Mathematical modeling of butadiene rubber synthesis process on neodymium-containing catalyst system

The synthesis of butadiene rubber mediated by a lanthanide catalyst system based on neodymium(III) chloride in a batch reactor was mathematically modeled. The mechanism of the process was identified and the rate constants of various reaction steps were determined. It was found that chain transfer reactions with different rate constants have an effect on the molecular-mass characteristics of butadiene rubber.     

Direct synthesis of nitrogen-containing filamentous carbon on a high-percentage Ni-Cu catalyst

Nitrogen-containing catalytic filamentous carbon (N-CFC) of chemical composition NC₁₈-NC₁₀₄ has been synthesized by the decomposition of pyridine (Py) from gaseous mixtures with argon or H₂ at 550–800°C on Ni/Al₂O₃ (Ni) and Ni-Cu/Al₂O₃ (Ni-Cu) high-percentage catalysts. The activity of the Ni-Cu catalyst in Py decomposition in mixtures with H₂ is about one order of magnitude higher than its activity in Py/Ar mixtures (more than 70 g N-CFC per metal gram in 4.5 h at 750°C), which is interpreted as arising from the nickel-catalyzed hydrogenation of Py. The formation and growth of carbon fibers occurs through the decomposition of Py (from Ar/Py mixtures) and/or Py hydrodenitrification products (from H₂/Py mixtures). The carbon material has been characterized by elemental analysis, low-temperature nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The effect of the noncatalytic reactions of Py and its transformation products on the composition and texture of N-CFC is discussed.     

Effect of polyvinylalcohols on the thermostability of lipase fromCandida rugosa

Lipase fromCandida rugosa was stabilized against thermal inactivation in the presence of polyvinylalcohols (PVA) of different molecular weights. The apparent rate constant of the lipase inactivation, k_d, at 49°C is 0.049/min and 0.022/min in the absence and in the presence of PVA (mol wt 22,000), respectively. The improvement of the lipase thermostability by adding PVA was confirmed by differential scanning calorimetry. The presence of PVA had also an effect on the hydrolytic activity of the enzyme. Furthermore, lipase was modified by covalent linkage to PVA by means of an original procedure. With respect to the native enzyme, the modified lipase has a slightly lower specific activity, but it is more stable against heat denaturation (k _d 0.032/min at 49°C).     

Deoxypegan-1-one derivatives. synthesis and borohydride reduction of 3-[(E)-arylmethylidene]-3,9-dihydropyrrolo[2,1-b]quinazolin-1(2H)-ones

3-[(E)-Arylmethylidene]-3,9-dihydropyrrolo[2,1-b]quinazolin-1(2H)-ones were prepared by reaction of quinazolyl-2-propionic acid hydrochloride with aromatic aldehydes in acetic anhydride in the presence of Et₃N. 3-[(E)-Arylmethylidene]-1,2,3,9-tetrahydropyrrolo[2,1-b]quinazolin-1-ols were formed by reduction of the 3-arylidene derivatives with sodium borohydride in methanol, readily lost water when heated with acids, and were converted into 3-[(E)-arylmethylidene]-3,9-dihydropyrrolo[2,1-b]quinazolines. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 463–467, September–October, 2006.     

Novel ruthenium(ii) and (iii) carborane complexes with diphosphine ligands and their application in radical polymerization

Ruthenium(ii) and (iii) carborane complexes containing XantPhos as a ligand were synthesized for the first time. It was shown that the reaction of the known complex exo-5,6,10-[Cl(Ph₃P)₂Ru]-5,6,10-(µ-H)₃-10-H-nido-7,8-C₂B₉H₈ with a 10% molar excess of XantPhos in benzene at 80 °C leads to a new closo-ruthenacarborane 3-Cl-3,3-[x²-XantPhos]-closo-3,1,2-RuC₂B9H₁₁, which can be easily converted to the corresponding acetonitrile complex 3-CH₃CN-3,3-[x²-XantPhos]-closo-3,1,2-RuC₂B₉H₁₁ by the reaction with isopropylamine in a dichloromethane—acetonitrile solvent mixture at 40 °C. These compounds, as well as previously synthesized ruthenium(ii) carborane complexes, were used as a basis for new catalyst systems allowing to conduct controlled radical polymerization at high rates even at low catalyst loading. The specific features of methyl methacrylate polymerization under the action of the indicated catalyst systems were considered and the mechanism of the process was investigated.

