bluuebunny/crossref_metadata_2025 huggingface dataset:
Réduction catalytique de cétones α,β-éthyléniques à température modérée par
Authors: Beaupere D. , Bauer P. , Uzan R.
Published: May 2006

The use of the catalyst [Formula: see text] in the reduction of the ethylenic system of styryl ketones by 1-phenylethanol permits the hydrogenation reaction to proceed at 50 °C. Some substituent effects in the α,β-unsaturated ketones were demonstrated at this temperature. These showed an increase in the initial rate of reduction for electron-attracting groups and the inverse effect for electron-donating groups. The observation of a relation between the electrochemical reduction potential of these ketones and their rate of hydrogenation suggests a transfer of hydrogen to the ketone by a hydride ion intermediate. [Journal translation]
α,β-Epoxy sulfoxides and sulfones. Synthesis and some reactions
Authors: Durst Tony , Tin Kam-Chung , Reinach-Hirtzbach Francois De , Decesare John M. , Ryan M. Dominic
Published: May 2006

A number of α,β-epoxy sulfoxides and epoxy sulfones have been prepared via cyclization of α-chloro-β-hydroxy sulfoxides or phase-transfer catalyzed reaction between α-chloroalkyl sulfones and carbonyl compounds. Thermal and acid-catalyzed rearrangement of these epoxides resulted in migration of sulfinyl or sulfonyl groups to form β-carbonyl sulfoxides or sulfones. Upon treatment of the epoxy sulfones with MgBr2 in ether, α-bromocarbonyl compounds were obtained in excellent yield. The reaction of epoxy sulfones with nucleophiles was also briefly investigated.
Stereochemical equilibration of the lithium derivatives of 1,2-diols
Authors: Slemon Clarke E. , Yates Peter
Published: May 2006

The dilithium derivatives of the ditertiary 1,2-diols, cis- and trans-1,2-dimethyl-1,2-cyclo-hexanediol, fail to undergo base-induced stereochemical equilibration under conditions that lead to such equilibration with the dilithium derivatives of the disecondary 1,2-diols, cis- and trans-1,2-cyclohexanediol. This casts doubt on the proposal that the latter equilibration proceeds by carbon–carbon bond cleavage of the dialkoxide to give a diketyl intermediate. It is highly probable that it involves oxidation–reduction as established by Doering in the case of monohydric alcohols. Examination of steroidal secondary-tertiary 1,2-diols under similar conditions shows that such systems can epimerize at both carbinol centres; this is interpreted in terms of sequential oxidation, α-ketol rearrangement, and reduction.
Etude par spectrométrie infrarouge de l'action de solvants aprotiques sur l'association ester–eau et ester–Ba2+. Discussion du rôle catalytique du solvant et de l'ion Ba2+ dans l'hydrolyse alcaline du propionate de methyle
Authors: Narvor Anne Le , Saumagne Pierre
Published: May 2006

The ir spectra of mixtures of methyl propionate/water and methyl propionate/Ba2+ in dimethylsulfoxide and in acetonitrile have been recorded in the region of the νCO mode of the ester. Evidence is presented to indicate the presence of different types of complexes; their concentration was determined as a function of the composition of the medium. The spectroscopic results are compared to those from the kinetics of the alkaline hydrolysis in the same conditions. It is demonstrated that the orbital control explains the experimental results better than does the charge density on the carbon of the carbonyl group. [Journal translation]
A stereoselective synthesis of sucrose. Part II. Theoretical and chemical considerations
Authors: Fraser-Reid Bert , Iley David Erle
Published: May 2006

Under the agency of an iodonium ion, the tertiary anomeric hydroxyl of tetraacetyl fructofuranose adds stereoselectively in a 1,4 sense, to a pyranoid 4,6-O-benzylidenated conjugated diene receptor. The resulting disaccharide, isolated in 45% yield, is an hex-2-enopyranoside possessing an allylic primary iodide which can be oxidised to an aldehyde either directly or after hydrolysis to the allylic primary alcohol. The aldehyde is decarbonylated and the unsubstituted hex-2-enopyranoside formed undergoes hydroxylation giving exclusively the manno-diol. After protecting the equatorial hydroxyl as the benzoate ester, the axial 2-hydroxyl group is inverted via oxidation followed by borohydride reduction. Acetylation gives the known 4,6-O-benzylidene hexaacetyl derivative of sucrose, which is identified by mixture melting point.
Molecular orbitals from group orbitals. IX. The problem of hybrid lone pairs
Authors: Kost Daniel , Schlegel H. Bernhard , Mitchell David John , Wolfe Saul
Published: May 2006

