Magnetically recoverable γ-Fe2O3 nanoparticles as a highly active catalyst for Friedel–Crafts benzoylation reaction under ultrasound irradiation

A simple, facile and efficient method has been developed for the Friedel–Crafts benzoylation of arenes using magnetic γ-Fe₂O₃ nanoparticles under solvent-free sonication. The γ-Fe₂O₃ nanoparticles were used as an efficient and magnetically recoverable catalyst for the synthesis of aromatic ketones in good to excellent yields at room temperature under solvent-free. The reaction occurred with high regioselectivity under mild condition. The magnetic γ-Fe₂O₃ nanoparticles are economically synthesized in large-scale, easily separated from the reaction mixture by an external magnet and able to be reused several times without significant loss of the catalytic performance, which make them easy application to industrial processes.     

Catechol derivatives-coated Fe3O4 and γ-Fe2O3 nanoparticles as potential MRI contrast agents

Superparamagnetic iron oxide nanoparticles, Fe₃O₄ and γ-Fe₂O₃, were produced by the so-called polyol process. In order to stabilize the particles in a physiological environment as potential contrast agents for Magnetic Resonance Imaging (MRI), the as-prepared particles were successfully transferred to an aqueous medium through ligand exchange chemistry of the adsorbed polyol species with the dopamine or the catechaldehyde. The ligands were able to participate in bidentate binding to the nanoparticles surface and to improve the stability of aqueous suspensions of the nanoparticles. Analysis was performed by various techniques including X-ray diffraction, transmission electron microscopy, infrared spectroscopy and thermal analysis. The results of magnetic measurements and initial in vitro magnetic resonance imaging essays are presented for the pre- and post-surface modified nanoparticles, respectively and discussed in relation with their structure and microstructure.     

Facile synthesis of Fe3O4 nanoparticles by reduction phase transformation from γ-Fe2O3 nanoparticles in organic solvent

A phase transformation induced by the reduction of as-synthesized γ-maghemite (γ-Fe₂O₃) nanoparticles was performed in solution by exploiting the reservoir of reduction gas (CO) generated from the incomplete combustion reaction of organic substances in the reactor. Results from X-ray diffraction, color indicator, and magnetic analysis using a SQUID strongly support this phase transformation. Based on this route, monodisperse magnetite (Fe₃O₄) nanoparticles were simply produced in the range from 260 to 300 °C. Almost all aspects of the original γ-Fe₂O₃ nanoparticles, such as shape, size, and monodispersity, were maintained in the produced Fe₃O₄ nanoparticles.     

Role of surface spins on magnetization of Cr2O3 coated γ-Fe2O3 nanoparticles

Effect of surface spins in chromium oxide (Cr₂O₃) coated maghemite (γ-Fe₂O₃) nanoparticles (13 nm) as prepared by microwave plasma technique have been studied in detail. The temperature dependent zero field cooled/field cooled (ZFC/FC) measurements revealed the blocking temperature at T_B = 75 K. Simulated ZFC/FC curves exhibited large value of effective anisotropy of Cr₂O₃ coated γ-Fe₂O₃ nanoparticles as compared to bulk γ-Fe₂O₃ but less than bare γ-Fe₂O₃ nanoparticles. Bloch's law was fitted on M_S-T data and revealed the values of Bloch's constant B = 3.523 × 10⁻⁴ K^−b and Bloch's exponent b = 1.10. The higher value of B than in bulk is due to weaker exchange coupling J (B ̴ 1/J) on the surface of nanoparticle due to disorder surface spins, while lower value of b is due to no spin wave excitation in presence of large energy band gap at nanoscale. Kneller's law fit on H_C-T data deviated in all temperature range which is due to strong surface anisotropy, core-shell interactions and superparamagnetism. Interparticle interactions and spin glass behavior were investigated by using different physical laws for f-dependent ac susceptibility and they confirmed the presence of spin glass behavior which is due to disordered frozen surface spins and random interparticle interactions.     

N-Picolinamides as ligands in Ullman type C–O coupling reactions

Copper-catalyzed modified Ullmann coupling reactions creating C–O bonds, including diaryl ethers or phenols, are vital to organic synthesis. Synthesized N-phenyl-2-pyridinecarboxamide and its derivatives were used as ligands in conjunction with catalytic copper sources in the formation of various diaryl ethers and phenols. Various aryl and heteroaryl halides with electron donating and withdrawing groups were reacted with various phenols under mild reaction conditions providing moderate to excellent yields.     

