bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on Dissociation Equilibria in Water + Dimethylsulphoxide Mixtures and Free Energies of Transfer of Hydrogen Ions
Authors: Deb C. C. , Hazra D. K. , Lahiri S. C. 
Published: September 2010

AbstractThe dissociation constants for the ‘isoelectric’ reactions of the type AH+ · A + H+ (where A = 2,2′‐bipyridine or 1,10‐phenanthroline) have been determined in water + dimethylsulphoxide mixtures (0–90.81 wt% of DMSO) pH‐metrically (using glass and calomel electrodes) and spectrophotometrically. The free energies of transfer of the H+ ion have been calculated. The ΔGto (H+) values have been found to be increasingly negative up to 80 wt% organic solvent indicating that basicity is maximum in this region beyond which the basicity decreases.
Ag(I) ‐ Catalysed Oxidation of Diacetone Alcohol by ce(iv) in H2SO4 Medium
Authors: Nageswar Rao K. , Sondu S. , Sethuram B. , Navaneeth Rao T. 
Published: September 2010

AbstractThe rate of oxidation of diacetone alcohol (DAA) by Ce(IV) in H2SO4 medium increases significantly in the presence of Ag+ ions. The order with respect to [Ce(IV)] is strictly one both in the presence and absence of Ag(I) while the order in [DAA] is fractional in the presence of Ag(I). A mechanism involving the formation of (Ag(I)‐substrate) adduct in the initial step, followed by the reaction with Ce(IV) in the rate determining step to form (Ag(II)‐substrate) adduct which subsequently undergoes internal oxidation to yield the products has been suggested to explain the results. Thermodynamic parameters both in the presence and absence of Ag(I) are also presented and discussed.
Études Structurales En Série Helicenique II. Structure Du (Hydroxy‐1 Éthyl)‐1 Hexahelicene
Authors: van Meerssche M. , Declercq J. P. , Germain G. , Soubrier‐Payen B. , Lindner H. J. , Kitschke Brigitte 
Published: September 2010

AbstractThe crystal and molecular structure of the title compound has been determined by X‐ray diffractometry. The crystal are orthorhombic, space group P212121 with four molecules in the unit cell with dimensions a = 8.541(3), b = 14.100(4), c = 15.812(5)Å. The analysis shows that the compound is the (dl) PR‐MS isomer.
Étude De La Réactivité De Composes Enaminocarbonyles Vis‐À‐Vis De La 1‐Phénylpyrazolidine‐3,5‐Dione.
Authors: Maquestiau A. , Vanden Eynde J.‐J. 
Published: September 2010

AbstractIn acetic acid at room temperature, 3‐amino‐1‐phenyl‐2‐buten‐1‐one, 4‐amino‐3‐penten‐2‐one, various 3‐aminocrotonic esters and amides react with 1‐phenylpyrazolidin‐3,5‐dione to yield compounds resulting from the elimination of ammonia between the two precursors and the so obtained derivatives cyclize on heating to pyrano [2,3‐c] pyrazoles. The rates of these reactions are measured by 1H NMR spectroscopy and mechanistic interpretations are proposed.Under the same experimental conditions, β‐dicarbonyl compounds are less reactive than the enaminocarbonyl analogues.
Iridoids. Alternative Synthesis of a Key Intermediate for the Synthesis of (±)‐Mussaenoside and (±)‐8‐Epiloganin from 2‐Methoxycarbonyl Tricyclo|3.3.0.02,8|Octanone‐3
Authors: Callant P. , De Wilde H. , Storme P. , Vandewalle M. 
Published: September 2010

AbstractStarting from 2‐methoxycarbonyl tricyclo|3.3.0.02,8|octanone‐3 (5b) am alternative synthesis of 2‐methoxycarbonyl‐cis‐bicyclo|3.3.0|‐2‐octenone‐6 (9) is reported. 9 has previously been used as an intermediate for (±)‐mussaenoside (3) and (±)‐8‐epiloganin (4).
New Prototropic Processes in the Synthesis of Heterocyclic Compounds
Authors: Grigg R. 
Published: September 2010