     

Synthesis of non-equilibrium PtxOs1−x Solid solutions. Crystal structure of [Pt(NH3)4][OsCl6]

Several non-equilibrium solid solutions belonging to the platinum-osmium systems Os_0.9Pt_0.1, Os_0.8Pt_0.2, Os_0.5Pt_0.5, Os_0.7Pt_0.3, Os_0.75Pt_0.25 are prepared and studied. The thermal decomposition of [Pt(NH₃)₄][OsCl₆] in the hydrogen and helium atmosphere is investigated. It is found that the Pt_0.5Os_0.5 solid solution develops through the formation of (NH₄)₂[OsCl₆] and a metallic phase based on Pt. The crystal structure of a double complex salt [Pt(NH₃)₄][OsCl₆] is studied (X8-APEX Bruker, 1508 independent reflections, R = 2.04%). Crystal data for PtOsN₄Cl₆H₁₂ are: a = 11.6216(5) Å, b = 11.0016(5) Å, c = 10.3819(5) Å, V = 1327.4(1) ų, space group Cmca, Z = 4, d _x = 3.333 g/cm₃. The coordination polyhedron around Os is octahedral: 〈Os-Cl〉 2.357 Å, ∠Cl-Os-Cl 89.5–90.5°, while around Pt it is square-planar: Pt-N 2.046 Å, ∠ N-Pt-N 89.59° and 90.41°.     

The viscosity and density of the methanol + n-nonane, ethanol + n-nonane, and ethanol + n-decane systems

This work presents the results obtained in measurements of the kinematic viscosity and density of the methanol-n-nonane, ethanol-n-nonane, and ethanol-n-decane systems at various temperatures and low n-alkane concentrations (within the concentration range of miscibility). The dynamic viscosities of these systems at 298.15 K were calculated according to free volume theory. The results substantiated the existence of an anomaly in the behavior of viscosity of the methanol-n-nonane system (positive Δlnη values) and its absence for the ethanol-n-alkane systems.     

Kinetics of the reaction of 4-nitrophenyl benzoates with 4-chlorophenol in the presence of potassium carbonate in dimethylformamide

The effect of the substituent in the benzoyl group on the relative rate and activation parameters of transesterification of substituted 4-nitrophenyl benzoates with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate was studied by the competing reaction technique. The whole series of benzoates showed the enthalpy-entropy compensation effect. 4-Nitrophenyl benzoates having electronacceptor substituents give rise to isokinetic relationship with an isokinetic temperature β of 382 K. The mechanism of the transesterification process is discussed.     

Preparation of ultramicro-, micro-, and supermicroporous carbon adsorbents by template procedure

The new template procedure for preparing ultramicro-, micro-, and supermicroporous carbon adsorbents is proposed on the basis of the use of two polymers with different thermal stabilities as a template matrix and a carbonizable carbon source. The polymeric template matrix is removed by thermal decomposition in the low-temperature pyrolysis of the polymer mixture, whereas the second polymer component of a mixture is transformed into a carbonizate. The resultant monolithic carbonizate is the polymeric matrix replica and represents a molecular-sieve ultramicroporous carbon adsorbent, which adsorbs water vapor at 293 K and does not adsorb nitrogen vapor at 77 K. The activation of this carbonizate with water vapor leads to a series of micro-and supermicroporous carbon adsorbents with a broad range of the parameters of a pore structure: BET specific surface area S _BET is 610–2130 m²/g, micropore volume W ₀ is 0.20–0.69 cm³/g, micropore half-width x ₀ (slit model) is 0.20–0.70 nm, mesopore specific area S _me is 20–1000 m²/g, and characteristic adsorption energy E ₀ is 15.6–27.4 kJ/mol. Original Russian Text ? O.K. Krasil’nikova, A.M. Voloshchuk, A.E. Evsyukhin, N.Y. Lomovsakaya, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 2, pp. 207–213.     

Structure and heat-induced transformations of phosphorus-doped polyantimonic acids

X-ray powder diffraction and thermogravimetry (TG) are used to study the solid compounds formed upon joint hydrolysis of antimony pentachloride and phosphoric acid in the molar ratio range of 1.35 < Sb/P < 12. The products retain the pyrochlore structure motif intrinsic to crystalline polyantimonic acid, the increasing phosphorus concentration deteriorates the degree of crystallinity of the products. Contributions of various factors into diffraction peak broadening are ascertained. The effect of phosphorus on the structure of the products is discussed on the basis of X-ray powder diffraction and TG data.