Hydrogenation of ethyl esters of 4-phenyl-and (2-furyl)-substituted 2,4-dioxobutyric acids at palladium black

The hydrogenation of ethyl 4-R-2,4-dioxobutyrates (R = phenyl, 2-furyl) at 5% Pt/Al₂O₃ catalyst, modified with cinchonidine, and at palladium black was investigated. The former had low activity under the conditions we tested. The main products during the hydrogenation of these compounds at palladium black are ethyl 4-R-2-hydroxy-4-oxobutyrates. The yield of the phenyl derivative amounts to 68.5%, while the yield of the corresponding 2-furyl derivative amounts to 97%. In the last case ethyl 2-hydroxy-4-oxo-4-(2-tetrahydrofuryl)butyrate was detected as impurity. The optimum conditions for the formation of ethyl 2-hydroxy-4-phenylbutyrate (yield 88.2%) were determined. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 655–659, May, 2006.     

Core/shell particles containing 3-(methacryloxypropyl)-trimethoxysilane in the shell: synthesis, characterization, and application

In comparison to the corresponding single-component counterparts, core/shell particles are widely used due to their better physical and chemical properties. The surface properties of core/shell particles evidently play an important role in the process of application. It is easy to deduce that surface properties mostly depend on the properties of the component in the shell. Therefore, desirable materials of shell are very significant for the study of composite materials, especially in core/shell field. It is well known that polysiloxane has excellent properties, such as the water repellency, high flexibility, low surface energy, and biocompatibility. Its application, however, is limited due to poor cohesiveness and poor film-forming properties. Recently, much endeavor has been made to overcome such flaws. It is found that polyacrylate is commonly considered for its good cohesiveness and excellent film-forming property. The combination of polysiloxane and polyacrylate has been shown to be important in the composite material field, especially as core/shell particles. Unfortunately, their hydrophobicity is considerably different and thus, the core/shell particles consisting of polyacrylate (PA)/polysiloxane (PSi) are hard to prepare by general seeded emulsion polymerization, and are also scarcely available in the literature. In this study, the new core/shell PA/PSi particles with poly(butyl methacrylate) (PA) as the core and poly(3-(methacryloxypropyl)-trimethoxysilane) (PSi) as the shell were prepared by dispersion polymerization under the kinetically controlled conditions. The characterization of the particles by TEM, DSC, particle size analyzer as well as static contact angle confirmed the formation of core/shell structure. The application of core/shell (PA/PSi) particles also has been considered and discussed here.TEM micrographs of core/shell (PA/PSi) particles.     

Trimethylsilylcyclopentadienylchromium(III) complexes with diphenyl-2-pyridylphosphine: synthesis, structural characterisation and catalytic behaviour of [(C6H5)2PC5H4NH][(η-Me3SiCp)CrCl3]

Reaction of CrCl₃ with LiCpSiMe₃ in THF leads to the formation of a solvated intermediate, [(η⁵-Me₃SiCp)CrCl₂(THF)], which in turn reacts with diphenyl-2-pyridylphosphine to yield the complex [(C₆H₅)₂PC₅H₄NH][(η⁵-Me₃SiCp)CrCl₃] (1) in 66% yield. As a secondary product was isolated the neutral complex [(η⁵-Me₃SiCp)CrCl₂{(C₆H₅)₂PC₅H₄N}] (2) in 5% yield. The structure of complex 1 has been determined by single crystal X-ray diffraction. In the anion the metal centre shows a pseudo-octahedral geometry with the centroid of the trimethylsilylcyclopentadienyl ligand occupying the centre of three octahedral sites, and three chloride atoms completing the co-ordination sphere. Complex 1 in the presence of MAO leads to the formation of an active catalyst for the polymerization of ethylene.     

