromethyl Diazomethane for [3+2] Cycloadditions with Alkynes

A novel approach to agrochemically important difluoromethyl‐substituted pyrazoles has been developed based on the elusive reagent CF₂HCHN₂, which was synthesized (generated in situ) for the first time and employed in [3+2] cycloaddition reactions with alkynes. The reaction is extremely practical as it is a one‐pot process, does not require a catalyst or the isolation of the potentially toxic and explosive gaseous intermediate, and proceeds in a common solvent, namely chloroform, in air. The reaction is also scalable and allows for the preparation of the target pyrazoles on gram scale.     

A new reforming process based on CH4 decomposition using a hydrogen-permeating membrane reactor

A new reforming process was studied using Ni/SiO₂ with a hydrogen-permeating membrane reactor. Nickel catalyst supported on SiO₂ is highly active for CH₄-H₂O-O₂ reaction in membrane reactor and the reaction close to CH₄ + 0.35O₂ + 1.3H₂O → CO₂ + 3.3H₂ proceeds at 873 K. Since the selectivity to carbon and CO₂ increased and decreased with decreasing contact time respectively, it is considered that the reaction was started by decomposition of CH₄ followed by oxidation of C and water shift reaction. Therefore, the reaction mechanism was different from so-called autothermal reforming (ATR) reaction.     

The stable hydrogen and oxygen isotope variation of water stored in polyethylene terephthalate (PET) bottles

A set of bottled waters from a single natural spring distributed worldwide in polyethylene terephthalate (PET) bottles has been used to examine the effects of storage in plastic polymer material on the isotopic composition (delta18O and delta2H values) of the water. All samples analyzed were subjected to the same packaging procedure but experienced different conditions of temperature and humidity during storage. Water sorption and the diffusive transfer of water and water vapor through the wall of the PET bottle may cause isotopic exchange between water within the bottle and water vapor in air near the PET-water interface. Changes of about +4 per thousand for delta2H and +0.7 per thousand for delta18O have been measured for water after 253 days of storage within the PET bottle. The results of this study clearly indicate the need to use glass bottles for storing water samples for isotopic studies. It is imperative to transfer PET-bottled natural waters to glass bottles for their use as calibration material or potential international working standards.     

Spherical hollow mesoporous silica supported phosphotungstic acid as a promising catalyst for α-arylstyrenes synthesis via Friedel-Crafts alkenylation

This work presents a scalable approach for preparing spherical hollow mesoporous silica with high surface area/pore volume, serving as outstanding support for supported phosphotungstic acid catalyst with much superior catalytic performance to the one on previously reported spherical mesoporous silica toward diverse transformations, ascribed to the strengthened mass transfer and the enlarged exposure degree of acidic sites to reactants those resulting from unique hollow and mesoporous morphology.