Microstructural behavior of γ-Fe2O3 formation in reactions between layered iron oxychloride and sodium n-pentoxide

Microstructural behavior of γ-Fe₂O₃ formation in reactions between FeOCl and n-C₅H₁₁ONa was thoroughly investigated. Reactions were conducted at 50–150 °C for 3 days in an autoclave using n-C₅H₁₁OH as a solvent. X-ray diffraction (XRD) patterns and infrared (IR) spectra of the products suggested the crystallization of γ-Fe₂O₃ besides the formation of n-pentoxy derivatives of FeOCl. Scanning electron microscopic observation revealed that the FeOCl particles were divided into thin sheets upon reaction. The selected area electron diffractions (SAED) of the sheets revealed the crystallization of γ-Fe₂O₃ at even 80 °C, apparently due to the fact that the γ-Fe₂O₃ crystallization process involved a collapse from n-pentoxide derivatives with large separations between two adjacent layers. In the reaction at 150 °C, a part of the sheets was converted into highly oriented polycrystalline γ-Fe₂O₃ in improved crystallinity, and the SAED clearly showed that an oriented transformation with a crystallographic relationship of FeOCl (010)//γ-Fe₂O₃ (110) occurred. The reaction at 120 °C, on the contrary, led to the formation of randomly oriented γ-Fe₂O₃ crystallites within a sheet.     

Pd-isatin Schiff base complex immobilized onγ-Fe2O3 as a magnetically recyclable catalyst for the Heck and Suzuki cross-coupling reactions

A Pd‐isatin Schiff base complex immobilized onγ‐Fe2O3 (Pd‐isatin Schiff base‐γ‐Fe2O3) was synthe‐sized and characterized by Fourier transform infrared, scanning electron microscopy, high resolu‐tion tr...     

Bimetallic Co–Pd alloy nanoparticles as magnetically recoverable catalysts for the aerobic oxidation of alcohols in water

Co–Pd bimetallic alloy nanoparticle catalysts were prepared from CoCl₂, Pd(OAc)₂ and several capping agents with Li(C₂H₅)₃BH. The nanoparticle catalysts were applied to the aerobic oxidation of a variety of alcohols in water to give the corresponding carbonyl products. The catalyst was magnetically recovered and reused for further oxidation. The nanoparticle catalysts were characterized with TEM, ICP, and XPS analyses.     

Heterogeneous bimetallic Au–Co nanoparticles as new efficient catalysts for the three-component coupling reactions of amines,alkynes and CH2Cl2

Research on Chemical Intermediates - Propargylamines are key intermediates for the synthesis of many biologically active molecules. A new synthesis of propargylamines via a three component-coupling...     

Synthesis,characterization and magnetic properties of γ-Fe2O3 nanoparticles via a non-aqueous medium

Acicular shaped γ-Fe₂O₃ nanoparticles (major axis: 17±2 nm; minor axis: 1.7±1 nm) have been prepared using lauric acid as a non-aqueous medium. The products were investigated by IR, TG-DTA, XRD, Raman, SEM, TEM and magnetization measurements. For the preparation of pure γ-Fe₂O₃ nanoparticles, the suitable condition of the molar ratio of lauric acid to iron nitrate is set 2:1 and the appropriate temperature lies in the range 573–673 K. Besides, either pure α-Fe₂O₃ or a mixture of γ-Fe₂O₃ and α-Fe₂O₃ can also be obtained with the change of the molar ratio of lauric acid to iron nitrate. The experimental results indicate that the particle sizes, thermal stability and magnetic properties of the iron oxide strongly depend on the conditions in the preparation.     

Fe3O4@SiO2-polymer-imid-Pd magnetic porous nanosphere as magnetically separable catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling reactions

The activity of palladium nanoparticles supported on poly (N-vinylpyrrolidone) grafted Fe₃O₄@SiO₂ was investigated in the cross-coupling reactions. We have applied this catalyst under low loading of the supported palladium nanoparticles for the coupling of aryl halides with alkenes (Mizoroki–Heck reaction) and organoboronic acids (Suzuki–Miyaura reaction) in the absence of phosphorous ligands. Short reaction times and excellent yields of the products express the effectiveness of this catalyst. The nanocatalyst can be separated from the reaction mixture by applying a permanent magnet externally and can be reused for six times without appreciable change in catalytic activity. Also, the amount of leaching of Pd nanoparticles has been determined by ICP analysis and results showed low leaching of the metal into solution from the supported catalyst.     

