A theoretical study of the dissociative chemisorption of hydrogen on carbon nanotubes

Potential profiles were obtained for the chemisorption of hydrogen on (n, n) and (n, 0) carbon nanotubes. The energy barriers and rate constants for hydrogen molecule sorption on and desorption from various nanotubes were determined. The constants for sorption and desorption were used to calculate sorption-desorption equilibrium constants. Sorption on outside nanotube surfaces was found to be more favorable energetically than sorption on inside surfaces.     

Catalytic properties of monomeric and oligomeric Cu(II) phenylhydrazono imine chelates immobilized on zeolite with a topological anchor

Heterogeneous catalysts for liquid-phase oxidation of cyclohexene with molecular oxygen were prepared by topological-anchor immobilization on CaA zeolite of a monomeric Cu(II) chelate with N,N′-trimethylenebis(2-methyl-1-benzoylglyoxal 1-phenylhydrazone 2-imine) and of an oligomeric product of its condensation with ethylenediamine. The samples prepared contain surface monomeric and oligomeric Cu(II) chelates oriented toward the reaction medium, which makes them accessible to reactant molecules. The catalytic properties of the above monomeric chelate are preserved in going to the oligomers. The apparent rate constants per metal center for both homogeneous (soluble monomeric chelate) and heterogeneous modes coincide, suggesting the pseudohomogeneous behavior of the supported samples. The topological-anchor immobilization of insoluble oligomeric Cu(II) polychelates on zeolite leads to their more efficient utilization as heterogeneous catalysts and can be considered as one of examples of combining advantages of homogeneous and heterogeneous catalysis.     

Advances in liquid-phase Friedel-Crafts acylation of aromatics catalyzed by heterogeneous solids

In the last few decades, significant improvements toward the development of environmentally benign processes have been achieved in the liquid-phase Friedel-Crafts acylation reactions. Many efforts have been devoted to the research on solid catalysts adequate to substitute homogeneous protonic acids or Lewis acids as traditionally employed catalysts in the acid-catalyzed Friedel-Crafts acylation processes. This short article describes the recent developments on catalysis by gallium (Ga), indium (In) and thallium (Tl) based novel heterogeneous solids for the liquid-phase Friedel-Crafts acylation of aromatics by acyl halide. The above heterogeneous catalysts are efficient for Friedel-Crafts acylation reaction and exhibited superior activity than the traditionally employed strongly acidic solid catalysts. Unlike conventional acidic catalyst, the acylation activity of Ga, In and Tl based solids, additionally having redox functions, does not depend solely on their acidic properties, even present. These solids in their non-acidic or basic form also show high acylation activity. Based on the catalytic results over these novel solids a plausible reaction mechanism for the acylation is proposed.Dedicated to Professor Seitaro Namba on the occasion of his 64th birthday.     

Friedel-Crafts catalytic alkylations using rare earth-based mineral supports

Rare earth halides supported on mineral supports (K10 montmorillonite and silica) were investigated as catalysts for Friedel-Crafts alkylations. This project concerns the replacement of the widely used Lewis acid AlCl₃ in Friedel-Crafts reactions by environmentally friendly catalysts in that they circumvent the production of aluminum waste. The catalytic activity of these heterogeneous catalysts was established in a series of alkylations of aromatic compounds.     

One-step preparation of α-chlorostyrenes

α-Chlorostyrenes were prepared via a one-step method involving Friedel-Crafts reaction of various aromatic substrates with acid chlorides in the presence of a heterogeneous Si-Fe catalyst.     

Trost氮杂半冠醚手性配体在不对称催化反应中的应用

双功能手性金属络合物催化的不对称反应是目前有机化学研究的热点之一。本文综述了氮杂半冠醚手性配体与金属有机试剂络合的双金属催化剂,在催化不对称aldol反应、不对称Henry反应、不对称Michael反应、不对称Mannich反应、不对称Friedel-Crafts烷基化反应、不对称炔基化反应、不对称硅氰化反应、共聚反应、去对称化反应以及不对称Nozaki-Hiyama烯丙基化反应体系中的应用进展,重点介绍了不同催化体系对催化剂和反应底物之间立体效应和电子效应的影响,总结了控制反应立体选择性的规律以及有关催化反应的机理。     