AbstractXYZH systems are considered in general terms and divided into four classes according to the number of constituent atoms that possess lone pair electrons. Those systems in which the central Y atom possesses a lone pair are shown to be capable of participating in formal 1,2‐H shifts generating 1,3‐dipolar species. The scope, regiochemistry and stereochemistry of the cycloadditions of these 1,3‐dipoles is discussed including the relevance of these processes to the biochemistry of pyridoxal enzymes.
NIMO/Al2O3 Catalysts. NI and MO Concentrations Effect. A Comparative Study of Pyridine HDN and Thiophene HDS Reactions on Reduced and Sulfided Catalysts
Authors: Ledoux H. J. , Agostini G. , Benazouz R. , Michaux O. 
Published: September 2010

AbstractThe Ni and Mo concentrations effect on the pyridine HDN and thiophene HDS under normal H2 pressure, on reduced or sulfided classical NiMo/Al2O3 has been studied by comparison of activities and by simultaneous analysis of the selectivity in different products. If the expected promoting effect of Ni for the HDS reaction has been found, the best catalyst for HDN was the pure Mo/Al2O3. It has also been found that the sulfided Mo catalyst is a better hydrogenating system than the reduced oxidic form and the sulfided Ni promoted catalysts. An attemp to explain the promoting effect of Ni on Mo based catalysts is given.
Unsupported MoS2 and WS2 Model Catalysts: Influence of Textural Properties on Hydrodesulfurization and Hydrogenation Activities
Authors: Fréty R. , Breysse M. , Lacroix M. , Vrinat M. 
Published: September 2010

AbstractUnsupported MoS2 (WS2) were prepared by decomposition of ammonium thio‐salts, under a flow of H2 + 15 % H2S at 673 K.Samples with surface area ranging from 5 to 80 m2g−1 were tested in hydro‐desulfurization of dibenzothiophene and hydrogenation of biphenyl, at moderate temperature (523 ‐ 573 K) and medium high pressure (pT = 22.5 105Pa) conditions.The activity, measured at the pseudo steady state, expressed in mole g−1 sec−1 was found directly proportional to the surface area of the tested catalysts, for both reactions and both types of catalysts.Therefore the preceding reactions appear as “texture insensitive” for both WS2 and MoS2 catalysts.
Unsupported Ni‐mo Sulfide Catalysts: Relation Between the HDS and Hydrogenation Activities and Some Structural Properties
Authors: Gachet C. , Paulus R. , De Mourgues L. , Durand C. , Toulhoat H. 
Published: September 2010

AbstractA series of unsupported sulfide catalysts containing nickel and molybdenum (with variable atomic ratio a Ni/Ni + Mo) was prepared using a variant of the H.S.P. method which promotes an “intimate contact” between the metallic ions. These catalysts show good activities in the dibenzothiophene hydrodesulfurization (under atmospheric or high pressure) and in the biphenyl hydrogenation. For the two reactions, the maximum of synergy is observed for a about 0.7.X‐ray diffraction shows that for a < 0.3, only the MoS2 type phase is detected (before and after catalytic test). For higher values of a, nickel sulfide initially present under the NiS2 and NiSβ phases form, is converted into the Ni3S2 phase by catalytic working.The variations, in terms of a, of the specific area, of the stoichiometric ratio S/Ni + Mo' of the c parameter of the MoS2 type phase, of the TPR spectra shape, show the existence of a mixed phase “Mo ‐ Ni ‐ S” of the same crystallo‐graphic type than MoS2. The presence of this phase would induce an increase of the HDS and hydrogenation properties of the catalyst without explaining the position of the synergy maximum.
IR and AEM Evidence for the Edge Location of the Promoter Atoms in Co‐Mo‐S Type Structures
Authors: Topsøe Nan‐Yu , Topsøe Henrik , Sørensen Ole , Clausen Bjerne S. , Candia Roberto 
Published: September 2010

AbstractIn the present paper, we will discuss recent results which show that the catalytically active Co‐Mo‐S or Ni‐Mo‐S structures consist of Co or Ni atoms at the edges of MoS2. The evidence has been observed by ir studies of NO adsorption and analytical electron microscopy (AEM) investigation of alumina supported and unsupported Co‐Mo and Ni‐Mo hydrodesulfurization catalysts. These studies have also been extended to catalysts sulfided at elevated temperatures. By combining the ir and AEM results with results from Mössbauer emission spectroscopy (MES) and EXAFS, it is found that in order to achieve a large promotion of the HDS activity one must have both a high coverage of the MoS2edges and a high MoS2edge dispersion. It is seen that one advantage of using alumina supports is the possibility of preparing MoS2with high edge dispersion.
Temperature Programmed Sulfiding of CoO/MoO3/γ‐Al2O3 Catalysts
Authors: Scheffer B. , De Jonge J. C. M. , Arnoldy P. , Moulijn J. A. 
Published: September 2010

