bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of ΔpKa and of the molar volume of the base on the viscosity and on the concentration of conducting ions in binary mixtures of phenols and aliphatic amines
Authors: Huyskens P. L. , Neven L. 
Published: September 2010

AbstractIn this work we measured at 298.2 K the viscosities η, the conductivities κ and the densities of the binary mixtures of 4NO2‐phenol with triethylamine (TEA) and of phenols with lower acidities with dibutylamine (DBA) or tributylamine (TBA). The metastable liquid TEA‐4NO2‐phenol mixtures exhibit a maximal viscosity as high as 8270 cpoise at a mole fraction xA = 0.71 of the acid. Around this mole fraction the mixtures are mainly constituted by conducting ions, as can be deduced from the product κη using Walden's rule as a first approximation. For the systems with the weaker phenols, for which ΔpKa is lower than 2.5, a marked part of the amine is present under the shape of non‐conducting entities and the viscosity maxima are much lower. Passing from the ethyl bases to the butyl bases does not trigger important changes in the height or in the position of the visocosity peaks. The ion concentrations become much smaller, but this effect is cancelled off by the rise of the molar volumes which enhances the viscosity. The drastic drop of the ion concentration in the mixtures when replacing the ethyl groups of the bases by butyl groups is partly due to the decrease of the dielectric constant of the solutions. This results from the diminution of the number of dipoles per unit volume.Not only the concentration of the conducting ions and their volume determine the viscosity of the mixtures but also the volume of the non‐conducting entities which are present into the solution. The enhancement of the viscosity when passing from dibutylamine to the less bulky triethylamine can be related to the difference in the shape of both molecules.
General models for helicenes
Authors: Navaza J. , Tsoucaris G. , Le Bas G. , Navaza A. , de Rango C. 
Published: September 2010

AbstractSeveral geometrical characteristics of 6‐, 7‐, 10‐, 11‐ helicene have been studied: accuracy of the binary axis, distribution of atoms over three helices, bond distances and angles, planarity and interplanar angles of benzene rings, existence of new planar groups. Two types of general models are suggested and discussed: the triple helix and the staircase model.
Analytical and TG, DIG and DTA studies of transition metal complexes of salicylic acid
Authors: Heda B. D. , Khadikar P. V. 
Published: September 2010

AbstractThe complexes of Fe(II), Zn(II) and VO(II) with salicylic acid have been prepared. Composition (ML2.2H2O) and structure of these complexes were established by elemental analyses and IR spectra. The thermal decomposition of these complexes using TG, DTG and DTA together with the analyses of intermediate products gave supporting evidence for the assigned structure. Thermal decomposition starts with dehydration and subsequently the anhydrous complex decomposes into corresponding metal oxide as the end product. Their dehydration temperature Increases with the increase in the coordinated water frequency. Thermal stability of the metal complexes increases in the order Fe>Zn>VO.
Solid ‐ liquid phase transfer catalysis using solid sodium hydroxide in preparative ethers synthesis
Authors: Jm. Dou H. , Delfort B. , Hassanaly P. , Gallo R. , Kister J. 
Published: September 2010

AbstractPreparative ethers synthesis can be performed using P.T.C. if solid sodium hydroxide is used as basic medium. In this case, side reactions ( eg: hydrolysis or elimination ) are avoided. Moreover, secondary disymetrical ethers can be synthezised starting from an alcohol and a secondary alkyl halide in acceptable yields.
A comparative study of the aggregation, rotational side‐chain isomerism and side‐chain/side‐chain interactions in the cyclic dipeptides c/Phe, Pip/ and c/Phe, (s)Pip/
Authors: Schrooten Rik , Joshi Satish , Anteunis Marc J. O. 
Published: September 2010