The quantitative PMO analysis of the ab initio wavefunction of a molecule A—B is based upon a partitioning of the Fock matrix elements of this wavefunction to obtain the fragments A and B, followed by computation of the stabilizing and destabilizing orbital interactions between the orbitals of these fragments that contribute to the HOMO of A—B. However, when one or both of the fragments is NH2 or a congeneric species, neither the 3a1 nor the 1b1 orbital of this fragment is appropriate for overlap with the second fragment, and the PMO analysis cannot be performed. A solution to this problem is proposed, and has been tested by application to various conformational properties of methylamine.
Etude des complexes du tungsténe(VI) dans l'excès de acide malique
Authors: Cervilla Antonio , Beltran Aurelio , Beltran José
Published: May 2006

The complex formation between W(VI) and malic acid (H2M) has been investigated polarimetrically in excess malic acid. The formation of three different complexes is confirmed. The stoichiometry and the degree of condensation of these complexes can vary depending on the acidity. Furthermore, the results obtained show that both tartaric and malic acids behave similarly in forming complexes with W(VI). The formation constant of the complex [O2W(OH)2(M2)]4− has been determined by two different methods.
Synthèse et étude du rearrangement des diazoles-1,3: alkyl-1 alkylthio-2 (allylthio, arylthio, cycloalkylthio) imidazoles. Partie I. Synthèse et études physicochimiques
Authors: Kister Jacky , Assef Georges , Mille Gilbert , Metzger Jacques
Published: May 2006

The synthesis and the [Formula: see text] rearrangement of thioethers in the N- and S-substituted imidazolic series have been studied (60 compounds). The physicochemical studies of the thioethers and mercapto compounds, catalysts of the rearrangement, and of the eventual hydrolysis products have been carried out and the kinetics of rearrangement have been examined at several temperatures. The rearrangement and hydrolysis results are compared with those of 1-alkyl-2-methylthio-Δ-2-imidazolines and 1-alkyl-2-methylthio-Δ-2-tetrahydropyrimidines and the electronic and steric effects are discussed. In this first part the synthetic aspect and physicochemicals results are presented.
Synthèse et étude du réarrangement des diazoles-1,3: alkyl-1 alkylthio-2 (allylthio, arylthio, cycloalkylthio) imidazoles. Partie II. Réarrangement et réactions parasites
Authors: Kister Jacky , Assef Georges , Mille Gilbert , Metzger Jacques
Published: May 2006

The kinetics of the [Formula: see text] rearrangement reaction for a series of 1-alkyl-2-alkylthio (or allylthio, arylthio, cycloalkylthio) imidazoles has been studied at various temperatures. The rearrangement and hydrolysis results have been compared with those of 1-alkyl-2-methylthio-Δ-2-imidazolines and 1-alkyl-2-methylthio-Δ-2-tetrahydropyrimidines. Electronic and steric effects are discussed and a parallel between pKa and rearrangement is proposed. The limit of this parallel is either a structural effect such as direct (ortho effect) or indirect (cycle deformation) steric interactions or geometric modifications of the heterocycles studied (five- or six-membered cycles). All these results permitted the coherent choice of the amplification compound of a nonconventional photographic process.
Cyclization of the 4-cyanobutyl radical
Authors: Griller David , Schmid Peter , Ingold Keith U.
Published: May 2006

The rate constant for the irreversible cyclization of the 4-cyanobutyl radical to the cyclopentiminyl radical, [Formula: see text]has been measured from −52 to 12 °C by kinetic epr spectroscopy. The temperature dependence of this rate constant can be represented by,[Formula: see text]where θ = 2.3RT kcal/mol. This rearrangement is somewhat slower than the analogous cyclizations of the 5-hexenyl and 5-hexynyl radicals.
Photolyse du propène et du méthyl-2-butène-2 vers 174 et à 163 nm
Authors: Collin Guy J. , Deslauriers Hélène , Deschênes Jovette
Published: May 2006

We have studied the 163 nm photolysis of propene and of 2-methyl-2-butene and a few results on the 174 nm photolysis of propene are also included. At 163 nm (7.6 eV), the main decomposition processes of the photoexcited propene molecule are β(C—H) split (Ф = 0.565) and α(C—C) split (Ф = 0.335). Thus, the β(C—H)/α(C—C) ratio is close to 1.69. In the case of the photolysis of 2-methyl-2-butene, the same ratio is reversed: [Formula: see text] In another work, the ratio obtained in the photolysis of 2-butene was close to unity. Finally, in order to explain the allene and 1,3-butadiene formation in the photolysis of 2-methyl-2-butene, isomerisation of vinylic radical intermediates is proposed, in agreement with observations made by Callear and Lee.
Hydrolysis and ammonolysis of EDTA in aqueous solution
Authors: Motekaitis Ramunas J. , Hayes David , Martell Arthur E. , Frenier Wayne W.
Published: May 2006