Metal-catalyzed hydroxylaminolysis of unactivated amide and peptide bonds

Kinetics of the hydroxylaminolysis of acetamide, glycinamide, glycylglycine and triglycine have been studied in the range of temperatures 37-60 degrees C as a function of pH and hydroxylamine concentration. Rate constants for specific acid, general-acid and general-base catalyzed pathways have been determined for all substrates (for glycine derivatives rate constants for different protonation forms were obtained). Testing different metal ions as possible reaction catalysts revealed a significant catalytic effect of Zn(II) on the hydroxylaminolysis of glycine substrates, but not acetamide. On the basis of the kinetic results, a mechanism of Zn(II) catalysis is proposed, which involves the coordination of the metal ion to the alpha-amino group of the substrate and the base-assisted nucleophilic attack of hydroxylamine on the bound substrate. The product analysis by proton NMR shows that the primary reaction product in the catalytic reaction is glycine hydroxamic acid, which undergoes further Zn(II)-catalyzed hydrolysis to glycine. Thus the final result of the Zn(II)-catalyzed treatment of peptides by hydroxylamine is hydrolytic cleavage.     

Reaction Mechanisms and Kinetics of the Melt Transesterification of Bisphenol‐A and Diphenyl Carbonate

The catalyzed and uncatalyzed reaction mechanisms of the melt transesterification process of bisphenol‐A and diphenyl carbonate are proposed based on nucleophilic substitution at the carbonyl group of the reactants. The reaction paths and energy barriers of the melt transesterification reaction were predicted and identified via density functional theory (DFT) calculations. The calculations reveal that the different oligomers with only one repeating unit are formed through different thermal processes. The theoretical evaluation further indicates that the basic hydroxide catalysts can reduce the energy barrier for the transesterification reaction, which allows subsequent nucleophilic attack to easily occur. Furthermore, the reaction kinetics of transesterification using tetraethyl ammonium hydroxide as a catalyst were investigated experimentally over a temperature range of 155–175°C. The reaction rate constants and equilibrium constants were determined based on the functional group model, and the equilibrium constants decreased with increasing reaction temperature. A detailed molecular species model with a specific repeating unit (n = 3) was developed and applied to predict the change in the reactants, oligomers, and phenol, and the experimental data and model calculation agree quite well. The standard curves of the oligomer were reversely derived, which provide intuitive insight into the concentration change of each oligomer. Both the DFT calculations and experimental results indicate that the C1 oligomer is first formed, and some of which are then converted to other types or higher molecular weight oligomers.     

The sorption properties of rutile and its catalytic activity in the destruction of dyes

The photocatalytic destruction of cationic and anionic dyes on dispersed spectrally pure rutile in the presence of oxygen was studied. The rate constant for these reactions does not correlate with the rate constant for the photobleaching of these dyes in homogeneous solutions in the absence of a catalyst, the rate constants for adsorption, and the rate of establishment of sorption equilibrium in rutile-dye systems, but increases as the sorption value grows. The photocatalytic process substantially disturbs sorption equilibrium in most of the systems studied. The conclusion is drawn that both weakly and strongly sorbed substrate molecules can participate in the photocatalytic process.     

甲醇POSR制氢的反应网络热力学分析和有效因子的估算

在Cu/ZnO/Al2O3催化剂上对甲醇部分氧化蒸汽重整制备氢气反应的动力学过程进行了研究。在常压和473 K～1 073 K温度范围内对该反应网络中的甲醇部分氧化、甲醇蒸汽重整、甲醇分解和水煤气反应的化学平衡进行了分析。在对这些反应的催化剂Cu/ZnO/Al2O3动力学研究的基础上，根据有效因子的基本概念，考虑催化剂颗粒内的扩散限制，对每个反应沿反应器床层的有效因子进行了估算。     

The reaction of N-tosyl imines with heteroaromatic compounds: a new access to triheteroarylmethanes

Useful triheteroarylmethanes were prepared by the double Friedel-Crafts reaction of a wide variety of aromatic N-tosyl imines with furan, thiophene, and pyrrole in the presence of Cu(OTf)₂ and Montmorillonite K-10 clay catalysts.     

