Universal Brønsted-Evans-Polanyi Relations for C–C,C–O,C–N,N–O,N–N,and O–O Dissociation Reactions

Abstract  

It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.     

Hydrothermal Synthesis of a Nano-sized Mercury(II) N–N–O Donor Coordination Compound

A novel nano-structures mercury(II) coordination compound, [Hg (HPCIH) I₂] (1), (“HPCIH” is the abbreviation of 2-pyridinecarbaldehyde isonicotinoyl hydrazone) has been synthesized by a hydrothermal method that produces the coordination compound at nano size. The new nanostructure was characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction elemental analysis and IR spectroscopy. Compound 1 was structurally characterized by single crystal X-ray diffraction and the single-crystal structure of this complex shows that each mercury(II) center is five coordinated with two N-donor and one O-donor atoms from “HPCIH” ligand and two iodo anions. Self-assembly of this complexes is realized by CH····I, I····I and π–π stacking interactions. The supramolecular features in these complexes are controlled by weak directional intermolecular interactions.     

Rh–Sr/Al2O3 Catalyst for N2O Decomposition in the Presence of O2

The improving effect of Sr in the catalytic activity of Rh for N₂O decomposition has been studied under 1,000 ppm N₂O/He and 1,000 ppm N₂O/5% O₂/He (GHSV = 10,000 h^?1). Different techniques have been used for catalysts characterization: TEM, SEM-EDX, XRD, N₂ adsorption at ?196 °C and in situ XPS. Sr favours the Rh dispersion and reduction under reaction conditions, and allows the low temperature removal of N₂O in the presence of O₂ (100% decomposition at 350 °C).     

Atomistic analyses of the effect of temperature and morphology on mechanical strength of Si–C–N and Si–C–O nanocomposites

3-D molecular dynamics (MD) analyses of SiC–Si₃N₄ nanocomposite deformation and SiCO nanocomposite deformation are performed at 300 K, 900 K, and 1500 K. In SiC–Si₃N₄ nanocomposites, distribution of second phase SiC particles, volume fraction of atoms in GBs, and GB thickness play an important role in temperature dependent mechanical behavior. The deformation mechanism is a trade-off between the stress concentration caused by SiC particles and Si₃N₄–Si₃N₄ GB sliding. The temperature increase tends to work in favor of GB sliding leading to softening of structures. However, microstructural strength increases with increase in temperature when GBs are absent. In the case of SiCO nanocomposites, findings indicate that temperature change dependent amorphization of nanodomains, the nanodomain wall placement, the nanodomain wall thickness, and nanodomain size are important factors that directly affect the extent of crystallinity and the strength against mechanical deformation.     

Transition-metal-catalyzed C–N cross-coupling reactions of N-unsubstituted sulfoximines: a review

ABSTRACT

In recent years, N-functionalized sulfoximines have attracted the significant attention of medicinal chemists due to their wide spectrum of biological activities. This class of organosulfur compounds has also found a number of applications in agricultural chemistry. In addition to these benefits, sulfoximines are one of the most important and versatile chiral auxiliaries and ligands in asymmetric syntheses. As a result of these, numerous efforts have been devoted to the development of effective strategies towards the synthesis of N-functionalized sulfoximines. An efficient, practical, and versatile strategy for the synthesis of titled compounds involves the transition-metal-catalyzed cross-coupling reactions of easily accessible NH-sulfoximines with various electrophilic partners. In this review, we highlight a number of recent discoveries and advances in this interesting and important research arena. The N-alkylation reactions are discussed first. This is followed by metal-catalyzed N-alkenylation and N-alkynylation reactions. Finally, N-arylation reactions will be covered at the end of the review.     

Catalytic Performance of Aged Rh/CeO2–ZrO2 for NO–C3H6–O2 Reaction Under a Stoichiometric Condition

The activity of Rh/CeO₂ for NO reduction by C₃H₆ was gradually deceased by mixing with ZrO₂ until 68 mol%. Rh supported on CeO₂–ZrO₂ with higher OSC was found to show lower catalytic activity. High OSC of CeO₂–ZrO₂ would probably stabilize the surface of Rh in oxidized state, resulting in low activity and low efficiency of C₃H₆ utilization for NO reduction. In situ FT-IR spectroscopy suggested that mononitrosyl species such as Rh(NO)^δ? and Rh(NO)^δ+ are reaction intermediates in the NO–C₃H₆–O₂ reaction over Rh/CeO₂–ZrO₂ catalysts.     