AbstractThe sulfiding of CoO/MoO3/γ‐Al2O3 catalysts was studied by a technique called Temperature Programmed Sulfiding (TPS). Cobalt loading, calcination temperature and pretreatment were varied.CoO/MoO3/γ‐Al2O3 catalysts sulfide at lower temperatures than model compounds such as CoO, MoO3 and CoMoO4 because of the higher dispersion in the catalysts. Sulfiding of Mo in CoO/MoO3/γ‐Al2O3 catalysts is dominated by O‐S exchange, reduction of Mo is due to Mo‐S bond rupture followed by reduction of elemental sulfur, in the same way as occurs in MoO3/γ‐Al2O3 catalysts.For Co in CoO/MoO3/γ‐Al2O3 catalysts the sulfiding pattern depends strongly on the calcination temperature: low calcination temperatures (785 K) lead to catalysts which show sulfiding of Co species in the same temperature range as Mo, and an increase in the reduction rate of elemental sulfur formed by reduction of Mo oxysulfides.Sulfiding of CoO/MoO3/γ‐Al2O3 leads to Co species which are stabilized and more disperse than those in sulfided CoO/MoO/γ‐Al2O3 catalysts. Calcination temperatures higher than 785 K cause a decrease of the amount of easily sulfidable Co species, and an increase in the amount of Co which sulfides at high temperature (1000 K).As was found for MoO3/γ‐Al2O3 and CoO/γ‐Al2O3 catalysts the “water content” of CoO/MoO/γ‐Al2O3 catalysts has an influence on the sulfiding patterns: “wet” catalysts (containing up to 6% water) with low Co loading sulfide at lower temperature than dried catalysts. Sulfiding (in TPS) proceeds at a higher rate than reduction by H2 (in TPR).
Effect of Sulfiding Temperature on Activity and Structures of CO‐MO/AL2O3 Catalysts. ii
Authors: Candia Roberto , Sørensen Ole , Villadsen JØRgen , Topsøe Nan‐Yu , Clausen Bjerne S. , Topsøe Henrik 
Published: September 2010

AbstractThe changes, which take place in the structural and catalytic properties of Co‐Mo/Al2O3 catalysts sulfided at different temperatures, have been elucidated by means of high resolution electron microscopy (HREM), ir, XRD, and chemisorption of oxygen. It was observed that high temperature sulfiding induces a growth in the Co‐Mo‐S crystals which are MoS2‐like with Co occupying edge positions. For all the catalysts, Co‐Mo‐S was found to be the most important feature in determining the HDS activity and it was found that the changes, which occur with the HDS activity, can be explained in terms of the changes in the total MoS2 edge area and its Co coverage. When saturation edge coverage is exceeded, segregation of excess Co in the form of Co9S8 takes place. Differences in the hydrogenation activity can be explained in terms of variations in the relative number of promoted vs. unpromoted MoS2 edge sites. Upon increasing the sulfiding temperature, the nature of the Co‐Mo‐S structure changes from a low temperature form (Type I Co‐Mo‐S) to a high temperature form (Type II Co‐Mo‐S). It is suggested that support interactions are less important for Type II Co‐Mo‐S than for Type I.
Influence of Sulfidation Temperature on the Dispersion and Activity of Cobalt‐Molybdenum Catalysts Supported on γ‐Alumina
Authors: Prada Silvy R. , Beuken J. M. , Bertrand P. , Hodnett B. K. , Delannay F. , Delmon B. 
Published: September 2010