The hydrolysis and ammonolysis of EDTA were studied in aqueous solution over a range of temperatures and at various pH values with the aid of nmr, gc, and gc – mass spectroscopic techniques. At high pH in the presence of ammonia, both ammonolysis and hydrolysis occur with the production of N-(2-aminoethyl)iminodiacetic acid (UEDDA), N-(2-hydroxyethyl)-iminodiacetic acid (HEIDA), and iminodiacetic acid (IDA) in molar ratios such that [IDA] = [UEDDA] + [HEIDA]. The first-order rate constant for the disappearance of EDTA at 175 °C in dilute aqueous ammonia is 8.6 × 10−5 s−1 whereas in the absence of ammonia its hydrolysis constant is 4.2 × 10−5 s−1. The value of ΔH0 for this reaction is approximately 35 kcal/mol. When methylamine replaces ammonia, the UEDDA is replaced by N-(2-methylaminoethyl)iminodiacetic acid. The rate of hydrolysis is increased by the presence of a tertiary amine but the latter does not become incorporated into the reaction products. A reaction mechanism is proposed involving bimolecular SN2 attack by base on a carbon atom of the ethylene bridge adjacent to a protonated nitrogen atom of EDTA with concomitant displacement of iminodiacetic acid.
Micellar super-structure in magnetically aligned lyotropic liquid crystals studied by light scattering
Authors: Isolani Paulo C. , Reeves Leonard W. , Vanin J. Atílio
Published: May 2006

Depolarized components of laser light scattering patterns have been investigated for type II lyotropic liquid crystals. These patterns are characterized by intensity maxima and minima with constant angular separation. By using the Bragg equation, a set of distances typical for lamellar arrays can be derived. Two possible models are proposed to explain the results: the first is that the distances are related to the average diameter of lyomesomorphic micelles not accessible to low angle X-ray studies and the second model is a repeating hyperstructure of micellar microdomains.
Differential equation for transport along parallel linear successions of identical symmetrical potential barriers
Authors: Dignam M. J.
Published: May 2006

The differential equation for transport of non-interacting species along parallel paths, each consisting of a linear succession of identical symmetrical potential barriers, is expanded as an infinite series in the derivatives of the electrostatic potential and concentration. The first order expression is shown to represent the model adequately for all but extremely high space charge concentrations and/or extreme departures from steady-state conditions. Under the appropriate limiting conditions it reduces to the well-known linear transport equation, and to the Mott–Cabrera equation, but extends these to higher concentrations since the formulation forbids hops into occupied sites. The treatment leads to a concentration independent diffusion coefficient, but to a concentration dependent mobility.
Carbonyl oxygen exchange of glycol monoesters. Rate and equilibrium constants for the formation of a tetrahedral intermediate
Authors: McClelland R. A. , Ahmad M. , Bohonek J. , Gedge S.
Published: May 2006

Kinetic investigations of the hydrolysis of the 2-phenyl-4,4,5,5-tetramethyl-1,3-dioxolenium ion and 2-phenyl-2-methoxy-4,4,5,5-tetramethyl-1,3-dioxolane furnish rate constants for all three reaction stages of the ortho ester hydrolysis: (1) generation of the dioxolenium ion, (2) hydration of this ion to form hydrogen ortho ester, and (3) breakdown of this species to pinacol monobenzoate. The equilibrium constant for stage (2) can also be obtained. This study complements a previous investigation of 2-phenyl-2-alkoxy-1,3-dioxolanes where similar information was obtained.The rate constants for carbonyl oxygen exchange of the ester products of these reactions, pinacol monobenzoate and ethylene glycol monobenzoate, have been measured. This reaction is shown to proceed by a different mechanism to that normally associated with exchange of carboxylic acid derivatives: cyclization of the glycol monoester to form hydrogen ortho ester, followed by loss of the labelled exocyclic OH group to give 1,3-dioxolenium ion. Reversal of these steps, initiated by an unlabelled water molecule, results in exchange. The relationship of this mechanism with that of the ortho ester hydrolysis is obvious; it is shown that the exchange provides rate constants for the reverse of stage (3). This means that both the forward and reverse rates of this process have been obtained, and this provides the equilibrium constant.
Selective O-demethylation of isoquinoline alkaloids: Preparation of hydrocotarnoline from hydrocotarnine and conversion of S-(+)-laureline into S-(+)-roemerine via S-(+)-mecambroline
Authors: Minamikawa Jun-Ichi , Brossi Arnold
Published: May 2006

The methoxy group in the simple isoquinoline alkaloid hydrocotarnine and in the aporphine alkaloid S-(+)-laureline can be cleaved selectively with trimethylsilyl iodide in boiling o-dichlorobenzene in the presence of DABCO, affording hydrocotarnoline and S-(+)-mecam- broline, respectively. Deoxygenation of S-(+)-mecambroline afforded S-(+)-roemerine.
An abinitio and ion cyclotron resonance study of the protonation of borazine
Authors: Doiron C. E. , Grein F. , McMahon T. B. , Vasudevan K.
Published: May 2006

