Synthesis,characterization, and application of monodisperse gelatin-stabilized silver nanospheres in reduction of aromatic nitro compounds

Monodisperse colloidal silver nanospheres were synthesized by the reaction of silver nitrate, hydroxylammonium hydrosulphate (NH₂OH)₂ · H₂SO₄ and sodium hydroxide in the presence of gelatin as stabilizer. Colloidal nanospheres were characterized by UV-vis absorption spectroscopy, transmission electron microscopy, X-ray diffraction and dynamic light scattering. X-ray diffraction data confirmed that the silver nanospheres were crystalline with face-centered-cubic structure. Transmission electron microscopy analysis revealed the formation of homogeneously distributed silver nanoparticles of spherical morphology and size of the nanoparticles was in the range of 0.7–5.2 nm. Silver nanospheres were stable for more than two months when stored at ambient temperature. Size and size distribution were studied by varying pH, reaction temperature, silver ion concentration in feed solution, concentration of reducing agent and concentration of the stabilizing agent. Catalytic activity of silver nanospheres was tested for the reduction reaction of nitro compounds in sodium borohydride solution. Monodisperse silver nanospheres showed excellent catalytic activity towards the reduction of aromatic nitro compounds. The reduction rate of aromatic nitro compounds had been observed to follow the sequence 4-nitrophenol > 2-nitrophenol > 3-nitrophenol.     

Rapid,efficient and selective reduction of aromatic nitro compounds with hydrazine hydrate in the presence of the plain and supported platinum nanoparticles as catalysts

The current study aimed at application of the plain and supported platinum nanoparticles as a heterogenous catalyst for the reduction of aromatic nitro compounds. Monodispersed platinum nanoparticles were synthesized by reduction of H₂PtCl₆ by ethanol in the presence of polyvinyl pyrrolidone as a stabilizer, and then were immobilized on four types of zeolites. The obtained catalyst granules were characterized by X-ray diffractometry and transmission electron microscopy. The study then focused on elaboration of the catalytic activity of the nano catalysts under different operational conditions. It was found that reaction is adequately rapid at ambient temperature, and by utilizing a sufficient amount of catalyst, can be completed in nearly 30 min. Among the utilized zeolitic supports, zeolite 4A had the highest performance, but the mechanism of its synergetic effect on the activity of platinum nano catalyst was not found and requires more investigation.     

Palladium nanoclusters entrapped in polyurea: A recyclable and efficient catalyst for reduction of nitro-benzenes and hydrodechlorination of halogeno-benzenes

Polyurea-entrapped palladium nanoclusters have been prepared by interfacial polymerization in W/O emulsion and showed high thermal stability and chemical stability with the content of 0.12 mmol g^?1 Pd. This catalyst exhibited dual catalytic activity for reduction of nitro compounds and hydrodehalogenation of aromatic chlorides in atmospheric hydrogen with 100% yield for reduction of nitro compounds and >99% yield for hydrodehalogenation of aromatic chlorides. This immobilizing method was particularly effective and eliminated the need of special chelating groups.     

Studies of reactions of o-xylylene-α,α′-dihalides with palladium complexes and the catalytic synthesis of 3-isochromanone

Homogeneous catalysis by palladium complexes with phosphorus(III) ligands of the carbonylation of o-xylylene dihalides in the presence of water to form 3-isochromanone has been studied. Triphenylphosphine was found to provide the most effective catalyst, and by-products and intermediates of systems containing this ligand have been investigated. 2-Indanone is one by-product but is unstable to decomposition under catalytic conditions. Excess PPh₃ is necessary to prolong activity of the catalyst but is also transformed to bis-phosphonium compound [o-C₆H₄(CH₂PPh₃)₂]X₂ (X = Cl or Br); this quaternization has been investigated and the structure of the bromide salt determined by X-ray diffraction. An unstable oxidative addition product of Pd(PPh₃)₄ was detected as a probable intermediate and related to the previously reported but catalytically-inactive complex trans-Pd(o-CH₂C₆H₄CH₂Cl)Cl(PMe₃)₂, which has been structurally characterized by X-ray diffraction in this work.     