Determination of equilibrium constants and computational interaction energies for adducts of [Rh2(RCO2)(4-n)(PC)n] (n = 0-2) with Lewis bases

Properties of dirhodium catalysts with cyclometalated aryl phosphine ligands have been studied. We report here the study of the acid-base reaction of Rh2(RCO2)2(PC)2(H2O)2 catalysts (PC = cyclometalated aryl phosphine) with different Lewis bases. The determination of the equilibrium constants of these reactions can be used to study to which extent the properties of the axial coordination site of the catalyst, considered the active site, are affected by modification of the metalated phosphines, the carboxylate ligands, or the incoming axial ligand. The trends in the computational density functional theory interaction energies show good agreement with the major trends in the equilibrium constants, thus enabling a further study of the influence of the modification of the ligand core.     

Monte Carlo simulation of complex isomerization, II. Effect of adsorption on product selectivity

The complex isomerization A=B=C over zeolite catalysts was simulated by the Monte Carlo method, and the effect of adsorption of molecules accompanied with chemical reaction upon the product selectivity has been investigated. The results show that the product selectivity is clearly related to the difference of equilibrium adsorption constants of molecules in the reaction. This suggests that the shape selectivity in zeolite-catalyzed reactions is the result of the channel structure and surface acidity of zeolite catalysts.     

Sorption interactions of volatile organic compounds with organoclays under different humidities by using linear solvation energy relationships

Organoclays are usually used as sorbents to reduce the spread of organic compounds and to remove them at contaminated sites. The sorption equilibrium and the mechanisms of volatile organic compounds (VOCs) on organoclays under different humidities are helpful for developing efficient organoclays and for predicting the fate of VOCs in the environment. In this study, the organoclay was synthesized through exchanging inorganic cations by hexadecyltrimethyl ammonium (HDTMA) into montmorillonite, resulting in 12?% of organic content. The surface area of organoclay was smaller than the unmodified clay due to the incorporation of organic cations into the interlayer. Both adsorption on organoclay surface and partition into the incorporated HDTMA in organoclay played roles on the sorption process. Compared the sorption coefficients in montmorillonite and different modified clays, the incorporated organic cations overcame the inhibition effect of hydrophilic surface of clay on the sorption process of hydrophobic organic compounds from water. The sorption coefficients of VOC vapors on organoclay were further characterized using a linear solvation energy relationship (LSER). The fitted LSER equations were obtained by a multiple regression of the sorption coefficients of 22 probe chemicals against their solvation parameters. The coefficients of the five-parameter LSER equations showed that high HDTMA-content montmorillonite interacts with VOC molecules mainly through dispersion, partly through dipolarity/polarizability and hydrogen-bonds as well as with negative π-/n-electron pair interaction. The interaction analysis by LSERs suggests that the potential predominant factors governing the sorption of VOCs are dispersion interactions under all tested humidity conditions, similar with the lower level modified clay. The derived LSER equations successfully fit the sorption coefficients of VOCs on organoclay under different humidity conditions. It is helpful to design better toxic vapor removal strategy and evaluate the fate of organic contaminants in the environment.     

Ion exchange properties of crystalline bismuth molybdenum hydrous oxide and its intercalates: Equilibrium and kinetics of UO 2 2+ ions on the crystals

The sorption of uranyl ions on crystalline bismuth molybdenum hydrous oxide and its intercalates were investigated from point of view of both equilibrium and kinetics. Ion exchange isotherms of uranyl ions on the crystals were obtained, and ionic sieve effect was employed to describe the characteristics of ion exchange isotherms. The best fitting for sorption of uranyl ions on BMHO was achieved by means of the Langmuir isotherm, while the Freundlich isotherm appeared to best fit for its intercalates. The slightly negative free-energy change indicates that, thermodynamically, the crystals behave less favourable for uranyl ions. The equation derived from S_N2 chemical reactions was proved to fit the rate curves, and the rate constants were determined. The comparison between the calculated and observed pH values as a function of time further verified the chemical reaction mechanism.     

