Aza-Diels-Alder reaction in fluorinated alcohols. A one-pot synthesis of tetrahydroquinolines

Hexafluoroisopropanol and trifluoroethanol are found to promote imino-Diels-Alder reactions of the N-aryl aldimine 1 with alkyl vinyl ethers to afford the corresponding tetrahydroquinolines in good yields without Lewis acid under mild and neutral conditions. The reaction is also efficient in a three component process from aldehyde, amine and vinyl ethers.     

Chloration d'un polyethylene ramifie influence de la temperature et du solvant

The chlorination of branched high-pressure polyethylenes, promoted by u.v. at various temperatures in carbon tetrachloride and 1,1–2,2 tetrachloroethane, has been studied. It has been possible to elucidate the influence of the temperature and the nature of the solvent on the characteristics of the chlorinated polymers.The chlorination is more efficient in carbon tetrachloride, where the efficiency of the u.v. is not affected by the medium.At the same degree of chlorination, the chain-breaking mechanisms are more important in carbon tetrachloride than in tetrachloroethane; they increase when the temperature of the medium increases. The chlorine-saturated polyethylene obtained in carbon tetrachloride is richer in 1,2 dichloroethylene sequences.Below 60°, the yield of chlorinated polymer is the same in the two solvents. Chlorination at higher temperature in tetrachloroethane does not improve the structural regularity or the yield of the chlorine-saturated polyethylenes.     

Improved method for the determination of sulfur components in natural gas

Determination of trace concentrations of sulfur components in natural gas is a true analytical challenge. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. In the present contribution the sample pretreatment and chromatographic separation steps have been evaluated and optimized based on the use of a flamebased sulfur chemiluminescence detector (SCD) for target compound detection. The proposed instrument consists of a programmed temperature vaporizing (PTV) injector employing a liner packed with Chromosorb 104, a 4 μm thick film apolar column and a flame-based SCD. Using a 13 mL sample loop the detection limit achievable with the new method is 3 μg S/m³. The precision of replicate measure. ments is generally in the range of 5–15% relative standard deviation. Lower detection limits can be achieved by preconcentrating larger sample volumes, e.g. 100 mL.     

Oxidation of isobutane catalyzed by vanadyl, copper and cesium substituted H3PMo12O40

Effects of Cs⁺, H⁺ and Cu²⁺ counterions in the vanadium containing heteropoly compounds Cs_xH_1-xVO[PMo₁₂O₄₀] and Cs_yH_0.5-yCu_0.25VO[PMo₁₂O₄₀] on the catalytic oxidation of isobutane and characterization by TGA, IR and ESR spectroscopies are reported. A high selectivity of 76% for methacrylic acid and methacrolein together has been obtained with Cs_0.75H_0.25VO[PMo₁₂O₄₀] catalysts at a reactivity of 5.3x10^-1 mmol/h cm³.     

Synthesis, structural, spectroscopic, and electrochemical characterization of high oxidation state diruthenium complexes containing four identical unsymmetrical bridging ligands

Six Ru2(6+) derivatives of the form Ru2(L)4(C[triple bond]CC6H5)(2), where L = 2-Fap, 2,3-F(2)ap, 2,4-F(2)ap, 2,5-F(2)ap, 3,4-F(2)ap, or 2,4,6-F(3)ap, are synthesized and characterized as to their electrochemical, spectroscopic, and/or structural properties. These compounds are synthesized from a reaction between LiC[triple bond]CC6H5 and Ru2(L)4Cl. Two of the investigated complexes exist in a (4,0) isomeric form while four adopt a (3,1) geometric conformation. These two series of geometric isomers are compared with previously characterized (4,0) Ru2(ap)4(C[triple bond]CC6H5)(2), (4,0) Ru2(F5ap)4(C[triple bond]CC6H5)(2), and (3,1) Ru2(F5ap)4(C[triple bond]CC6H5)(2). The overall data on the nine compounds thus provide an opportunity to systematically examine how the electrochemical and structural properties of these Ru2(6+) complexes vary with respect to isomer type and electronic properties of the bridging ligands.     

Etude des copolymeres (ethylene-hexene-1) par resonance magnetique nucleaire du proton et du carbone 13

Ethylene 1-hexene copolymers obtained by catalytic polymerization have been examined by ¹H and ¹³C NMR. Copolymer compositions have been determined by ¹H NMR and i.r. and the sequence distributions for 1-hexene by ¹³C NMR. Variations of the copolymer microstructure have been related to the experimental conditions for copolymerization.     