Perovskite-type ferromagnetic BiFeO3 nanopowder: a new magnetically recoverable heterogeneous nanocatalyst for efficient and selective transfer hydrogenation of aromatic nitro compounds into aromatic amines under microwave heating

Perovskite-type ferromagnetic BiFeO₃ nanopowder was readily synthesized via thermal decomposition of Bi[Fe(CN)₆]·5H₂O complex and characterized using thermal analysis (TGA/DSC), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT–IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), magnetic measurement and Brunauer–Emmett–Teller (BET) specific surface area measurements. The magnetic measurements show a ferromagnetic behavior for the BiFeO₃ nanoparticles at room temperature. This nanosized ferromagnetic oxide with an average particle size of approximately 20 nm and a specific surface area of 48.5 m²/g was used as a new magnetically recoverable heterogeneous nanocatalyst for the highly efficient and selective reduction of aromatic nitro compounds into their corresponding amines by using propan-2-ol as the hydrogen donor under microwave irradiation. This method is regio- and chemoselective, clean, inexpensive and compatible with the substrates having hydrogenlyzable or reducible functional groups. As compared with conventional heating, this method is very fast and suitable for the large-scale preparation of different substituted anilines as well as other arylamines. The catalyst can also be reused without loss of activity.     

Magnetically nano core–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Cu(OH)<Subscript>x</Subscript>: a highly efficient and reusable catalyst for rapid and green reduction of nitro compounds

Magnetically separable nano core–shell Fe₃O₄@Cu(OH)_x with 22 % Cu content was prepared by the addition of sodium hydroxide to a mixture of CuCl₂·2H₂O and nano Fe₃O₄ in water. Characterization of the impregnated copper hydroxide was carried out by X-ray fluorescence (XRF), X-ray diffraction (XRD) atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), value stream mapping (VSM) and Brunauer–Emmett–Teller (BET) analysis. The core–shell nanocatalyst exhibited the excellent catalytic activity toward reduction of various nitro compounds to the corresponding amines with NaBH₄. All reactions were carried out in H₂O (55–60 °C) within 3–15 min to afford amines in high to excellent yields. Reusability of core–shell Cu(OH)_x catalyst was examined 9 times without significant loss of its catalytic activity.     

Two new micro-isostructural metal–organic polymers based on mixed-ligand copper(I): Structures and selective sensing of nitro explosives in water

Two new one-dimensional metal–organic polymers (MOPs) {[Cu(L)(PPh₂Py)·I₂]·CH₃Cl}_n ( I ) and {[Cu(L)(PPh₂Py)·Br₂]·CH₃Cl}_n ( II ) (L = (1E,2E)-1,2-bis(pyridine-4-ylmethylene)hydrazine) (4-bpmh)) have been synthesized and elucidated by single crystal X-ray diffraction. The results of X-ray diffraction analysis unambiguously revealed that the two polymers are isostructural with the major intermolecular CH⋯π and π⋯π interactions. Microstructures of these polymers were also synthesized using a sonochemical method in different concentrations and reaction times. Field emission scanning electron microscopy, powder X-ray diffraction, thermogravimetric analysis and IR spectroscopy were applied to fully characterize these compounds. The photoluminescent properties of microrod MOPs were also evaluated to add to our understanding of their potential ability for nitro compound sensing. These experiments showed that MOPs I and II are good luminescence sensors for detection of nitro explosives in aqueous media. The probes maintained their high sensitivity and selectivity for 4-nitrophenol (4-NP). The energy transfer process accompanied by electrostatic interactions of 4-NP with these MOPs can be considered as an influential reason for the selectivity of 4-NP. The competitive study of the quenching process has a6lso shown superior operation with microparticles compared with bulky polymers. These results indicate that this method may be useful to synthesize luminescent materials possessing good sensing properties.     

Cyclopentadienyl-ruthenium(II) complexes as efficient catalysts for the reduction of carbonyl compounds

This work reports the reduction of a large variety of aldehydes and ketones with the system PhSiH₃/[CpRu(PPh₃)₂Cl] in good to excellent yields and high chemoselectivity. The catalyst [CpRu(PPh₃)₂Cl] can be used in at least 12 catalytic cycles with excellent catalytic activity and several substrates were reduced under solvent free conditions.     