AbstractA commercial cobalt‐molybdenum catalyst supported on γ‐alumina was activated by reduction‐sulfidation under 15% H2S in H2 in the temperature range 573 to 1073K. Optimum hydrodesulfurization activity was achieved after activation between 673 and 803K. At lower temperatures lower activity was observed and X‐ray photoelectron spectroscopy indicated that this was due to incomplete sulfidation of cobalt and molybdenum. Sintering of the supported phase, which occured after activation above 800K, was measured by high resolution electron microscopy, ion scattering spectroscopy and dynamic oxygen chemisorption. The hydrodesulfurization activity varied in the same proportion as the surface area of the MoS2‐like crystallites. It was concluded that the number of active sites per unit surface area of supported phase and the intrinsic activity of these sites for hydrodesulfurization did not change during activation above 800K.
Kinetic Models for the Hydrogenolysis of Thiophene. A Comparison of Hougen‐Watson Models with Fixed and Interconverting Sites for Hydrogenolysis and Hydrogenation
Authors: van Parys I. , Froment G. F. , Delmon B. 
Published: September 2010

AbstractA Hougen‐Watson model with interconverting sites (H.W.‐I.S.) has been formulated to account for the influence of H2 and H2S on the number of active sites. The model assumes that the ratio of the concentration of active sites for hydrogenolysis and hydrogenation depends upon the ratio of the partial pressures of H2 and H2S. Compared to the Hougen‐Watson model with a fixed number of active sites (H.W.‐F.S.), this H.W.‐I.S. model is less satisfactory for low partial pressures of H2S. For higher Ps/PH ratios, however, the H.W.‐I.S. model can compete with the H.W.‐F.S. model. These results suggest that only a fraction of the adsorbed sulfur is converted into an active site for hydrogenation and that most of the adsorbed sulfur is desorbed as H2S, leaving an active site for hydrogenolysis on the catalyst surface.
Étude de la Relaxation Diélectrique du Dmso
Authors: Elie Volf 
Published: September 2010

AbstractAu cours de ce travail nous avons étudié la dispersion diélectrique du DMSO entre 1 et 15 360 megaHz et ceci pour des températures comprises entre 20 et 60°C.Le DMSO présente une dispersion diélectrique proche d'un corps possédant une faible répartition des temps de relaxation, et le type de représentation est celui d'un diagramme de Cole et Cole avec des coefficients de dispersion inférieurs à 0,02.Les temps de relaxation diélectrique sont de l'ordre de 10−11s et les calculs de ΔH, ΔF, ΔS de rotation dipolaire confirme que le DMSO est un liquide peu associé avec un facteur de correlation de Kirkwood proche de 1,10.
Kinetics Study of Adsorption of CO2 on ZNCO2O4
Authors: Reyes Patricio A. , Plaza De Los Reyes Jorge F. 
Published: September 2010

AbstractThe kinetics of chemisorption of CO2 on ZnCo2O4 in a temperature range 373–423K, and pressure varying from 5 to 21 mmHg has been studied.A kinetic law that could fit adequately the experimental data was investigated, being this the Elovich equation. The activation energy, determined by Arrhenius law, was also calculated.
Dipolar Study of Complexes Between Trialkylamines and Several Molecules of Carboxylic Acids
Authors: Kapuku F. , Huyskens P. L. 
Published: September 2010

AbstractThe dipole moment μ of carboxylic acid‐trialkylamine adducts containing more than one acid molecule in cyclohexane solutions and in the pure acid is significantly larger than the moment of the one:one complex μab. This is due to a larger value of the proton transfer constant for these complexes. At a given dielectric constant (ϵ = 3 and ϵ = 4), the increase of the proton transfer constant is especially important going from the ab to the a2b complexes, the further increase of the constant when adding still more acid molecules being rather small. This is also observed for the volume contraction of the binary mixtures carboxylic acids‐trialkylamine.The proton transfer constant of the aib complexes also depends on the dielectric constant of the medium and on the nature of the base but seems to remain approximately the same for all the acids considered. At ϵ = 3, K° is of the order of 0.58 for the complexes with triethylamine and 0.67 for tributylamine. At ϵ = 4, the figures are 0.76 and 0.87.
Charge Transfer Complexes of Nitrones, III1 π‐π Molecular Complexes of 2H‐Pyrrole‐N‐Oxides and One Isoindole‐N‐Oxide
Authors: Nour El‐Din Ahmed M. , Döpp Dietrich 
Published: September 2010