Synthesis and spectral characterization of some complexes of platinum(II) containing η-methyleugenol

Several complexes of the formula trans-[Pt(Meug)(Am)Cl₂], Meug: methyleugenol (4-allyl-1,2-dimethoxybenzene), a η²-coordinated olefin, and Am: ammine, methylamine, diethylamine, o-toluidine, m-toluidine, p-toluidine, o-anisidine, m-anisidine and p-anisidine have been prepared. UV, IR, Raman, ¹H NMR, ¹³C NMR and 2D NMR spectra of the complexes were recorded and analyzed.     

μ‐{N,N′‐Bis[2‐(dimethyl­amino)ethyl]oxamidato(2–)}‐1κ2O,O′:2κ4N,N′,N′′,N′′′‐bis­(4,4′‐dimethyl‐2,2′‐bipyridine‐1κ2N,N′)dinickel(II) bis­(perchlorate)

In the crystal structure of the title complex, [Ni₂(C₁₀H₂₀N₄O₂)(C₁₂H₁₂N₂)₂](ClO₄)₂ or [Ni(dmaeoxd)Ni(dmbp)₂](ClO₄)₂ {H₂dmaeoxd is N,N′‐bis­[2‐(dimethyl­amino)ethyl]oxamide and dmbp is 4,4′‐dimethyl‐2,2′‐bipyridine}, the deprotonated dmaeoxd²⁻ ligand is in a cis conformation and bridges two Ni^II atoms, one of which is located in a slightly distorted square‐planar environment, while the other is in an irregular octa­hedral environment. The cation is located on a twofold symmetry axis running through both Ni atoms. The dmaeoxd²⁻ ligands inter­act with each other via C—H⋯O hydrogen bonds and π–π inter­actions, which results in an extended chain along the c axis.     

Electrochemical and spectroelectrochemical characterization of Ru(2)(4+) and Ru(2)(3+) complexes under a CO atmosphere

Eleven different Ru(2)(4+) and Ru(2)(3+) derivatives are characterized by thin-layer FTIR and UV-visible spectroelectrochemistry under a CO atmosphere. These compounds, which were in-situ electrogenerated from substituted anilinopyridine complexes with a Ru(2)(5+) core, are represented as Ru(2)(L)(4)Cl where L = 2-CH(3)ap, ap, 2-Fap, 2,3-F(2)ap, 2,4-F(2)ap, 2,5-F(2)ap, 3,4-F(2)ap, 3,5-F(2)ap, 2,4,6-F(3)ap, or F(5)ap. The Ru(2)(5+) complexes do not axially bind CO while mono- and bis-CO axial adducts are formed for the Ru(2)(4+) and Ru(2)(3+) derivatives, respectively. Six of the eleven investigated compounds exist in a (4,0) isomeric form while five adopt a (3,1) geometric conformation. These two series of compounds thus provide a large enough number of derivatives to examine trends and differences in the spectroscopic data of the two types of isomers in their lower Ru(2)(4+) and Ru(2)(3+) oxidation states. UV-visible spectra of the Ru(2)(4+) derivatives and IR spectra of the Ru(2)(3+) complexes under CO are both isomer dependent, thus suggesting that these data can be used to reliably predict the isomeric form, i.e., (3,1) or (4,0), of diruthenium complexes containing four unsymmetrical substituted anilinopyridinate bridging ligands; this was confirmed by X-ray crystallographic data for seven compounds whose structures were available.     

Synthesis and Conformational Analysis of the Multidrug Resistance-Reversing Agent Hapalosin and Its Non-N-methyl Analog

Hapalosin was initially synthesized by macrolactonization, and a second synthesis was achieved by cycloamidation. In both syntheses, three of the five stereocenters in hapalosin were established by two Brown allylboration reactions. The synthesis of the non-N-Me analog of hapalosin involved chelation-controlled reduction of a gamma-amino-beta-keto ester and cycloamidation. In CDCl(3) at 25 degrees C, synthetic hapalosin exists as a 2.3:1 mixture of conformers, while its non-N-Me analog exists only as a single conformer. (1)H,(1)H-NOESY and computation reveal that the configuration of the amide bond is responsible for the conformations of the two compounds. The major conformer of hapalosin is found to be an s-cis amide, the minor conformer an s-trans amide, and the non-N-Me analog an s-trans amide. Applying distance constraints to protons that exhibit NOESY correlations, computation shows that the major conformer of hapalosin and the non-N-Me analog have very different conformations. By contrast, the minor conformer of hapalosin and the non-N-Me analog have very similar conformations.