Synthesis of recoverable palladium composite as an efficient catalyst for the reduction of nitroarene compounds and Suzuki cross-coupling reactions using sepiolite clay and magnetic nanoparticles (Fe3O4@sepiolite-Pd2+)

Clays are nontoxic, inexpensive, abundant, and have great potential as catalytic carriers because of their special structure, surface, and suitability for supporting transition metals. In this study, sepiolite was used as a ligand for the heterogenization of palladium chloride on Fe₃O₄ nanoparticle surface as a novel, high temperature stable, and recoverable green catalyst (Fe₃O₄@sepiolite-Pd²⁺). The catalytic activity of this system was tested in the reduction of nitroarene compounds and the Suzuki cross-coupling reaction. The catalyst structure was characterized using spectroscopic data and magnetic and thermal techniques such as Fourier transform infrared, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, vibrating sample magnetometer (VSM), and thermogravimetric analysis.     

Reaction of (PPh3)2C→CO2 with Halogenated Hydrocarbons; Formation and Crystal Structure of a Cationic Ester with 1, 2‐Dichloroethane

The carbodiphosphorane CO₂ adduct ( 2 ) reacts slowly with 1, 2‐dichloroethane to give (HC{PPh₃}₂)Cl ( 5 ) as result of HCl abstraction along with the ester‐like salt (ClCH₂CH₂O(O)CC{PPh₃}₂)Cl ( 4 ) from nucleophilic substitution of one Cl^– by 2 . Both compounds could be separated by fractional crystallization. Attempts to dissolve 2 in 1, 2‐difluorobenzene leads to small amounts of the hydrolysis product (HC{PPh₃}₂)(HCO₃) · H₂O ( 6· H₂O) caused by some humidity in the solvent. All compounds could be crystallized and the structures studied by X‐ray analyses and ³¹P NMR spectroscopy.     

Cu/活性炭催化剂：水合肼还原制备及催化甲醇氧化羰基化

以活性炭为载体,水合肼为还原剂制备了负载型Cu/活性炭催化剂,考察了水合肼/硝酸铜物质的量的比对催化甲醇气相氧化羰基化性能的影响,并采用XRD、XPS、H2-TPR和SEM等手段对催化剂进行了表征。结果表明,不加入还原剂水合肼时,催化剂中仅有CuO;随着水合肼/硝酸铜物质的量的比的增加,二价铜逐步被还原为Cu2O和/或单质Cu0,未被还原的Cu(OH)2在催化剂干燥过程中分解形成分散态CuO存在于催化剂表面。当水合肼/硝酸铜物质的量的比为0.75时,催化剂的催化性能最好,碳酸二甲酯的时空收率为120.62 mg.(g.h)-1,选择性为74.51%,甲醇转化率达到3.88%。在93 h反应时间内,催化剂都保持了较高的反应活性和选择性。此时铜物种以Cu2O和分散态CuO为主,Cu2O是主要的活性物种。     

Pd immobilized on thiol-modified magnetic nanoparticles: A complete magnetically recoverable and highly active catalyst for hydrogenation reactions

A palladium-based catalyst supported on thiol-modified superparamagnetic nanoparticles was successfully prepared by co-precipitation method. These magnetic nanomaterials were characterized by elemental analysis (EA), inductively coupled plasma (ICP), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fourier transform-infrared (FT-IR), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The conversions of various aromatic nitro and unsaturated compounds can receive a really high yield with the existence of magnetic nanomaterials. The turn-over frequency (TOF) can be 66.46 h⁻¹ in ethanol under a H₂ atmosphere at room temperature. In this paper, the conversions of aromatic nitro bearing a variety of substituents were 93.56–100%, moreover, the catalyst afforded over 90% yield in the reducing unsaturated compounds. Another advantage is that the magnetite nanoparticles modified by thiol group can be separated just through the external magnetic force and can be reused atleast ten times without any significant loss in activity.     