Thin films of ��-Fe2O3 nanoparticles using as nonmetallic SERS-active nanosensors for submicromolar detection

A new kind of nonmetallic nanosensors based on surface-enhanced Raman spectroscopy (SERS) have been successfully prepared by the assembly of α-Fe₂O₃ nanoparticles (NPs) onto clean quartz surface via the cross-linker of hexamethylene diisocyanate (HDI). The resultant substrates have been characterized by electron micrographs, which show that the α-Fe₂O₃ NPs distribute on the modified surface uniformly with a monolayer or sub-monolayer structure. 4-mercaptopyridine (4-Mpy) and 2-mercaptobenzothiazole (2-MBT) molecules have been used as SERS probes to estimate the detection efficiency of the α-Fe₂O₃ thin films. The SERS experiments show that it is possible to record high quality SERS spectra from probe molecules on the α-Fe₂O₃ thin films at sub-micromolar ( < 10⁻⁶ mol/L) concentration. These results indicate that the highly ordered, uniformly roughed, highly sensitive and low-cost α-Fe₂O₃ thin films are excellent candidates for nonmetallic SERS-active nanosensors.     

Surface reactions of dimethyl ether on γ-Al2O3

The surface reactions of dimethyl ether (DME) on industrial alumina (γ-Al₂O₃) were studied by chromatographic analysis of the products at the outlet of the flow reactor and (independently) by diffuse reflectance IR spectroscopy. The major products of the reactions at 250°С were found to be methanol formed in the reaction of DME with hydroxyl groups (the 3720 and 3674 cm^–1 bands in the diffuse reflectance spectrum) and various methoxy groups (the 1121, 1070, 695, and 670 cm^–1 bands in the differential spectra). The presence of molecularly adsorbed methanol was confirmed by experiments with methanol fed in a high-temperature IR cell. The interaction of the resulting methanol molecule with the hydroxyl group led to the formation of a water molecule in the gas phase and a methoxy group on the oxide surface. Strong adsorption of molecular DME was revealed, which was favored by an increase in the temperature of the preliminary calcination of oxide from 250 to 450–500°С; treatment of alumina with water vapor after its preliminary contact with DME led to a recovery of the hydroxyl coating and a replacement of molecularly adsorbed DME with hydroxyl. The thermal effect recorded in a flow reactor was positive during the adsorption of DME and negative during the desorption of weakly bonded DME. Schemes of formation of methoxy groups in the interaction of DME and methanol with surface hydroxyls were suggested.     

Catalytic conversions of chloroolefines over iron oxide nanoparticles 3. Electronic and magnetic properties of γ-Fe2O3 nanoparticles immobilized on different silicas

Catalytic properties of superparamagnetic γ-ferric oxide nanoclusters, which are uniform in terms of size and magnetic properties were studied. The catalysts were supported on the activated silica gel matrix (AGM) prepared from the KSK-2 silica gel of globular structure and on the activated silica matrix (ASM) prepared from layered natural vermiculite. The clusters are active in some reactions of chloroolefin conversions: isomerization of dichlorobutenes and alkylation of benzene with allyl chloride. Their activity in these reactions is many times higher that of usual supported catalysts based on α-ferric oxide. Analysis of the Mössbauer spectra of the 2.5 wt.% Fe/AGM and 2.5 wt.%Fe/ASM samples before and after the reaction at T = 3–300 K shows that during the reaction some Fe^III ions arranged in ～2–3-nm γ-Fe₂O₃ nanoclusters magnetically ordered at 6 K are reduced to form a high-spin Fe^II complex in the paramagnetic state. According to the macroscopic magnetization data (SQUID) of the initial clusters, curves with hysteresis are observed at 2 K in the plots of forward and backward magnetization, while the 2.5 wt.%Fe/ASM catalyst after the reaction at T = 2 K demonstrates a linear field dependence of the magnetization passing through the coordinate origin. Analysis of the Mössbauer spectra and magnetic properties suggests that during the catalytic reaction the Fe^III ions in the γ-Fe₂O₃ nanoclusters interact with chloroolefin with the allylic structure to be partially reduced to the Fe^II ions that are bound in a complex containing chloride ions and O^II ion(s) of the silicate matrix as ligands. This is a reason, probably, for the high catalytic activity of γ-Fe₂O₃ nanoparticles.     