AbstractWe compare in this contribution the aggregation and the rotational side‐chain isomerism of the diastereomeric cyclodipeptides phenylalanine‐pipecolic acid (1, 2) with those previously observed1in the parent DKP's, containing the 4‐thiapipecolic acid moieties instead. Concomitantly with dimerisation (C8‐dimer) an increasing folding with concentration of the aromatic nucleus over the DKP‐ring is observed in aprotic solvents. The greater tendency for stacking in the cis‐isomer than in the trans‐isomer is thus reflected by a larger dimerisation capacity of the former. In the carbocyclic congeners the stabilisation of the folded form in the cis‐isomer is less pronounced than for the thia‐analog, thus confirming the surmise that an attractive interaction would occur when sulfur approaches a π‐system in space.
Selective reduction of α‐keto esters with organotin hydrides application to asymmetric syntheses
Authors: Rahm A. , Pereyre M. 
Published: September 2010

AbstractVrganotin hydrides selectively reduce the keto function group in α‐keto esters such as pyruvates or benzoylformates. Hydrostannation of (‐) menthyl benzoylformate with achiral reagents occurs with 5–20% asymmetric induction while the reaction of (−) 2 butyl‐diphenyltin hydride with ethyl benzoylformate only proceeds with a very low optical yield.
Kinetics and Mechanism of Oxidation of DL‐Proline by Manganic Sulphate in Acidic Medium
Authors: Ahmad Iftikhar , Odyek Olwa , Ashraf C. M. , Olal A. D. 
Published: September 2010

AbstractThe kinetics of oxidation of di‐proline by manganic sulphate in the acidic medium have been studied. The reaction is first order with respect to dl‐proline and manganic sulphate and inverse first order with respect to hydrogen ions. A reaction mechanism has been proposed.
Synthese von Heterocyclen unter Verwendung von Phosphoryliden
Authors: Bestmann Hans Jürgen 
Published: September 2010

AbstractEpoxides, nitril oxides and carbonyl compounds react with alkylidene triphenylphosphoranes by cycloaddition to PV‐heterocycles with a P‐O‐bond. The latter collapse according to a general reaction scheme, among others allowing a new interpretation of the mechanism of the Wittig reaction. Phosphacumulene and phosphaallene ylides are versatile reagents for the synthesis of heterocyclic compounds. A general ringclosure principle for the preparation of heterocycles is described. Cycloaddition onto the CC double bond in phosphacumulene ylides enables the synthesis of four, five and six membered heterocycles in a broad applicability.
Predictability of Proton Chemical Shifts in Polyether Carboxylic Acid Ionophores
Authors: And Frans Borremans , Anteunis Marc J. O. 
Published: September 2010

AbstractA statistical treatment of 342 chemical shifts from the 1H nmr spectra in chloroform of 17 polyether ionophores allows their prediction with reasonable accurracy (0.14 to 0.17 ppm). The predictions are based on increment values for vicinal gauche and more remote contributions. Some large deviations in shifts may be rationalized in terms of special effects such as “cavity”‐effect and complexation shifts.
Catalytic Properties of Synthetic MoS2 of Varying Surface Areas
Authors: Busetto Luigi , Iannibello Antonio , Pincolini Fabrizia , Trifiró Ferruccio 
Published: September 2010

AbstractMolybdenum sulfide catalysts of varying surface areas were prepared by thermal decomposition of MoS3 at 300, 350, 400, 450 and 500°. The surface areas has been found to be strongly dependent on the rate of heating suggesting a competition between the rate of nucleation and that of sintering of MoS2. The specific activities toward thiophene hydrodesulfuration and cyclohexene hydrogenation have been studied and their complementary trends have been attributed to the presence of at least two active centers. The catalytic properties and the variable surface area values found for the MoS3‐MoS2 system have been correlated to X‐Ray and analytical data.
Synthèse des 9‐, 10‐ et 11‐Fluoroacronycines
Authors: Smolders Robert René , Waefelaer Adolphe , Coomans Roland , Francart Didier , Hanuise Jean , Voglet Nicole 
Published: September 2010

AbstractA partir des 5‐, 6‐ et 7‐fluoroisatines, on décrit la synthèse des 9‐, 10‐ et 11‐fluoroacronycines via les 5‐, 6‐ et 7‐fluoro‐1,3‐dihydroxy‐10‐méthylacridan‐9‐ones.
Enzymatic “in Vitro” Reduction of Ketones: Part 9. Preparation of Pure (1S, 2S)‐2‐Chlorocyclohexanol
Authors: Sadozai S. K. , Merckx E. M. , van De Wal A. J. , Lemière G. L. , Esmans E. L. , Lepoivre J. A. , Alderweireldt F. C. 
Published: September 2010