Synthesis and Catalytic Activity of Atrane-type Hard and Soft Lewis Superacids with a Silyl,Germyl, or Stannyl Cationic Center

The synthesis and isolation of atrane-type molecules 1 E⁺ (E=Si, Ge, or Sn) having a cationic group 14 elemental center are reported. The cations 1 E⁺ act as hard and soft Lewis superacids, which readily interact with various hard and soft Lewis basic substrates. The rigid atrane framework stabilizes the localized positive charge on the elemental center and assists the formation of the well-defined highly coordinated states of 1 E⁺. The cations were applied to the hydrodefluorination, Friedel-Crafts reaction, alkyne cyclization, and carbonyl reduction as Lewis acid catalysts. Most notably, [ 1 Si][ClO₄] exhibits unique chemoselectivity that depends on a solvent in the competitive reaction of silyl enol ether with a mixture of benzaldehyde dimethyl acetal and benzaldehyde. Our findings indicate the potential of hard and soft Lewis superacids in organic synthesis.     

Oxygen Sorption and Desorption Properties of Selected Lanthanum Manganites and Lanthanum Ferrite Manganites

Temperature‐programmed desorption (TPD) with a carrier gas was used to study the oxygen sorption and desorption properties of oxidation catalysts and solid‐oxide fuel cell (SOFC) cathode materials (La_0.85Sr_0.15)_0.95MnO_3+δ (LSM) and La_0.60Sr_0.40Fe_0.80Mn_0.20O_3‐δ (LSFM). The powders were characterized by X‐ray diffractometry, atomic force microscopy (AFM), and BET surface adsorption. Sorbed oxygen could be distinguished from oxygen originating from stoichiometry changes. The results indicated that there is one main site for oxygen sorption/desorption. The amount of sorbed oxygen was monitored over time at different temperatures. Furthermore, through data analysis it was shown that the desorption peak associated with oxygen sorption is described well by second‐order desorption kinetics. This indicates that oxygen molecules dissociate upon adsorption and that the rate‐determining step for the desorption reaction is a recombination of monatomic oxygen. Typical problems with re‐adsorption in this kind of TPD setup were revealed to be insignificant by using simulations. Finally, different key parameters of sorption and desorption were determined, such as desorption activation energies, density of sorption sites, and adsorption and desorption reaction order.     

Rate constants and isotope effects for the reaction of H-atom abstraction from RH substrates by PINO radicals

The kinetics of the reactions of hydrogen atom abstraction from the C–H bonds of substrates of different structures by phthalimide-N-oxyl radicals is studied. The rate constants of this reaction are measured and the kinetic isotope effects are determined. It is shown that in addition to the thermodynamic factor, Coulomb forces and donor–acceptor interactions affect the reaction between phthalimide-N-oxyl radicals and substrate molecules, altering the shape of the transition state. This favors the tunneling of hydrogen atoms and leads to a substantial reduction in the activation energy of the process.     

Tris(pentafluorophenyl)borane [B(C6F5)3]-catalyzed Friedel-Crafts reactions of activated arenes and heteroarenes with α-amidosulfones: the synthesis of unsymmetrical triarylmethanes

Tris(pentafluorophenyl)borane [B(C₆F₅)₃] has found to be an efficient catalyst for Friedel-Crafts reactions between activated arenes or heteroarenes and α-amidosulfones. The products undergo further Friedel-Crafts reactions with activated heteroarenes leading to the synthesis of unsymmetrical triarylmethanes. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, highly regioselective, high yield, and broad applicability to various substrates.     

Synthesis and characterization of syndiotactic polystyrene-graft-poly(glycidyl methacrylate) copolymer by atom transfer radical polymerization

Syndiotactic polystyrene-graft-poly(glycidyl methacrylate) (sPS-graft-PGMA) copolymer was synthesized by a heterogenous atom transfer radical polymerization (ATRP) using 2-bromo-2-methylpropanoyl bromide modified syndiotactic polystyrene (BMPsPS) as macroinitiator and copper bromide combined with 2,2′-bipyridine as catalyst in anisole at room temperature. The macroinitiator with 7.0 mol% bromine content was prepared from Friedel-Crafts acylation reaction of sPS with 2-bromo-2-methylpropanoyl bromide in a heterogeneous process. It was found that BMsPS macroinitiator was well swelled in the mixture of anisole and GMA, the equilibrium swelling degree could reach 370%. The resultant polymer was characterized by FTIR and NMR spectroscopies. In addition, the thermal properties of the graft copolymers were also investigated with differential scanning calorimetry (DSC).