Oxidation behaviour of ceramic fibres from the Si–C–N–O system and related sub-systems

The oxidation of Si–C–N–O fibres has been investigated. The oxidation rates and the activation energies for the Si–C–O system are similar to those for crystalline SiC. The oxygen and the free carbon concentrations in the ceramics have a limited influence on the oxidation behaviour. As long as the formed silica scale is protective, oxidation kinetics are essentially controlled by the diffusion of oxygen through SiO₂. The parabolic rates in the Si–C–N–O and Si–N–O systems are lower and their activation energies higher than those for SiC. Their values strongly depend on the ratios of C and N bonds to Si and continuously vary from those for SiC (E_a=110−140kJ mol⁻¹) to Si₃N₄ (E_a=330–490 kJ mol⁻¹). The oxidation mechanism might be related to a complex diffusion/reaction regime via the formation of an intermediate silicon-oxynitride (like for Si₃N₄) or silicon-oxycarbonitride layer. The oxidation behaviour of such complex systems is not significantly influenced by the oxygen nor the free carbon contents. It might be governed by the C/Si and N/Si ratios, limiting the nitrogen concentration gradient of the silicon-oxy(carbo)nitride sub-layer and therefore affecting the diffusion/reaction rates.     

Viscosity of high-nitrogen content Ca–Si–O–N glasses

The viscosity of three high-nitrogen content Ca–Si–O–N glasses, with 30–58 e/o N and 36–39 e/o Ca, was determined by micro-indentation. The measurements were made using an automated set-up, designed and built in-house, capable of measurements up to 1200 °C with applied loads of 0.01–15 N. The viscosity increases significantly with the nitrogen content and reaches viscosity values close to reported values for rare-earth silica oxynitride glasses. The glass transition temperatures range between 878 and 995 °C and are in very good agreement with values measured by differential thermal analysis. The apparent viscosity activation energies are very high, ranging from 855 to 2170 kJ/mol. The glasses can accordingly be classified as being both very refractory and very fragile. Implications of the viscosity values and mechanical properties of the glasses for their structures are discussed.     

First example of a CLICK reaction of a coordinated 4′-azido-2,2′:6′,2″-terpyridine ligand

The first example of a copper-catalysed [2 + 3] cycloaddition reaction of a coordinated 4′-azido-2,2′:6′,2″-terpyridine ligand is reported and the solid state structures of the precursor and product are described.     

Facile C–N cleavage reactions of secondary and tertiary alkyl amines by P,O chelating rhodium and iridium complexes

The reactions of Cp*MCl(MDMPP-P,O) (1: M=Rh; 3: M=Ir; MDMPP-P,O=PPh₂(C₆H₃-2-O-6-MeO)) with secondary or tertiary alkyl amine (R₂NH or R₃N) in the presence of KPF₆ underwent a C–N cleavage of amine to afford primary amine complex [Cp*M(MDMPP-P,O) (RNH₂)](PF₆) (2: M=Rh; 4: M=Ir).     

Cold sintering of the Mg–C–O–H system

The cold sintering process reproduces the formation of sedimentary rocks in the Earth's crust by molding raw powder and a small amount of solvent at temperatures of about 300 °C or less under uniaxial pressure of several hundred megapascals. Generally, carbonates and hydroxides cannot be hardened by conventional sintering process due to thermal decomposition. In contrast, when this cold sintering process is selected, since the densification of the starting powder can be achieved by a dissolution-precipitation reaction with water as a solvent, carbonates and hydroxides can be hardened at temperatures below their decomposition temperatures. In the Mg–C–O–H system, magnesium hydroxide and a basic magnesium carbonate were selected as starting compounds, and the mechanism of their densification by a cold sintering process was investigated. The average compressive strength of the obtained magnesium hydroxide solidified products after cold sintering at 250 °C and 270 MPa for 60 min, and basic magnesium carbonate solidified products after cold sintering at 150 °C and 270 MPa for 60 min, were 121 MPa (84% relative density) and 275 MPa (88% relative density), respectively. The added water was found to play an important role in promoting a solution-precipitation process inside the magnesium hydroxide or basic magnesium carbonate powder compact, resulting in low-temperature sintering to form hardened bodies in the Mg–C–O–H system.     