The gas phase ion–molecule reactions and proton affinity of borazine have been investigated by both theoretical ab initio and ion cyclotron resonance techniques. The experimental proton affinity has been determined from competitive proton transfer equilibria with standard reference bases and found to be 196.4 ± 0.2 kcal/mol. Ion–molecule reaction schemes for reaction of borazine molecular ions have been proposed. Ab initio calculations find the proton affinity of borazine to be 203.4 kcal/mol and the most energetically favorable structure of the borazinium ion is one in which very little structural change occurs relative to neutral borazine with the exception of the geometry about the protonated nitrogen atom. Charge distributions and bond lengths are used to explain bonding changes upon protonation.
Influence de différents catalyseurs à base d'éléments de transition du groupe VIII sur la polymérisation du norbornène
Authors: Taniélian Charles , Kiennemann Alain , Osparpucu Temel
Published: May 2006

Both types of norbornene polymerisation with homogeneous catalysts have been studied. Palladium leads to vinyl-type polymerisation whereas rhodium and ruthenium lead to ring opening. In the case of palladium-catalysed polymerisation we have been able to trap the reactive intermediate PdCl2(C7H10)4 and have studied its behaviour during polymerisation. With ruthenium we have studied the effect of two ligands: cyclopentadiene which leads to a complete blocking of the reaction and triphenylphosphine the effect of which varies according to the ratio [Formula: see text]. Use of the three alcohols, ethanol, n-butanol, and tert-butanol, as solvent shows a variation in reaction rate on charge using RuCl3•3H2O but no change for [Formula: see text]. This indicates that the role of the alcohol is not limited to that of solvent but it must participate in the reaction especially during the formation of the reactive intermediate. [Journal translation]
Regiospecific preparation of 10-allyl-1-ketoquinolizidine and an unexpected disproportionation during its Wolff–Kischner reduction
Authors: McIntosh John M.
Published: May 2006

Regiospecific formation of 10-allyl-1-ketoquinolizidine (7) is achieved in high yield by a [2.3] sigmatropic rearrangement of N-allyl-1-ketoquinolizidinium bromide (6). Wolff–Kischner reduction of 7 affords 10-allylquinolizidine (8) contaminated by the 10-propyl and 10-ethynyl analogs in amounts which depend on the reaction conditions. The carbon-13 spectrum of 8 indicates a trans-fused ring system with an axial substituent at C-10.
Nuclear magnetic resonance reorientational correlation functions: the odd-valued spectral components
Authors: Fouques Catherine Elisabeth Marie , Werbelow Lawrence G.
Published: May 2006

Practical consequences attributable to nonvanishing imaginary spectral components of the second rank spherical harmonic angular correlation function are described in detail. This analysis presumes the absence of macroscopic spatial anisotropies. Modulation frequency, anisotropy, and cross correlation of interaction between a nuclear spin and the extranuclear environment are considered. These findings permit a critical assessment of the second-order ultrafine dynamic frequency shift in the nuclear magnetic resonance experiment.
On the relationships between 18O-transfer, diastereotopic selectivity, and asymmetric induction in an intramolecular Pummerer reaction
Authors: Wolfe Saul , Kazmaier Peter Michael , Auksi Hillar
Published: May 2006

The cyclization of benzyl 2-carboxyphenyl sulfoxide (1) to 2-benzylbenzoxathiane-6-one (2) has been examined by a combination of 18O-labelling of the sulfoxide oxygen, stereoselective deuterium labelling in the benzylic position, and the use of optically active compounds. With dicyclohexylcarbodiimide (DCC) as the cyclizing agent, the reaction proceeds with 55.8% retention of the sulfoxide oxygen, 57.8% preference for abstraction of one of the diastereotopic methylene protons, and it produces a 61.4/38.6 mixture of enantiomers. It is proposed that all three experimental observables are controlled by the competition between initial attack of the DCC upon the sulfoxide oxygen and upon the carboxyl group, and a mechanism is proposed for the reaction which clarifies the relationship between these observables. In agreement with earlier work by Stridsberg and Allenmark, DCC affords 2 having the opposite sign of rotation from 1, and acetic anhydride affords 2 having the same sign of rotation as 1. Asymmetric induction in the latter reaction is significantly less than with DCC because of competing epimerization at sulfur, but the origin of the differences in the sign of rotation of 2 under the different conditions has been clarified by the finding that there is less than 40% retention of the sulfoxide oxygen with acetic anhydride as the reagent.
Conformational analysis of acyclic compounds with oxygen–sulphur interactions. Part VI. Some 1-thioderivatives of 2-propanol and its acetates
Authors: Alcudia Felipe , García Ruano José L. , Rodríguez Jesús , Sánchez Félix
Published: May 2006