An active and recyclable bicontinuous cubic Ia3d mesostructural Rh(I) organometal catalyst for 1,4-conjugate addition reaction in aqueous medium

An active and reusable heterogeneous Rh(I) organometal catalyst (Rh(I)-PMO-3D) was synthesized by template-directed co-condensation of Rh[PPh₂(CH₂)₂Si(OCH₂CH₃)₃]₃Cl and (CH₃CH₂O)₃SiPhSi(OCH₂CH₃)₃. This catalyst displayed bicontinuous cubic Ia3d mesostructure channel, which ensured the high dispersion of Rh(I) active sites and the convenient diffusion of reactant molecules into the pore channels. Meanwhile, the Ph-functionalization could enhance the surface hydrophobicity, which promoted the adsorption of organic reactant molecules on the catalyst, especially in aqueous medium. During water-medium 1,4-conjugate addition reactions, Rh(I)-PMO-3D catalyst exhibits higher catalytic activity than the corresponding homogeneous Rh(I) catalyst and could be used repetitively for more than five times, showing a good potential in industrial applications.     

Synthesis and characterization of stable osmafuran starting from HC≡CCH(OH)C≡CH and OsHCl(CO)(PPh3)3

This paper presents a new convenient route to prepare osmafuran starting from readily accessible HC≡CCH(OH)C≡CH and OsHCl(CO)(PPh₃)₃. Treatment of a solution of OsHCl(CO)(PPh₃)₃ in dichloromethane with HC≡CCH(OH)C≡CH, followed by the addition of acetic acid, produced osmafuran [Os(CHC(PPh₃)CO(CH₂CH₃))Cl(CO)(PPh₃)₂]Cl (2). 2 has been isolated in good yield and fully characterized. ¹H and ¹³C NMR spectra show the characteristic downfield chemical shifts of the ring hydrogen and carbon atoms. NMR and X-ray diffraction data provide strong evidence for the aromatic nature of 2. Probably due to the effect of the phosphonium substituent, 2 exhibits remarkable thermal stability, air stability and lower reactivity.

     

制备方法对Co-MOR催化剂CH4选择还原NO性能的影响

采用离子交换法、浸渍法制备一系列的Co-MOR 催化剂, 并将其用于CH₄选择性催化还原 NO_x(CH₄-SCR)反应. 运用X 射线衍射(XRD)、X 射线荧光光谱(XRF)、扫描电子显微镜(SEM)、紫外-拉曼(UVRaman)光谱、X射线光电子能谱(XPS)、NO程序升温脱附(NO-TPD)等手段对催化剂进行了表征. 结果表明, 浸渍法制备的催化剂, Co以Co₃O₄形式存在; 而离子交换法制备的催化剂, Co以离子形式进入丝光沸石(MOR)骨架之中, 在催化剂上形成更多的Co²⁺和[Co-O-Co]²⁺, 形成更均匀NO吸附中心和CH₄-SCR反应活性中心. 催化剂活性评价表明离子交换法制备的催化剂具有更宽的活性温度区间, Co(0.30)-MOR 催化剂在327-450℃温度范围内NO转化率大于50%.     

Influence of the reaction parameters on the Pd—HCl catalysed synthesis of phenylacetic acid derivatives via reduction of mandelic acid derivatives with carbon monoxide