AbstractThe enzymatic “in vitro” reduction of 2‐chlorocyclohexanone in a coupledsubstrate coenzyme recycling system (ketone ‐ ethanol ‐ NAD+ ‐ HLAD) delivers optically pure (1S, 2S)‐2‐chlorocyclohexanol. The optical purity is shown by 19F‐NMR of the (R)‐MTPA esters. The absolute configuration is mainly determined by ORD of the (2S)‐2‐chlorocyclohexanone.
Kinetics and Mechanism of the Ruthenium (III) Catalysed Oxidation of Some Aliphatic and Cyclic Ketones by Periodate Ion in Aqueous Alkaline Medium: A Novel Behaviour of Ruthenium (III)
Authors: Pati Subas C. , Panda Markandeswar 
Published: September 2010

AbstractKinetics of ruthenium (III) chloride catalysed oxidation of acetone, ethyl methyl ketone, isobutylmethyl ketone, pentan‐2‐one, cyclopentanone and cyclohexanone by sodium metaperiodate in aqueous alkaline medium at constant ionic strength is reported. The order with respect to [IO‐4] is found to be zero. The order with respect to [substrate] is unity for acetone, ethylmethyl ketone, isobutylmethyl ketone and cyclopentanone, whereas, pentan‐2‐one and cyclohexanone exhibit fractional dependence on substrate, in the entire range of substrate concentration studied. Strikingly, the order with resnect to [ruthenium (III)] is fractional in case of the ketones where substrate dependence is unity and Unity where the substrate dependence is fractional.The reaction rate increases linearly following a nearly unit dependence on [OH−] at lower concentration of alkali and levels off after a particular [OH−].The activation parameters have been evaluated. A suitable mechanism has been postulated and rate laws have been deduced.
On the mechanism of the rearrangement of N‐aryl α,α‐dichloroketimines with lithium aluminium hydride
Authors: De Kimpe Norbert , Verhé Roland , De Buyck Laurent , Schamp Niceas 
Published: September 2010

AbstractExperimental evidence is provided that the rearrangement of N‐aryl α,α‐dichloroketimines with lithium aluminium hydride in ether, observed as a competitive reaction during the stereospecific synthesis of cis‐aziridines, proceeds via consecutive transformation of α‐chloroaziridines into azirinium chlorides and α‐imidoylcarbenium ions, the latter being trapped by chloride anion to afford β‐chloroenamines, which furnish rearranged anilines on treatment with lithium aluminium hydride.
Structure Cristalline du Diméthyle‐1,10 Dihydro‐2,7 Tétraphyllinate de Diéthylaminoéthyle
Authors: Dupont L. , Dideberg O. , Sarlet P. 
Published: September 2010

AbstractThe crystal structure of 1,10‐dimethyl‐2,7‐dihydro‐diethylaminoethyl tetraphyllinate (C29H43N3O4) was determined. The compound shows interesting pharmacological properties in the cardiovascular area. Space group is orthorhombic P212121, Z=4, a=11.448(4), b=21.810(5), c=11.052(4)Å. The molecule has a 2α‐H, 3α‐H, 7α‐H, 15α‐H, 19α‐CH, 20β‐H configuration.
Transformations Catalytiques Des Hydrocarbures Aromatiques. I. Étude Thermodynamique du Processus de Disproportionation du Toluène
Authors: Oprea S. , Azzouz A. , Dumitriu E. , Constantinescu M. 
Published: September 2010