A conformational study of 1-X-2-propanol (X = SH, SMe, SOMe, SO2Me, +SMe2) and their O-acetyl derivatives (X = SMe, SOMe, SO2Me, and +SMe2) is reported. From the relative values of the vicinal coupling constants in 1H nmr spectra it has been possible to establish the conformational preference. When a density of opposite charge is supported by heteratoms, polar factors determined a great predominance of that conformation in which the sulphur function has an anti-relationship with respect to the methyl group. In thiol and thioethers the conformational preference is not so marked.
Ipso nitration XXI. Nitration of p-tolylalkanoic acids and derivatives: spiro adducts
Authors: Fischer Alfred , Leonard David R. A. , Röderer Rolf
Published: May 2006

Nitration of 4-(p-tolyl)butyric acid and of 3-(p-tolyl)propionic acid in acetic anhydride gives good yields of the diasteriomeric spiro lactone adducts 1 and 12, respectively. Nitration of methyl 4-(p-tolyl)butyrate, 4-(p-tolyl)butanol, and 4-(p-tolyl)butyl acetate gives nitronium acetate adducts but does not give spiro adducts.
Structural elucidation of the capsular polysaccharide antigen of Neisseria meningitidis serogroup Z using 13C nuclear magnetic resonance
Authors: Jennings Harold J. , Rosell Karl-Gunnar , Kenny C. Paul
Published: May 2006

The capsular polysaccharide antigen from Neisseriameningitidis serogroup Z contains equimolar quantities of 2-acetamido-2-deoxy-D-galactose, glycerol, and phosphate. Carbon-13 nuclear magnetic resonance indicates that the polysaccharide is composed by a repeating unit of 1′-O-2-acetamido-2-deoxy-α-D-galactopyranosyl-glycerol joined through phosphate diester groups at O-3′ of glycerol and O-3 of the galactosamine residue. Assignments of the signals in the carbon-13 nuclear magnetic resonance spectrum were made by consideration of the previously assigned signals of related monomers and oligomers. When applied to a Karplus type relationship the values of the 3J(13C–31P) coupling constants were consistent with the polysaccharide having an extended conformation.
Binuclear palladium complexes of 3,5-disubstituted pyrazoles
Authors: Powell J. , Kuksis A.
Published: May 2006

A series of binuclear palladium 3,5-disubstituted pyrazole complexes of the general formulation [(CH3−nXnCO2)(pzH)Pd(µ-pz)]2 where pz = 3,5-dimethyl or 3,5-diphenylpyrazole, X = F, Cl, Br, C6H5, n = 0–3, were prepared. These complexes are unique in that they contain both bridging pyrazolyl and monodentate pyrazole groups.
Neutral pyrazolyl-bridged nickel nitrosyl complexes. Synthesis, structure, and reactivity
Authors: Chong Kenneth S. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

A series of neutral pyrazolyl-bridged nickel nitrosyl complexes, [LNi(NO)]2 (where L = pyrazolyl, N2C3H3; 3,5-dimethylpyrazolyl, N2C5H7; or 3,5-di-tert-butylpyrazolyl, N2C11H19), is described. The nickel atoms are susceptible to nucleophilic attack and the reactivity of the dimers with neutral donor ligands is reported. In addition to the dimeric molecules a novel trimetallic nickel compound [(ON)Ni(N2C5H7)2]2Ni has also been isolated. Crystals of [Ni(NO)(N2C5H7)]2 are monoclinic, a = 18.925(2), b = 11.012(1), c = 7.037(2) Å, β = 100.93(1)°, Z = 4, space group C2/c and crystals of [(ON)Ni(N2C5H7)2]2Ni are triclinic, a = 7.4041(7), b = 9.6331(7), c = 9.7595(8) Å, α = 85.698(9), β = 73.174(8), γ = 76.109(8)°, Z = 1, space group [Formula: see text]. Both structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to R = 0.035 and 0.028 for 832 and 2128 reflections with I ≥ 3σ(I) respectively. Nearly planar centrosymmetric molecules of [Ni(NO)(N2C5H7)]2 contain trigonal planar nickel atoms with Ni—N(pyrazolyl) = 1.880(3) and 1.922(3), Ni—NO = 1.616(4), and N—O = 1.158(4) Å, Ni—N—O = 178.9(4)°. This structure also contains an unusually long N—N bond in the pyrazolyl ring (1.463(4) Å). Centrosymmetric molecules of [(ON)Ni(N2C5H7)2]2Ni contain a central square-planar Ni(II) atom bonded to four pyrazolyl nitrogen atoms (mean Ni—N = 1.905(1) Å) and two trigonal planar outer nickel atoms coordinated to two pyrazolyl nitrogen atoms (mean Ni—N = 1.922(3) Å) and to a somewhat bent nitrosyl group (Ni—N = 1.625(3), N—O = 1.153(4) Å, Ni—N—O = 168.9(3)°).
Pyrolysis of triethylgallium by the toluene carrier technique
Authors: Paputa Michellene C. , Price Stanley James W.
Published: May 2006