DRIFT Studies of Adsorbed CO Over Sulfided K–Rh–Mo/Al2O3 Catalysts: Detection of Rh–Mo–S Phase

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to study the nature of active species in K–Rh–Co–MoS₂/Al₂O₃ catalyst by means of probing with CO molecule. The effects of K addition to Rh and interaction between Mo and Rh were studied with varying K and Mo loadings over 1 wt% Rh/Al₂O₃ catalyst. In sulfided Rh–Mo/Al₂O₃, the formation of Rh–Mo–S phase was evidenced first time by a band at 2,095 cm^?1. The introduction of Co to K–Rh–MoS₂/Al₂O₃ catalyst showed the existence of both Rh and Co promoted MoS₂ sites, but the CO absorption frequencies in DRIFT spectra are significantly at lower side compared to Co free Rh–Mo catalyst. The stabilities of CO band from Rh and Co promoted and unpromoted MoS₂ sites are studied at different temperatures. When activated carbon used as support, bands for both promoted and unpromoted MoS₂ sites were appeared, but the intensity of these bands were decreased largely compared to alumina based catalyst, resulted from the coverage of added K not only on the support surface but also on the active metal components due to the neutral nature of activated carbon.     

Chemical Stability of ZnO–Na2O–SO3–P2O5 Glasses

We report on chemical stability and corrosion behavior of highly depolymerized sulfophosphate glasses from the system ZnO–Na₂O–SO₃–P₂O₅ in aqueous solution, providing data on weight loss, ion release rates, and modifications of surface topology as a function of time, temperature and pH value. Observations seem consistent with the previously developed structural model of chemical heterogeneity, where cations Na⁺ and Zn²⁺ cluster selectively in the vicinity of sulfate and phosphate anions, respectively.     

Quantitative EFTEM study of precursor-derived Si–B–C–N ceramics

Ceramic materials derived from a boron modified polysilazane were investigated by means of energy-filtering transmission electron microscopy (EFTEM). After cross-linking of the polymer and subsequent thermolysis, a coarse powder with average composition Si_24.0B_8.0C_44.0N_24.0 is obtained. For further investigation, monolithic particles with sizes of several millimeters were heat treated in crucibles under a flowing nitrogen atmosphere at 1800 °C for 10 h. During thermolysis, the particles developed internal cracks on the macroscopic scale. At the crack surfaces, a layer of pure carbon was found. In the crack-free region, the material is composed of Si₃N₄ and SiC nano crystallites which are embedded in a turbostratic BNC-matrix. Quantitative electron spectroscopic imaging (ESI) shows an atomic ratio of the elements B:C:N of 1.0:4.0:1.1 in this matrix. In the vicinity of the cracks, silicon nitride locally decomposes with formation of silicon carbide because of its reaction with excess carbon. A detailed EFTEM study of the phase distribution near the crack surfaces showed that the first Si₃N₄ crystallites occur at a distance of approx. 5 μm from the carbon covered crack surface. In additional experiments the composition of the BNC-layers as a function of the distance from the crack surface was investigated.     

Formation of diamond from CaCO3 in a reduced C–O–H fluid at HP–HT

The formation of diamond from CaCO₃ was studied in a reduced C–O–H fluid mainly composed of CH₄ and H₂O under diamond-stable HP–HT conditions at 7.7 GPa and 1500 °C in order to examine the genesis of natural diamonds experimentally and to present a new synthesis process of diamond. As a result, CaCO₃ was reacted with reduced C–O–H fluid very rapidly, and most of the starting CaCO₃ was converted to Ca(OH)₂ and C within 1 h. The elemental carbon thus formed was graphite although the experiments were carried out deep in the diamond-stable HP–HT region, but it was transformed to diamond after 12 h. Graphite and diamond had the morphology characteristics of solution growth: the former was flaky and a few μm in size, and the latter was octahedral with sharp edges and flat surfaces and a few tens of μm in size.     