AbstractToluene disproportionation based a chemical model by thermodynamic way was studied. The distribution of reaction products was calculated by computer (Felix C‐256). Disproportionation of toluene was also carried out using NaY zeolites as catalysts, where the cation was exchanged with La3+, Ce3+, Co2+, Sr2+ ions and the composition of reaction mixture was determinated by gas chromatography. A good agreement between the conversions calculated by thermodynamic way and experimental data was noticed proving that the discussed model can be applied.
Alkaloids From Catharanthus Roseus 1H NMR Study of 20′S‐Deoxyvinblastine and its N‐2′ Borane Complex
Authors: De Bruyn André , Sleeckx Jozef , De Jonghe J. P. , Hannart J. 
Published: September 2010

AbstractThe 1H NMR spectra of 20′ S‐deoxyvinblastine and its N‐2′ borane complex have been unraveled. 2D δ‐J‐resolved NMR allowed to measure the isolated peaks in the overlapping patterns of the amine borane complex. Both compounds can now easily be discriminated on basis of 1H NMR data.
Étude Structurale Des Stilbènes III. Structures Par Diffraction de Rayons X de Quatre Dérivés E ou Z de L'α, β‐Diphénylacrylate de Méthyle
Authors: Tinant B. , Touillaux R. , Declercq J. P. , van Meerssche M. , Leroy G. , Weiler J. 
Published: September 2010

AbstractThe X‐Ray structures of four methyl α, β‐diphenylacrylate derivatives were solved by direct methods from diffractometer data. (I) (Z)‐methyl β‐p‐nitrophenyl‐α‐phenylacrylate, C16H13NO4, is monoclinic, P21/n, with α=8.296 (1), b=6.703(2), c=24.863(5)Å, β=96.25(1)°, V=1374.4(5)Å3, Z=4, (II) (Z)‐methyl α‐p‐nitrophenyl‐β‐phenylacrylate, C16H13NO4, is triclinic, P1, with α=14.233(3), b=10.048(2), c=9.907(2)Å, α=80.75(1), β=92.98(1), γ=92.48(2)°, V=1395.6(5)Å3, Z=4. (III) (E)‐methyl β‐p‐nitrophenyl‐α‐phenylacrylate, C16H13NO4, is monoclinic, Cc, with α=5.819(2), b=16.610(5), c=14.843(4)Å, β=96.14(2)°, V=1426.4(7)Å3, Z=4. (IV) (E)‐methyl β‐methyl‐β‐p‐nitrophenyl‐α‐phenylacrylate, C17H15NO4, is monoclinic, P21/α, with α=13.751 (4), b=11.145(3), c=10.956(4)Å, β=116.42(2)°, V=1503.7(8)Å3, Z=4.Molecular conformations are discussed and compared. The aromatic and ester substituents are generally twisted out of the ethylenic bond mean plane to avoid steric hindrance; only phenyl α in molecule II and ester group in III are coplanar with the CC bond. The C (arom.)‐CC bond angles are significantly greater than 120°.
Kinetics of N‐Formylation of Piperidine and Related Compounds
Authors: Maat L. , Peereboom M. 
Published: September 2010

AbstractThe kinetics of the N‐formylation of piperidine and 3‐methylpiperidine with chloral hydrate and 1,2,3,4‐tetrahydroisoquinoline with chloral in toluene, have been investigated. The reactions are first order in both reactants. The formylation of piperidine is faster than that of 1,2,3,4‐tetrahydroisoquinoline and somewhat slower than that of 3‐methylpiperidine.
Underpotential Adsorption of Mercury on Glassy Carbon
Authors: Kiekens P. , Van Broecke F. Den , Bogaert M. , Temmerman E. 
Published: September 2010

AbstractThe underpotential adsorption of mercury on glassy carbon has been studied. During electrodissolution, two stripping peaks are observed. The peak at more negative potentials corresponds to the oxidation of the bulk mercury, while the peak at more positive potentials results from the oxidation of mercury adsorbed on the surface of the electrode. The difference in peak potential between the adsorption (mono) layer peak and the bulk mercury peak has been related to the difference in work functions of deposit (mercury) and substrate (carbon).Mercury monolayer formation is found to be favoured at more negative potentials where the oxide surface film is reduced provided that interfering ions are absent, such as H+ or Cu(II) that can be reduced simultaneously with the mercury ions.
Preparation and Conformational Study Of Cis‐5‐methyl‐N1,N4‐diacetyl‐2‐piperazine‐N′‐methyl‐carboxamide
Authors: Anteunis Marc J. O. , Hosten Noël G. C. , Borremans Frans A. M. , Tavernier Dirk K. 
Published: September 2010