Hydrogen elimination in cyclopentadienylnickel compounds as a route to organonickel and organic compounds

Reactions of -, β- and γ-hydrogen elimination in cyclopentadienylnickel compounds formed in the reactions of nickelocene with lithium or magnesium compounds are discussed. Elimination of -hydrogen from CpNiR where R is CH₃, CH₂C(CH₃)₃, CH₂Si(CH₃)₃, CH₂Ph or CH=C(CH₃)₂ leads to the formation of trinickel clusters (CpNi)₃CR′, bis(cyclopentadienyl)(μ-cyclopentadiene)dinickel and (η⁵-cyclopentadienyl)(η³-cyclopenteny)nickel. β-hydrogen and γ-hydrogen elimination in vinylnickel compounds not possesing -hydrogen have been studied. Elimination and transfer of hydrogen forms (η³-allyl)(η⁵-cyclopentadienyl)nickel compounds. The mechanisms of these reactions are discussed.     

Synthesis and kinetics of polymerization of unsaturated monomers with OH groups in their structure: I.3-hydroxyneopentyl acrylate

The synthesis of new unsaturated monomers containing functional groups has been theoretically analyzed by considering a simple kinetic scheme. In the reactions between acetyl and acryloyl chloride with neopentylglycol, it was shown that the comparison between theoretical and experimental results, does not allow us to conclude that the two rate constants controlling the reactions are equivalent. Kinetic experiments of the polymerization of 3-hydroxyneopentyl acrylate were carried out in benzene and 1,4-dioxane solution at different temperatures. Dilatometric techniques and nonlinear least-squares methods were used to obtain kinetic data and to determine the kinetic constants, respectively. The values of $k_p /k_t^{1/2}$ for this monomer were found higher in dioxane than in benzene due, probably, to the fact that in the last solvent the polymerization is heterogeneous. The activation energy, determined by using different values of $k_p /k_t^{1/2}$ was found 7.6 kcal/mol. The stereostructure of the polymers derived from 3-hydroxyneopentyl acrylate and 3-acetoxyneopentyl acrylate was determined by ¹³C-NMR spectroscopy from the analysis of the resonance signals belonging to the carbonyl groups, obtaining values for the fraction of isotactic dyads in the range 0.36 ± 0.03 for both polymers. Finally, the glass transition temperatures of both polymers, determined calorimetrically, were found 281 and 255 K, respectively. © 1994 John Wiley & Sons, Inc.     

Quantitative aspects of gradient HPLC of copolymers from styrene and ethyl methacrylate

Summary Prerequisite of quantitative evaluation in chromatography is equivalence of sample composition and detector signal. This includes complete retention and proper elution of all sample constituents. In polymer HPLC, complete retention requires a poor starting eluent, a sufficiently active column, and a low ratio of injection volume to column volume. On small pore columns, insufficient retention caused the polymer to elute either in the interstitial volume (sample exclusion), together with the sample solvent, or immediately after the solvent plug.Stat-copoly(styrene/ethyl methacrylate) samples are more difficultly retained thanstat-copoly(styrene/acrylonitrile) specimes. With the former copolymer it could be shown that incomplete retention did not cause sample demixing. In order to gain complete retention, non-exclusion HPLC of polymers should be performed with columns whose solvent volume is at least 50 times as large as the injection volume. This consequence is of practical importance in chromatographic cross-fractionation where rather large volumes of SEC eluate are injected into the apparatus for gradient HPLC.     

Immobilization of endo-1,4-β-xylanase on polysulfone acrylate membranes: Synthesis and characterization

We report on a new enzyme/support system to immobilize proteins such as enzymes through a covalent bond on polysulfone membranes. In the present case the enzyme endo-1,4-β-xylanase (E.C.3.2.1.8) is attached to polysulfone previously derivatized by introducing an acrylate group. Membranes are properly prepared from this polysulfone acrylate. Afterwards the enzyme is immobilized though the amino groups of side chains of the amino acids of the enzyme and the acrylate group of the derivatized polysulfone. Such immobilization of the enzyme is confirmed by microelemental analysis as well as by amino acid analysis by HPLC. Moreover, the enzymatic activity of the membranes was evaluated and compared with that corresponding to the free enzyme. Certain physical parameters (asymmetry, irregularity, pore size and surface roughness) of the corresponding enzymatic membranes were obtained from SEM and AFM image interpretation.     