The pyrolysis of triethylgallium has been studied in a toluene carrier gas system in the temperature range of 464.7 to 700.7 K and a pressure range of 0.82 to 3.73 kPa. From the data obtained from this work, the following mechanism for the thermal decomposition of the metal alkyl is proposed:[Formula: see text]where [1] is the rate determining step. After runs below 606 K were corrected for the contribution of a concurrent residual reaction, a least-squares analysis of experimental results from 567 to 651 K based on both product and residual alkyl analysis gave[Formula: see text]at 1.60 kPa.The rate constant, k1, is very slightly pressure-dependent as revealed by tests at 648.0 K (80% and 45% decomposition). Studies indicate there is no detectable surface catalysis effect. Similarly, no effect was observed for changes in concentration or contact time.The mechanism for the formation of polymeric gallium hydride in reaction [4] is not clearly defined and may consist of more than one step. Reaction [5] is slow but based on the C2H4:H2 ratio must occur to a significant extent (40–80%) during a run. Further decomposition occurs between runs, causing a build-up of H2 in the reaction vessel.Experimental data for the hydrogen abstraction by ethyl radicals from toluene[Formula: see text]yield the equation[Formula: see text]
Coefficients B de viscosité dans les systèmes ternaires aqueux. III. Halogénures alcalins–alcool tert-butylique–eau à 25 °C
Authors: Palma Marc , Morel Jean-Pierre
Published: May 2006

We have measured the coefficient of viscosity B at 25 °C of HCl, LiCl, NaCl, KCl, RbCl, KI, and KBr in the mixtures of aqueous organic solvents containing from 10 to 40% tert-butyl alcohol by weight (X), the concentration of electrolyte varying from 0.1 to 0.3 M.Plots of B = f (x) show points of inflexion and minima whose positions can be explained by the structural properties of the mixed solvent.In water, a linear relationship between the entropy of hydration and coefficient B of the ions is observed. In the same way, it can be shown that a linear correlation exists between the entropy of solvation and coefficient B of the electrolytes for all the mixtures studied.These correlations lead to the characterization of two distinct zones (X < 20% and X > 20%) for the range of tert-butyl alcohol–water mixtures. [Journal translation]
Raman spectroscopic studies of structural properties of solid and molten states of the magnesium chloride – alkali metal chloride system
Authors: Brooker M. H. , Huang C.-H.
Published: May 2006

Raman spectra have been recorded for solids and melts of composition MgCl2 + nACl (n = 0–4 and A = Cs, Rb, K, Na, Li). Characteristic spectra have been observed for each of the solids predicted from phase diagram studies and an additional two compounds formulated as Rb3MgCl5 and K3MgCl5 were detected. The compounds Cs2MgCl4, Cs3MgCl5, and Rb3MgCl5 contain the discrete MgCl42− tetrahedral ion which has been characterized by its Raman spectrum. These compounds melt with retention of the MgCl42− ion. Most other solids appear to contain distorted network octahedra with face-, edge-, or corner-shared chlorides. These solids melt to give the more stable tetrahedral MgCl42− ion. In melts of high MgCl2 concentration a new peak was detected which appears to be characteristic of the dimeric Mg2Cl73− ion which exists in equilibrium with the MgCl42− ion. The results are compared to similar studies on the better characterized CsCl–AlCl3 system.
Factor analysis as a complement to infrared band resolution. VII. The temperature dependence of the self association of phenol in carbon tetrachloride solution
Authors: Petelenz B. U. , Shurvell H. F.
Published: May 2006

Infrared absorption bands in the OH stretching region of phenol in carbon tetrachloride solution have been recorded for various concentrations and at several temperatures between 25 and 60 °C. Factor analysis of the digitized spectra was carried out and the presence of three absorbing components in the OH stretching band was indicated at all temperatures in the range of 25–60 °C. The three components are assigned to monomer, linear dimer, and a polymeric species. It is suggested that the polymeric species is a cyclic trimer.Band contour resolution was carried out to obtain areas of the component bands. The variation of the monomer and dimer band areas with temperature was used to obtain a value for the enthalpy of dimerization of −15.8 ± 0.6 kJ mol−1.
Ion–molecule reactions in dimethylsulfoxide by high pressure photoionization mass spectrometry
Authors: Stone John A. , Lin Margaret S.
Published: May 2006

Dimethylsulfoxide (DMSO) has been photoionized at 10.0 and 11.7 eV over the pressure range 0.3–210 mTorr. The rate constant for the disappearance of DMSO+ is 1.0 × 10−9 cm3 molecule−1 s−1, independent of photon energy. The major products at low pressure are CH3SO(CH3SO)CH3+ and CH3SOHCH3+ while at high pressure the ion series (DMSO)nH+ predominates with n ≤ 5. In experiments with mixtures of DMSO and water or methanol very little mixed solvation of the proton was observed although isotopic D/H exchange between D2O and (DMSO)2H+ is facile.
Hydrodesulphurization mechanism of thiophene and tetrahydrothiophene on a cobalt molybdenum catalyst
Authors: Pazos José M. , Andréu Paulino
Published: May 2006