The catalytic system Pd/C—HCl is highly active in the reduction of mandelic acid derivatives to phenylacetic acid derivatives with carbon monoxide when the aromatic ring is para-substituted with a hydroxy group. Typical reaction conditions are: 70–110 °C, 20–100 atm of carbon monoxide, benzene—ethanol as reaction medium, substrate/Pd=10²–10⁴/1, HCl/substrate=0.3–0.8/1. [Pd] = 10⁻² −10⁻⁴ M. When the catalytic system is used in combination with PPh₃ a slightly higher activity is observed. Comparable results are observed when using a Pd(II) catalyst precursor such as PdX₂, in combination with PPh₃, or PdX₂(PPh₃)₂ (XCl, AcO). When operating at 110 °C, decomposition to metallic palladium occurs. Pd(II) complexes with diphosphine ligands, such as diphenylphosphinemethane, -ethane, -propane or -butane, do not show any catalytic activity and are recovered unchanged. These observations suggest that Pd(0) complexes play a key role in the catalytic cycle. The proposed catalytic cycle proceeds as follows: the chloride ArCHClCOOR, formed in situ upon reaction of ArCHOHCOOR with hydrochloric acid, oxidatively adds to a Pd(0) species with formation of a catalytic intermediate having a Pd—[CH(Ar)COOR] moiety, which inserts a CO molecule, yielding an acyl intermediate of the type Pd—[COCH(Ar)COOR]. The nucleophilic attack of H₂O on the carbon atom of the carbonyl ligand gives back the Pd(0) complex to the catalytic cycle and yields a phenylmalonic acid derivative, which produces the final product, ArCH₂COOR, upon CO₂ evolution. Alternatively, protonolysis of the intermediate having a Pd—[CH(Ar)COOR] moiety yields directly the final product and a Pd(II) species, which is then reduced by CO to Pd(0). Moreover, no catalytic activity is observed when the Pd/C—HCl system is used in combination with any one of the above diphosphine ligands, probably because these ligands block the sites on the catalyst able to promote the catalytic cycle or because they prevent the reduction of Pd(II) to Pd(0). The influence of the following reaction parameters has been studied: concentration of HCl, PPh₃, palladium and substrate, pressure of carbon monoxide, the temperature, reaction time and solvent. The results are compared with those obtained in the carbonylation of aromatic aldehydes to phenylacetic acid derivatives catalyzed by the same system, for which it has been proposed that the catalysis occurs via carbonylation of the aldehyde to a mandelic acid derivative as an intermediate, which is further reduced with CO to yield the final product.     

Synthesis of γ-keto carboxylic acids from γ-keto-α-chloro carboxylic acids via carbonylation—decarboxylation reactions catalysed by a palladium system

A palladium-based catalytic system is highly active in the synthesis of γ-keto acids of type ArCOCH₂CH₂COOH via carbonylation-decarboxylation of the corresponding α-chloride. Typical reaction conditions are: P(CO) = 20–30 atm; substrate/H₂O/Pd = 100–400/800–1000/1 (mol); temperature: 100–110 °C; [Pd]=0.25 × 10⁻²−1 × 1O⁻² M; solvent: acetone; reaction time: 1–2 h. A palladium(II) complex can be used as catalyst precursor. Under the reaction conditions above, reduction of the precursor to palladium metal occurs to a variable extent. High catalytic activity is observed when the precursor undergoes extensive decomposition to the metal. Pd/C is also highly active. Slightly higher yields are obtainable when the catalytic system is used in combination with a ligand such as PPh₃. A mechanism for the catalytic cycle is proposed: (i) The starting keto chloride undergoes oxidative addition to reduced palladium with formation of a catalytic intermediate having a Pd-[CH(COOH)CH₂COPh] moiety. The reduced palladium may be the metal coordinated by other atoms of palladium and/or by carbon monoxide and/or by a PPh₃ ligand when catalysis is carried out in the presence of this ligand. It is also proposed that the keto group in the β-position with respect to the carbon atom bonded to chlorine weakens the CCl bond, easing the oxidative addition step and enhancing the activity of the catalyst. (ii) Carbon monoxide ‘inserts’ into the PdC bond of the above intermediate to give an acyl catalytic intermediate having a Pd-[COCH(COOH)CH₂COPh] moiety. (iii) Nucleophilic attack of H₂O to the carbon atom of the carbonyl group bonded to the metal of the acyl intermediate yields a malonic acid derivative as product intermediate. This, upon decarboxylation, gives the final product. Alternatively, the desired product may form without the malonic acid derivative intermediate, through the following reaction pathway: the acyl intermediate undergoes decarboxylation with formation of a different acyl intermediate, having a Pd-[CO-CH₂CH₂COPh] moiety, which, upon nucleophilic attack of H₂O on the carbon atom of the carbonyl group bonded to the metal, yields the final product.     