AbstractThe preparation of the racemic title compound is reported. An extensive 1H and 13C nmr study reveals the presence of four rotameric states about the two amide bonds (Table 4) and discloses that all four isomers possess almost identical twist‐boat ring shapes characterized by an endocyclic torsion angle along the Cα‐Cβ and Cδ‐Cϵ bond of ‐35±5° if an L‐configuration is considered.
Addition Radicalaire du Propanal à Divers Alcènes et Cyclènes: Aspects Stériques et Polaires
Authors: Tabbaa I. , Cazaux M. , Lalande R. 
Published: September 2010

AbstractFree radical addition of propanal to double bonds, initiated by benzoyl peroxide, mainly leads to two adducts, an aldehyde and a ketone, when the double bond has a methylene group; these results are explained in terms of polar effects in the free radical transfert reactions. When the double bond has no methylene group, only the ketonic adduct is obtained; the steric effects in the free radical addition step explain these results.
Catalytic Synergy in the Catalysis of N‐Ethyl Formamide Dehydration by Metal Oxides in Separate Phases
Authors: Ceckiewicz Stanislaw , Delmon Bernard 
Published: September 2010

AbstractMixtures of separately prepared oxides (of Mo, V, W, Bi, Sb, Sn) and BiPO4 exhibit a marked synergy in catalysis of the dehydration of N‐ethyl formamide in the presence of molecular oxygen, supporting the idea that a remote control of the active centres on one of the phases is exerted by the other phase via a special oxygen species.
Site Characterization on Reduced and on Sulfided Mo/Al2O3 Catalysis by Adsorption of Probe Molecules
Authors: Delgado E. , Fuentes G. A. , Hermann C. , Kunzmann G. , Knözinger H. 
Published: September 2010

AbstractCarbon monoxide adsorption on reduced and on sulfided Mo/Al2O3 was studied by gravimetry and low temperature IR spectroscopy. It is suggested that Mo4+‐ CO and Mo2+‐CO adsorption complexes are formed on H2‐reduced and on sulfided catalysts, respectively. The saturation coverage by CO in the temperature range between 125 K and 200 K is considered to provide a reasonable estimate of the density of cus Mo sites.
Structure Resonance Theory. Correlations of Electron Affinities and Polarographic Reduction Potentials of Polycyclic Aromatic Hydrocarbons
Authors: Shawali Admad S. , Elanadouli Baghat E. , Párkányi Cyril , Herndon William C. 
Published: September 2010

AbstractThe electron affinities and the polarographic half‐wave reduction potentials of aromatic hydrocarbons were correlated with the logarithms of the structure counts of the neutral molecules and the radical anions, ln SC(R) and ln SC(R°), respectively. Regioselectivity in the electrochemical reduction of these hydrocarbons is also discussed. The results obtained in this work indicate that the structure resonance theory can be successfully used for correlations of this type, and that effects due to the delocalization of π‐electrons in both the neutral and charged species are important factors in the electro‐chemical reduction of aromatic hydrocarbons.
Diacylmethylencyclopropane Als Zwischenstufen Einer Cyclopropansubstitution An Aminocyclopropanen
Authors: Vilamder E. 
Published: September 2010