Thermal degradation of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers

Vinylidene chloride polymers containing comonomer units capable of consuming evolved hydrogen chloride to expose good radical-scavenging sites might be expected to display greater thermal stability than similar polymers containing simple alkyl acrylates as comonomer. Incorporation of a comonomer containing the phenyl t-butyl carbonate moiety into a vinylidene chloride polymer has the potential to afford a polymer with pendant groups which might interact with hydrogen chloride to expose phenolic groups. Copolymers of vinylidene chloride with [4-(t-butoxycarbonyloxy)phenyl]methyl acrylate have been prepared, characterized, and subjected to thermal degradation. The degradation has been characterized by thermal and spectroscopic techniques. The degradation of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers is much more facile than the same process for similar copolymers containing either [4-(isobutoxycarbonyloxy)phenyl]methyl acrylate or methyl acrylate, a simple alkyl acrylate, as comonomer. During copolymer degradation, [4-(t-butoxycarbonyloxy) phenylmethyl acrylate units are apparently converted to acrylic acid units by extensive fragmentation of the sidechain. Thus, the phenyl t-butyl carbonate moiety does function as a labile acid-sensitive pendant group but its decomposition in this instance leads to the generation of a phenoxybenzyl carboxylate capable of further fragmentation.     

Fluorinated monomer–styrene copolymer latex particles: I. kinetic studies in a soap-free aqueous medium

Soap-free emulsion copolymerization of 2, 2, 2-trifluoroethyl acrylate (3FEA) with styrene was carried out by using potassium persulfate as an initiator, and the effects of the weight fraction of 3FEA in the monomer feed on the kinetics and the particle size were investigated. Monomer conversions were followed by a gravimetric method, revealing that the overall polymerization rate increased exponentially with an increase in the weight fraction of 3FEA. According to dynamic light scattering measurement, the final particle size was found to decrease with an increase in the weight fraction of 3FEA. The number of particles for 3FEA homopolymerization was roughly twice as large as that at the fraction of 0.9, although both fractions had the almost same polymerization rates. These results indicate that soap-free emulsion homopolymerization of 3FEA would proceed not only inside the polymer particles but also in the aqueous phase throughout the polymerization.     

Mixed-metal cluster chemistry. 26 . Proclivity for “all-terminal” or “plane-of-bridging-carbonyls” ligand disposition in tungsten-triiridium clusters

Reaction of WH(CO)₃(η-C₅Me₅) with IrCl(CO)₂(4-H₂NC₆H₄Me) affords WIr₃(μ-CO)₃(CO)₈(η-C₅Me₅) in low yield. A structural study reveals a WIr₂-centred plane of bridging carbonyls, in contrast to the crystal structure of WIr₃(CO)₁₁(η-C₅H₅) (all-terminal carbonyl distribution). DFT calculations reveal an increasing proclivity to adopt an all-terminal CO disposition for clusters MIr₃(CO)₁₁(η-C₅H₅) in the gas phase on proceeding from M=Cr to Mo and then W, consistent with structural studies in the solid state for which the tungsten-containing cluster is the only all-terminal example. Increasing electron donation from the ligands in the tungsten system (either from phosphine substitution or cyclopentadienyl permethylation) suffices to impose a plane of bridging carbonyls in the ground state structure. ¹³C NMR fluxionality studies reveal that CO exchange mechanism(s) for WIr₃(CO)₁₁(η-C₅H₅) and the related tetrahedral cluster W₂Ir₂(CO)₁₀(η-C₅H₅)₂ are very fast and involve all carbonyls on the clusters. DFT calculations on MIr₃(CO)₁₁(η-C₅H₅) (M=Cr, Mo) substantiate a ‘merry-go-round’ mechanism for carbonyl scrambling in these systems, a result which is consistent with the scrambling behaviour seen in the NMR fluxionality studies on the W-containing congener.