Thermal properties of the γ-Fe2O3/poly(methyl methacrylate) core/shell nanoparticles

Thermal properties of γ-Fe₂O₃/poly(methyl methacrylate) (PMMA) core/shell particles with an average core size of 4 nm were studied through measurements of thermogravimetry, powder X-ray diffraction and magnetization. The thermal degradation of the PMMA shell in the air was found to occur at temperatures lower by about 60 °C than that of free PMMA. Random scission of the PMMA chains seemed to be catalyzed by the core oxide. The γ-Fe₂O₃ to α-Fe₂O₃ structural transformation took place at different temperatures depending upon the shell material. Namely, α-Fe₂O₃ was the only product for the caprylate-capped γ-Fe₂O₃ nanoparticles treated at 400 °C, whereas γ-Fe₂O₃ still remained for the γ-Fe₂O₃/PMMA composite treated at 500 °C. It is possible that some species containing silicon of the polymerization initiator origin were formed on the surface and prevented interparticle atomic diffusions needed for the γ–α transformation.     

Catalytic applications of an organosuperbase dendron grafted on mesoporous SBA-15 and a related palladium complex in Henry and Suzuki–Miyaura coupling reactions

An efficient synthetic method for the synthesis of a basic amine dendron grafted on SBA-15 and a related Pd(II) complex as two novel catalysts has been developed. The prepared catalysts were evaluated in Henry and Suzuki–Miyaura coupling reactions and were found to exhibit excellent heterogeneous catalytic activity in green media, and could be easily separated and reused several times.     

Preparation of monodispersed ��-Fe2O3 nanoparticles by a hydrothermal synthetic route

Monodispersed ??-Fe₂O₃ nanoparticles modified by sodium dodecylbenzene sulfonate (SDBS) surfactant and assisted by glycerol have been successfully synthesized via a hydrothermal process using FeCl₃·6H₂O as the starting precursor. These nanoparticles possess good crystallinity and have an average particle size of 100 nm. The as-prepared products are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and a superconducting quantum interference device magnetometer. SDBS and glycerol played an important role in controlling the final morphology of the products. Magnetic hysteresis measurements reveal that monodispersed ??-Fe₂O₃ nanoparticles exhibit normal ferromagnetic behaviors with the remanent magnetization and coercivity of 0.2389 emu/g and 2339.0 Oe at room temperature.     

Synthesis and magnetic properties of the γ-Fe2O3/poly-(methyl methacrylate)-core/shell nanoparticles

The synthesis of γ-Fe₂O₃/poly-(methyl methacrylate)-core/shell nanoparticles and their magnetic properties are reported. Specific γ-Fe₂O₃ nanoparticles capable of initiating atom transfer radical polymerization (ATRP) were prepared by a ligand exchange reaction of ((chloromethyl)phenylethyl)-dimethylchlorosilane and caprylate-capped γ-Fe₂O₃ nanoparticles of 4 nm in diameter, and the ATRP of methyl methacrylate was carried out subsequently. These nanoparticles were characterized with Fourier transform infrared spectroscopy, transmission electron microscopy and Mössbauer spectroscopy. Low temperature magnetic properties investigated with SQUID magnetometry revealed that the coercivity and the blocking temperature changed slightly owing to surface effects.     

Direct assembly of polyarenes via C-C coupling Using PIFA/BF3·Et2O

Direct oxidative Kita-type coupling between naphthalene and substituted benzenes was found to proceed via four-component coupling, leading to a linear tetraarene with a binaphthalene core. The methodology was extendable to the coupling of unfunctionalized 1,1'-binaphthalene with mesitylene to give a linear hexaarene product in a remarkably chemoselective manner in 87% yield. The method represents an attractive alternative to the traditional syntheses of related oligonaphthalene products via a sequence of metal-catalyzed cross-coupling steps.