AbstractThe rapid formation and the stability of cylopropylidene iminius intermediates 2 allow an easy nucleophilic substitution in aminocyclopropane derivatives 1. It is shown that disaceptor‐substituted methylenecyclopropanes 4a, being isoelectronic with 2, may occur as intermediates in nucleophilic cyclopropane substitution, too. Aminocyclopropyl‐substituted CH‐acidic compounds 1a proved to be suitable starting materials for this new type of substitution. The synthesis of compounds 1a is described. The amino moisty in 1a can be replaced by several nucleophiles such as carbanions, hydride, cyanide oder alkoxide. The poor stability of the diacceptor‐substituted methylenecyclopropane intermediate 4a turned out to impose a limitation on the new type of nucleophilic cyclopropane substitution. Decomposition of 4a without added nucleophile is investigated in the thermolysis of the aminocyclopropane derivatives 1a. Thereby, either a Favorski‐type ring opening is caused or methylene dihydrofuranes are formed. The latter result from a diacylmethylene cyclopropane intermediate 4a. Methods for the structural assignment of the starting materials 1a and of the products 5a are discussed giving an information about the steric course of the nucleophilic substitution.
Fractal Dimension and Exclusion Volume in Microporous Solids
Authors: Fripiat J. J. , van Damme H. 
Published: September 2010

AbstractMicroporous solids have domains unavailable for molecules with radii(r) larger than the statistical radius (ro) of the throats spread within the porous space. In addition, according to recent concepts, their highly corrugated internal surface could be characterized by a fractal dimension D which contains the entire information about the shape of the surface. In this contribution, it is shown, that unexpectedly either the monolayer content obtained by using the B.E.T. equation, as well as the inclusion volume, is proportional to (r−D‐r−D) for any value 2 < D < 3, if ro is considered as a function of D. This conclusion is obtained by probing microporous solids (X zeolite, microporous silica and ammonium phosphomolybdate) with various molecules which have radii in the range 3.8 < r < 6.7 Å.
Equilibrium Geometry and Proton Affinity of Vinyl Ethers and Sulphides by Ab Initio Calculations
Authors: Ösapay K. , Delhalle J. , Hevesi L. 
Published: September 2010

AbstractSTO‐3G equilibrium geometries for methoxy ethene, 1–1‐dimethoxy ethene, their thio analogs as well as for the corresponding C‐protonated species are reported. The carbenium ion stabilizing abilities of methoxy and thiomethoxy groups are discussed in terms of calculated proton affinities.
The Zero Point of Charge of Cassiterite
Authors: Taha Fouad , El‐Roudi A. M. , Saleh M. B. 
Published: September 2010

AbstractThe zero point of charge (ZPC) of cassiterite was investigated by measuring the electrophoretic mobility, solution equilibrium, and flotation response as a function of solution pH. The ZPC was shown to lie at pH 2. The potential determining ions for cassiterite are H+ and OH−.The effect of anionic and cationic collectors on the zeta potential of the mineral is studied. Mechanisms of charge development at the cassiterite ‐water interface are discussed. The preferential hydrolysis of surface ions or the adsorption, at the interface of the complexes formed in solution, appears to play an important part in establishing the surface charge.
Determination of Zirconium in Nodular Cast Iron by Instrumental Proton Activation Analysis
Authors: Goethals P. , Bosman B. , Vandecasteele C. 
Published: September 2010

AbstractAn instrumental method for the determination of zirconium in nodular cast iron using the 90Zr(p,n) 90Nb reaction was developed. The 2319 keV γ‐rays of 90Nb (t1/2=14.6 h) were measured with a Ge(Li) detector with 4 cm of lead interposed between the sample and the detector.For concentrations ranging from 200 to 1200 μg.g−1, the experimental standard deviation ranges from 2 to 5%. The results are in good agreement with those obtained by ICP‐emission spectrometry and were used to establish a linear calibration graph for the determination of zirconium in cast iron by X‐ray fluorescence spectrometry (XRF) on the Zr Kα line.
Gnetins in Welwitschia
Authors: Lins Arlete P. , Yoshida Massayoshi , Gottlieb Otto R. , Gottlieb Hugo E. , Kubitzki Klaus 
Published: September 2010

AbstractA wood sample of Welwitschia mirabilis is reported to contain nerolidol and para‐hydroxybenzaldehyde, besides two dehydroresveratrol dimers gnetins F and G and two dehydroresveratrol trimers gnetins H and I for which structures are proposed. Other oxidative resveratrol oligomers, gnetins A, B, C, D and E, have been isolated previously from three Amazonian Gnetum species. These facts provide welcome evidence for the discussion of relationships within the Gnetatae.