Solidification of metallic tin in dispersed phase

Differential scanning calorimetry (DSC) and particle size measurements were carried out on disproportionation products of pure SnO to investigate the fusion and solidification behaviour of Sn droplets and their catalytic nucleation on Sn oxides. If disproportionation reaction takes place at T ≥ 798 K, the products are metallic Sn and SnO₂; but for 523 < T < 798 K, SnO₂ is replaced by an intermediate oxide (IO) Sn_xO_(1+x). On melting, samples with IO show a drop of melting point of metallic tin due to Gibbs–Thomson effect; no lowering of melting point was observed in samples with SnO₂. On the other hand, if solidification occurs in the presence of IO, Tin droplets always displayed three distinct exothermic solidification peaks, but if it takes place in the presence of SnO₂, only one exothermic peak is observed. Undercooling values and contact angles were determined for each of the heterogeneous nucleation processes. The different behaviour of metallic Tin droplets was related to the different lattice symmetry of SnO₂ and IO, which act as nucleation catalysts.     

Ln2O3/Al2O3催化酯化合成邻苯二甲酸二辛酯

Ｌｎ_２Ｏ_３／Ａｌ_２Ｏ_３催化酯化合成邻苯二甲酸二辛酯陈其瑞，张凤美，罗明润，焦肇林（安徽师范大学化学系，芜湖２４１０００）关键词稀土氧化物，担载催化剂，催化酯化，邻苯二甲酸二辛酯邻苯二甲酸二（２－乙基己醇用酯（Ｄｉｏｃｔｙｌｐｈｔｈａｌａｔｅ）是一...     

Polymer-supported calix[4]arenes for sensing and conversion of NO2/N2O4

The use of simple calix[4]arenes 1a,b for NO₂/N₂O₄ sensing and conversion is demonstrated, both in solution and in the solid state. Upon reacting with these gases, compounds 1a,b encapsulate reactive NO⁺ cations within their cavities with the formation of deeply colored (λ_max∼570 nm) charge-transfer complexes 2a,b. Further functionalization of the calix[4]arene platform is reported for attachment to solid supports. Polymer-supported calixarene material 3 was prepared, which reversibly traps NO₂/N₂O₄ with the formation of nitrosonium storing polymer 4. Material 4 was effectively used for nitrosation of amides.     

Some neutral three-coordinate complexes of mercury(II) halides and pseudohalides with N-methylnicotinamide

Coordination compounds of mercury(II) chloride, bromide, cyanide and thiocyanate with N-methylnicotinamide, a potentially bidentate ligand, have been prepared. The complexesisolated have 1∶1 (metal:ligand)stoichiometry. Molecular weight measurements in molten camphor indicate that the mercury (II) chloride and bromide complexes are monomeric. Based on conductance values, molecular weight determinations and infrared spectral data, it is inferred that in the solid state in all these complexes the metal ion has a coordination number three and is bonded to the N-methylnicotinamide via its pyridine ring nitrogen, and is terminally bonded to the halogen/pseudohalogens.     

Palladium-benzimidazolium salt catalyst systems for Suzuki coupling: development of a practical and highly active palladium catalyst system for coupling of aromatic halides with arylboronic acids

Palladium-benzimidazolium salt catalyst systems have been studied for the Suzuki coupling. A different substitutent effect has been uncovered with respect to nitrogen substituents in the benzimidazolium salts from the palladium-imidazolium salt analogs. A practical and highly active palladium catalyst system, PdCl₂/N,N′-dibenzylbenzimidazolium chloride 2, has been identified for the Suzuki coupling of aromatic halides with arylboronic acids. The coupling of a wide array of aromatic halides with arylboronic acids with the PdCl₂-2 catalyst system gave good to excellent yields. The effective palladium loading could be as low as 0.0001 mol% and 0.01-0.1 mol% for iodide and bromide substrates, respectively. The coupling of unactivated aromatic chlorides with arylboronic acids also gave good results using Cs₂CO₃ as base with a 2 mol% palladium loading. The electronic factors from aromatic halides exert a significant influence on the Suzuki coupling catalyzed by the PdCl₂-2 system while the electronic effect from the arylboronic counterparts is negligible. The aromatic halides with modest steric hindrance could also couple smoothly with phenylboronic acids using the PdCl₂-2 catalyst system.     

Nanorods of Various Oxides and Hierarchically Structured Mesoporous Silica by Sol-Gel Electrophoresis

In this paper, we report the template-based growth of nanorods of oxides and hierarchically structured mesoporous silica, formed by means of a combination of sol-gel processing and electrophoretic deposition. Both single metal oxides (TiO₂) and complex oxides (Pb(Zr_0.52Ti_0.48)O₃) have been grown by this method. This method has also been applied to the growth of nanorods of mesoporous silica having an ordered pore structure, where the pores are aligned parallel to the long axis of the nanorod. Uniformly sized nanorods of about 125–200 nm in diameter and 10 m in length were grown over large areas with near unidirectional alignment. Appropriate sol preparation yielded the desired stoichiometric chemical composition and crystal structure of the oxide nanorods, with a heat treatment (500–700°C for 15–30 min) for crystallization, densification and any necessary pyrolysis.     

The first palladium-catalyzed Sonogashira coupling of unactivated secondary alkyl bromides

A palladium-carbene catalyzed Sonogashira coupling of unactivated alkyl bromides with alkyl substituted alkynes is reported. For the first time, unactivated secondary alkyl halides were successfully employed in Sonogashira reactions.     

New hybrid chelating sorbents with grafted 3-aminopropionate groups based on mixed silicon,aluminum, titanium,or zirconium oxides

A series of new hybrid organo-inorganic sorbents with the 3-aminopropionate chelating group was synthesized. The synthesis includes the copolycondensation (sol—gel method) of tetraethoxysilane, 3-aminopropyltriethoxysilane, and several modifiers (MeSi(OEt)₃, EtSi(OEt)₃, Ti(OEt)₄, AlONO₃, ZrOCl₂) followed by carboxyethylation with acrylic acid. The obtained chelating sorbents were characterized by elemental analysis, FT-IR and ¹H NMR spectroscopy, and thermogravimetry. The N-carboxylated sorbents have a higher sorption capacity with respect to metal ions (0.5–0.9 mmol g⁻¹, pH 6.3, NH₄OAc, 20 °C) than the starting sorbents with the primary amino group (0.05–0.2 mmol g⁻¹) and manifest high selectivity for copper(II) ion extraction. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1783–1788, August, 2005.     

Oxidation of mandelic acid derivatives catalysed by Bi(0)/O2 systems: mechanistic considerations

Mandelic acid and some aryl substituted derivatives were oxidised under molecular oxygen and a catalytic amount of Bi(0). The corresponding aldehydes and/or the carboxylic acids were obtained selectively depending on the nature of the substituent. Aldehydes and α-keto acids were oxidised under the same Bi(0)/O₂ system and α-keto acids were proposed as intermediates in the formation of benzoic acid derivatives.