The hydrodesulphurization mechanism of thiophene and tetrahydrothiophene has been developed at high pressures and over a broad range of temperature and contact time on a commercial CoMo—Al2O3 catalyst. The influence of the pretreatment on the catalyst activity and stability was also studied. The pretreatment with a mixture of H2 and H2S was found to be the most convenient. It was found that the sulphur uptake of the fresh catalyst increases with temperature and that an excess of sulphur in the catalyst leads to an initial higher activity.The thiophene reaction seems to occur simultaneously by two pathways: one consists of ring opening, and the second is yielding tetrahydrothiophene. The latter is the slowest step. The tetrahydrothiophene reacts faster than the thiophene and its reaction mechanism involves mainly the rupture of the C—S bond. However, thiophene was detected in small concentrations, showing the contribution of a second route for the tetrahydrothiophene hydrodesulphurization. Experiments carried out with benzene seem to indicate the existence of three different kinds of active sites in the catalyst: desulphurization, aromatics hydrogenation, and olefin saturation sites.On a élaboré le mécanisme d'hydrodésulfurisation du thiophène et du tétrahydrothiophène à haute pression et sur une large échelle de température et de temps de contact avec une catalyseur commercial mixte: CoMo—Al2O3. On a également étudié la stabilité ainsi que l'influence d'un traitement préalable sur l'activité du catalyseur. On a trouvé que le traitement préalable, par un mélange de H2 et de H2S, est celui qui convient le mieux. On a constaté que la fixation de soufre sur le catalyseur frais augmente avec la température et que l'excès de soufre sur le catalyseur conduit à une activité initiale plus forte.
On the chemistry and high field nuclear magnetic resonance spectroscopy of rapamycin
Authors: Findlay John A. , Radics Lajos
Published: May 2006

Base catalysed hydrolysis of rapamycin (C51H79NO13) affords six neutral compounds identified by chemical and spectroscopic means as 2a, 3b, 3d, 5, 2,4-dimethylphenol, and L(−)-piperidine-2-carboxylic acid 6, and whose generation has been plausibly rationalized. These findings as well as detailed analyses of 13C nmr and 1H nmr spectra provide independent corroboration of the X-ray derived rapamycin crystal structure 1. Structurally homogeneous in the solid state, rapamycin is found to occur in solutions as a mixture of two conformational isomers (approximately 4:1). Through nearly complete assignment of the high field 1H (400 MHz) and 13C (100.6 MHz) nmr spectra, the isomerism is shown to be associated with trans–cis rotation of an amidic bond within the 31-membered macrolide ring. The predominant form corresponds to the conformer portrayed by X-ray analysis.
Magnetic and spectroscopic studies on nickel(II) and copper(II) complexes of some neutral tridentate ONS ligands
Authors: Ali M. Akbar
Published: May 2006

New Schiff base ligands formed from 2-methoxybenzaldehyde and 2,4-dimethoxybenzaldehyde with N-methyl-S-alkyldithiocarbazates and their nickel(II) and copper(II) complexes have been prepared and characterised by elemental analysis and magnetic and spectroscopic measurements. The Schiff bases behave as neutral tridentate chelating agents forming stable nickel(II) complexes of stoichiometry NiLX2•xC2H5OH (L = 2-methoxy- or 2,4-dimethoxybenzaldehyde Schiff bases of N-methyl-S-methyldithiocarbazate; X = I−, SCN−; x = 0, 1). Conductivity, magnetic, and spectral data support an octahedral structure for the nickel(II) complexes. The CuLCl2 complexes were also isolated. Magnetic and spectral evidence are in accord with a chloro-bridged dimeric structure. The chloro-complex of copper(II) with the 2-methoxybenzaldehyde Schiff base displays a room-temperature magnetic moment of 1.81 BM, which remains virtually constant over the temperature range 343–123 K.Hydrated copper(II) chloride promotes complete hydrolysis of the 2,4-dimethoxybenzaldehyde and 2-methoxybenzaldehyde Schiff bases of N-methyl-S-benzyldithiocarbazate with the concomitant formation of copper(II) complexes of the parent N-methyl-S-benzyldithiocarbazate of general formula, Cu(N—SR)Cl2 (R = C6H5CH2—).
Synthesis of maytansinoids: the aromatic moiety of maytansine
Authors: Ho Pak-Tsun
Published: May 2006

A simple and novel synthesis of the tetrasubstituted aromatic compound related to the "western–southern" region of maytansine has been achieved.
Solvent effect on the protonation of some alkylamines
Authors: Mucci Alfonso , Domain Robert , Benoit Robert L.
Published: May 2006