含Si–O–C界面层的C/Si–C–N复合材料的抗氧化性能(英文)

为了研究利用Si–O–C界面层来提高碳纤维增强陶瓷基复合材料的抗氧化性能,利用化学气相浸渗和聚合物浸渗裂解工艺制备了以Si–O–C为界面的碳纤维增强Si–C–N陶瓷基复合材料（C/Si–O–C/Si–C–N）和无界面层的碳纤维增强Si–C–N陶瓷基复合材料（C/Si–C–N）。研究了C/Si–O–C/Si–C–N和C/Si–C–N在600、900℃和1 200℃空气环境中的氧化行为。结果表明：采用Si–O–C界面层后可提高复合材料的抗氧化性能;Si–O–C界面层较高的氧化抗力是碳纤维增强Si–C–N复合材料抗氧化性能提高的主要原因。     

The dielectric,thermal properties and crystallization mechanism of Li–Al – B–Si – O glass – Ceramic systems as a new ULTCC material

Li–Al–B–Si–O (LABS) glass-ceramics with a sintering temperature of 600 °C were studied for ultra-low temperature co-fired ceramics (ULTCC) applications. The crystal phase of LABS glass-ceramics is dendritic β-spodumene. The permittivity and dielectric loss of LABS glass-ceramics are ε_r = 5.8 and tgδ = 1.3 × 10⁻³ at 10 MHz, respectively. The coefficient of thermal expansion (CTE) of LABS glass-ceramics is 3.23 ppm/°C, which is close to that of silicon. The dielectric and thermal properties of LABS glass-ceramics are closely correlated to the degree of its crystallization. The permittivity decreases continually while the dielectric loss decreases first and slightly increases with the increasing of crystallization of β-spodumene. The CTE of LABS glass-ceramics decreases as β-spodumene crystallized from LABS glass. The crystallization kinetic and mechanism of LABS glass-ceramics indicate that the β-spodumene crystallizes in a two-dimensional interfacial growth mechanism due to the migration of Li-ions. The diffusion coefficients derived from energy-dispersive X-ray spectroscopy (EDS) results indicated that both Al and Ag electrodes have good compatibilities with ULTCC tapes, which could reduce the cost of multilayer electro-ceramic devices dramatically by using the ULTCC and base metallization.     

Microstructure and mechanical properties of Al2O3–Ti(C,N)–cBN composites prepared by a novel hot-forging process

Al₂O₃–cBN has received considerable attention in the field of ceramic cutting tools due to its high hardness, high wear resistance, and low cost, but poor interfacial bonding affects the performance of the composite. In this study, a novel hot-forging process was used to prepare high-performance Al₂O₃–cBN composites using Ti(C,N) as a binder. The evolution of the morphology, phase, and microstructure of the hot-forged Al₂O₃–Ti(C,N)–cBN composites was determined, and the mechanical properties were measured. The relative density of the composites increases significantly after hot forging, and the deformation of the composites increases with the hot-forging temperature. The highest performing Al₂O₃–Ti(C,N)–cBN composite was prepared by hot forging at 1600°C and has a hardness of 20 GPa, a bending strength of 647 MPa and a fracture toughness of 5.37 MPa m^1/2, which are superior to those of a directly hot-pressed sintered composite. However, at hot-forging temperatures higher than 1700°C, Al₅O₆N and TiB₂ are formed in the composite. In the composite hot forged at 1800°C, serrated grain boundaries promote the strength and toughness of the composite to 877 MPa and 6.76 MPa m^1/2, respectively. Therefore, the novel hot-forging process is expected to enhance material properties.     

Preparation and Performance of a P–N Containing Intumescent Flame Retardant Based on Hydrolyzed Starch

Halogen-free flame retardant is receiving an increased attention recently due to its hypotoxicity and high efficiency. Intumescent flame retardant is a hot spot in research of the halogen-free flame retardant. In this work, a P–N containing intumescent flame retardant named hydrolyzed starch phosphamide from melamine was synthesized via hydrolysis of starch, phosphorylation of the starch with phosphorus oxychloride, and the reaction between the phosphorylated starch and melamine. PU/hydrolyzed starch phosphamide from melamine composites was prepared using different additive amounts of hydrolyzed starch phosphamide from melamine. Fourier transform infrared, scanning electron microscopy, and thermogravimetric analysis were used to characterize the structures and thermal stabilities of related compounds. Flame retardation performance of hydrolyzed starch phosphamide from melamine was investigated by UL94, limit oxygen index test, and cone calorimetry. Result shows that the PU/hydrolyzed starch phosphamide from melamine composites with 30.0 php of hydrolyzed starch phosphamide from melamine got a limit oxygen index of 29.0 and UL94-V0 ranking. Heat release rate, rate of smoke release, and total smoke release were decreased distinctly.