AbstractMolecular complexes between four 2H‐pyrrole‐N‐oxides as well as one isoin‐dole‐N‐oxide and 2,3‐dichloro‐5, 6‐dicyanobenzoquinone, tetracyanoethylene and tetracyanoquinodimethane in dichloromethane at 25°C have been studied spectro‐photometrically in the visible region. Stability constants and transition energies of the charge transfer complexes have been determined. At higher temperature (35°C) decomposition of the complexes has been observed. The ionization potentials of the donors were calculated from the energy of charge transfer transitions. The results show a strong positional effect and addivity effect of the substitution and conjugation with the azomethine‐N‐oxide group.
Acétonylation Aromatique Homolytique
Authors: Gardrat C. 
Published: September 2010

AbstractTreatment of monosubstituted benzene derivatives with acetone and manganese (III) acetate in acetic acid gave rise to products of homolytic aromatic substitution in fairly good yields and high purity except for toluene, Isomer distribution, relative rates and partial rate factors were determined for toluene, anisole, chlorobenzene, bromobenzene and benzonitrile. A Hammett plot of the logarithm of the partial rate factors for meta and para positions vs. σ‐constants gave a slope ρ of −1.74 ± 0.40 (confidence interval at the level 95°). When using σ+‐constants the slope becomes ρ+ = −1.25 ± 0.36. The negative values of ρ and ρ+ indicated that the acetonyl radical has an appreciable electrophilic character.
N‐Nitrosamines from the Reaction of Sulfamoyl Chlorides with Sodium Nitrite
Authors: Warner John C. , Nakajima Masayuki , Anselme Jean‐Pierre 
Published: September 2010

AbstractN,N‐Dialkylsulfamoyl chlorides react smoothly with sodium nitrite in acetonitrile to afford the corresponding N‐nitrosamines in nearly quantitative yields.
Petrosin‐A and ‐B, Two New Bis‐Quinolizidine Alkaloids from the Sponge Petrosia Seriata(1)
Authors: Braekman J. C. , Daloze D. , Defay N. , Zimmermann D. 
Published: September 2010

AbstractThis paper describes the structure determinations of two new ichthyotoxic bis‐quinolizidine alkaloids from the marine sponge Petrosia seriata. The structural elucidations are mostly based on homonuclear 2D‐1H NMR experiments.
Nitration of Phenols by Clay‐Supported Ferric Nitrate
Authors: Cornlis A. , Laszlo P. , Pennetreau P. 
Published: September 2010

Abstract“Clayfen”, a reactive form of ferric nitrate stabilized by adsorption unto an acidic K 10 clay, is an efficient and selective nitrating agent of phenols, under very mild conditions. It leads specifically to mononitration, with high regioselectivities. These characteristics, coupled with its low cost, ease of preparation and the simplicity of experimental procedures, make “clayfen” an attractive nitrating reagent.
N.M.R. Study of Molecular Interactions between Xenon and Crown Ethers
Authors: Claessens M. , Fabre O. , Zimmermann D. , Reisse J. 
Published: September 2010

Abstract129Xe N.M.R. has been used to investigate intermolecular interactions between xenon and different crown ethers. Chemical shifts of this isotope measured in chloroform solutions containing various amounts of glymes and crown ethers show that the behaviour of the cyclic molecules is qualitatively very different from their linear analogues. Experimental data are interpreted in the frame of a 2− and 3‐site model developed for linear and cyclic ethers respectively. Our results support the existence of a loosely bound host‐guest pair between xenon and crown ethers characterized by an equilibrium constant K which appears to be independent of the ring size of the crown ether molecules.
Iridoids. Asymmetric Synthesis Via Enantiomeric Separation of the Mono Methylester of 2, 3‐DI‐Endo‐Hydroxycarbonyl‐5‐Norbornene
Authors: Storme P. , Quaeghebeur L. , Vandewalle M. 
Published: September 2010

AbstractEnantiomeric separation of racemic mono methylester of the known 2, 3‐di‐endo‐hydroxycarbonyl‐5‐norbornene (2) is possible via the ephedrine salts. Both enantiomers can be converted into 2, R‐endo‐methoxycarbonyl‐3, S‐endo‐hydroxymethyl‐5‐norbornene (−)−4, which is a suitable intermediate for asymmetric synthesis of iridoids.
Intramolecular Diels‐Alder Reaction with Furan‐Diene. 1. A Novel Entry to the BCD‐Ring System of 11‐Ketosteroids
Authors: van Royen Luc A. , Mijngheer Roelant , De Clercq Pierre J. 
Published: September 2010