Keplerate巨型纳米多孔聚氧钼酸盐作为可重复使用催化剂用于合成1,2,4,5-四取代咪唑(英文)

The Keplerate‐type giant nanoporous isopolyoxomolybdate (NH4)42[MoVI72MoV60O372‐(CH3COO)30(H2O)72], denoted {Mo132}, has been used as a catalyst for the synthesis of1,2,4,5‐tetrasubstituted imidazoles by the one‐pot, four‐component thermal reaction of benzil with aromatic aldehydes, primary amines, and ammonium acetate under solvent‐free conditions. The catalyst was prepared according to a previously published literature procedure using inexpensive and readily available starting materials, and subsequently characterized by FT‐IR, UV and X‐ray diffraction spectroscopy, as well as microanalysis. The results showed that {Mo132} exhibited high catalytic activity towards the synthesis of 1,2,4,5‐tetrasubstituted imidazoles, with the desired products being formed in good to high yields. Furthermore, the catalyst was recyclable and could be reused at least three times without any discernible loss in its catalytic activity. Overall, this new catalytic method for the synthesis of 1,2,4,5‐tetrasubstituted imidazoles provides rapid access to the desired compounds following a simple work‐up procedure, and avoids the use of harmful organic solvents. This method therefore represents a significant improvement over the methods currently available for the synthesis of tetrasubstituted imidazoles.     

Die Chlorooxoarsenate(III) (PPh4)2[As4O2Cl10] · 2 CH3CN und (PPh4)2[As2OCl6] · 3 CH3CN

The Chlorooxoarsenates(III) (PPh₄)₂[As₄O₂Cl₁₀] · 2 CH₃CN and (PPh₄)₂[As₂OCl₆] · 3 CH₃CN (PPh₄)₂[As₂Cl₈] can be prepared from As₂O₃, SOCl₂ and PPh₄Cl in acetonitrile. Its oxidation with chlorine yields PPh₄[AsCl₆]. This was also obtained directly from arsenic, chlorine and PPh₄Cl, (PPh₄)₂[As₄O₂Cl₁₀] · 2 CH₃CN being a side product; the latter was obtained with high yield from AsCl₃, As₂O₃ and PPh₄Cl in acetonitrile. By addition of PPh₄Cl it was converted to (PPh₄)₂[As₂OCl₆] · 3 CH₃CN. According to their X-ray crystal structure analyses, both crystallize in the triclinic space group P 1. The [As₄O₂Cl₁₀]^2– ion can be regarded as a centrosymmetric association product of two Cl₂AsOAsCl₂ molecules and two Cl^– ions, each Cl^– ion being coordinated with all four As atoms. In the [As₂OCl₆]^2– ion the As atoms are linked via the O atom and two Cl atoms.     

P-C Bond Cleavage in Platinum Complexes Containing bis (Diphenylphosphino) Methane Promoted with a Phase-Transfer Catalyst

With a phase-transfer catalyst, Pt-dppm (dppm = Ph₂PCH₂PPh₂) complexes undergo basic hydrolysis, in which a dppm ligand is hydrolyzed to produce PPh₂Me and PPh₂OH (or PPh₂O). The ease of this hydrolysis reaction depends partly on the molecular charges of the metal complexes. Hydrolysis of neutral [Pt(dppm)(L-L)] (L-L = S₂CO², S₂P(O)(OEt)^2? and mnt = S₂C₂(CN)₂^2?) is slower than that of monocationic [Pt(dppm)(L′-L′)]Cl (L′-V = S₂CNEt₂-, (CH₂)₂S(O)Me and acetylacetonate) compounds. Among the neutral compounds, hydrolysis of [Pt(dppm)(mnt)] is more rapid than that of the other two. These results are rationalized according to the ease with which partial positive charges are induced on the dppm phosphorus atoms. The steric effect due to ligands trans to dppm also influences the rate of hydrolysis of Pt-dppm compounds. When trans ligands are Ph₂P(CH)₂PPh₂, Ph₂P(CH₂)₃PPh₂ and (Ph₂PO₂)H, no hydrolysis of dppm occurs. Hydrolysis of Pt-dppm compounds depends further on the concentrations of both the phase-transfer catalyst and OH^? ions. All these results are consistent with nucleophilic attack of OH^? on dppm phosphorus atoms to release strain in the Pt-dppm ring.