AbstractA novel approach for the synthesis of the BCD‐ring system in steroids is described. The sequence centers about the intramolecular Diels‐Alder reaction of furan 15, which, depending on the reaction conditions, leads predominantly to adduct 26 (kinetic control) or 27 (thermodynamic control). The precursor 15 is obtained from enol ether 2, prepared via dissolved metal reduction of 5. Only in reduced adduct 34 is the oxygen bridge opened without concomitant epimerization at C‐14. The synthesis of other dienophiles (17, 19, 22 and 25) and their Diels‐Alder reactivity is discussed.
The Oxidation State of Cobalt and Its Coordination State in 3‐(4,5‐Dimethyl‐2‐Thiazolylazo)‐2,6‐Diaminopyridine Chelate
Authors: Gallo B. , Santiago C. , Arnaiz A. R. 
Published: September 2010

Abstract3‐(4,5‐dimethyl‐2‐thiazolylazo)‐2,6‐diaminopyridine has been synthesized for the first time in our laboratory. It forms a stable coloured complex with cobalt, which is a sensitive reagent for the spectrophotometric determination.The stability constant and the extraction behavior of the chelate, and its metal‐to‐ligand ratio have been determined previously. In the present work the CoL2n+ complex is characterized in the solid state by means of EPR, IR and UV/visible spectroscopy, and measurement of the magnetic susceptibility. Elemental analysis has also been performed.
X‐ray Diffraction Study of (±)‐5α‐ [2′‐Hydroxy‐l'‐Methoxycarbonyl‐2'‐(3″,4″,5″‐Trimethoxyphenyl) Ethyl)‐4α‐(3″‐4″‐Methylenedioxyphenyl)‐2α‐Phenyl‐1,3‐Dioxane
Authors: Piccinni‐Leopardi C. , Declercq J. P. , Germain G. , van Meerssche M. , van Der Eycken J. , De Clercq P. , Vandewalle M. 
Published: September 2010

AbstractC30H32O10, monoclinic, P21/c, a = 12.932(5), b = 9.670(6), c = 23.276(13)Å, β = 103.87(4), ν = 2825.9(25)Å3, Mr = 552.58, Z = 4, Dx = 1.30 mg cm−3. The structure was solved by direct methods (MULTAN 80) and refined (SHELX 76) to a final R value of 0.056 for 2344 observed reflections.The dioxane ring has a chair conformation. On this ring, two substituents, the phenyl and the methylenedioxyphenyl groups, are in equatorial positions while the substituted ethyl fragment is axial.
A Note on the Crystal Structure of 9,10‐ Anthraquinone
Authors: Lenstra A. T. H. , van Loock J. F. J. 
Published: September 2010

AbstractC14H8O2; Mr = 208.1, monoclinic, P21/c, a = 3.956(3), b = 7.866(3), c = 15.766(4) Å, α = 102.7(3)°, Z = 2, V = 478.5 Å3, F(000) = 216, Dx = 1.445 Mg m−3, Mo‐radiation, λ = 0.71073 Å, μ = 0.104 mm−1, crystal size 0.15 × 0.2 × 0.15mm., R = 0.106, Rw = 0.102 for 718 reflections with I > 3 σ (I) out of 1024 independent measurements at room temperature. The redetermination confirms geometrical features given by previous investigations. The poor fit between observations and model could be shown not to be caused by extinction effects.
Étude de la Décarbonylation du 1‐Acétylimidazole et du 1‐Acétylpyrazole Ionises
Authors: Maquestiau A. , Tommasetti A. , Pedregal‐Freire C. , Elguero J. , Flammang R. 
Published: September 2010

AbstractCollisionally activated dissociations (CAD) spectra have been used to investigate the structures of ions produced by decarbonylation of 1‐acetylimidazole [1] and acetylpyrazole [12] ionized by electron impact. The results are best explained by the formation of non classical methylene‐azolium ions. The loss of carbon dioxide from l‐methoxycarbonylimidazole [7] does not produce these ions but instead leads to ionized C‐methyl‐2(or 4)H‐imidazole. A mixture of structures is produced by electron impact induced fragmentation (loss of C2H4) of 1‐(2‐hydroxypropyl)imidazole [9]