Thermodynamic data were obtained at 25 °C for the solution and protonation of six bases B: ammonia, three methylamines, and monoethyl and n-propylamines in dimethylsulfoxide (Me2SO) and propylene carbonate (PC). Vapour pressure, potentiometric, and calorimetric determinations were carried out. The solvent effect on the basicity order and protonation of the amines is analysed by using gas phase data and comparing the solution thermodynamics of gaseous B and BH+. The heat of solution of B in both solvents is close to its heat of condensation. The solution data for BH+ are discussed in terms of two recent hydration data interpretations.
Reactions of bis(ditertiaryphosphine) complexes of rhodium(I) with carbon monoxide, dioxygen, dihydrogen, and hydrogen chloride
Authors: James Brian R. , Mahajan Devinder
Published: May 2006

The products, resulting from addition under mild conditions of the gaseous molecules CO, O2, H2, and HCl, to some rhodium(I)–bis(ditertiaryphosphine) complexes, are described; the [Formula: see text] phosphines used were Ph2P(CH2)nPPh2, n = 1–4, and (+)-diop (diop = 2,3-O-isopropylidene 2,3-dihydroxy-1,4-bis(diphenylphosphino)butane). Monocarbonyls were isolated from addition of CO to [Formula: see text] complexes (n = 1 and 3), the reactions being reversible; there was no reaction with the n = 2 system, while the n = 4 and diop systems absorbed > 1 mol of CO per Rh to give mixtures of products. The same cation precursors add O2 to yield cis-[Formula: see text] adducts (n = 1–3), the binding being reversible for the n = 2 system; pure products were not isolated with the n = 4 cation which absorbs 3 molO2/Rh; the diop system was unreactive toward O2. Reversible additions of 1 mol H2 yield isolable cis-[Formula: see text] complexes with the n = 3 and diop systems; the n = 1 and 2 [Formula: see text] cations are unreactive toward H2, while a mixture of hydrides is formed from the n = 4species. The chlorohydrido cations [Formula: see text] (A = Cl, BF4, PF6, SbF6), n = 1–3, were prepared via routes involving addition of gaseous HCl to precursor [Formula: see text] complexes; however, the reactions with the n = 4 and diop systems did not yield pure products.The solution structures of all the isolated five- and six-coordinate addition products have been determined using 1H and variable temperature 31P nmr. The five-coordinate carbonyl with n = 1 shows equivalent phosphines from −50 to 25 °C, while the n = 3 system shows inequivalent phosphines resulting from a trigonal bipyramidal structure with an equatorial carbonyl. The [Formula: see text] cation, n = 3, has cis geometry, while trans-structures are preferred for the n = 1 and 2 species.
Capture du paradiméthoxyorthoquinodiméthane: synthèses de quinones et d'un intermédiaire de la daunomycinone
Authors: Laduranty Joëlle , Lepage Lucette , Lepage Yves
Published: May 2006

New para-dimethoxyl and para-diacetoxy derivatives in the naphthalene, anthracene, naphthacene, naphtho (2,3-c) thiophene and benzo-c thiophene series are synthesized via the trapping of o-quinodimethanes by various dienophiles. Among these compounds, an intermediate for the synthesis of daunomycinone has been prepared and can be oxidized to a benzoquinone which provides access to new analogues of this important antileukemic agent. [Journal translation]
Synthesis of sugar-organometallic conjugales: ferrocenyl monosaccharide derivatives
Authors: Adam Michael J. , Hall Laurance D.
Published: May 2006

Suitably blocked carbohydrates containing free thio 4, amino 5, and hydroxyl 10, 19 nucleophilic functionalities have been treated with (a) ferrocenecarbonyl chlorides 2 and 3, (b) N,N-dimethylaminomethylferrocene methiodide 12, and (c) ferrocenyl tosylate 16 to form the ferrocenyl sugar derivatives 6, 7, 8, 9, 11, 13, 14, 15, and 20. Direct conjugation of a free, water-soluble sugar to ferrocene was achieved by the formation of a Schiff's base between glucosamine hydrochloride 25 and ferrocene carboxaldehyde 24. The synthesis of ferrocenyl sugars using bridging group technology is exemplified by the conjugation of the thio sugar 4 to ferrocene via the versatile coupling reagent cyanuric chloride 21 to form the s-triazine compound 23. These products have been studied by 1H nmr spectroscopy: chemical shifts, coupling constants, and proton spin–lattice relaxation measurements.
Revision of the structures of partially acylated derivatives of aldose diethyl dithioacetals
Authors: Grindley T. Bruce , Ponnampalam Rathy
Published: May 2006

1H nuclear magnetic resonance spectroscopy is used to correct the structures of most of the known partially acylated derivatives of aldose diethyl dithioacetals which contain more than one acyl group. Previous work had suggested that the hydroxyl group on carbon-2 was the least readily acylated secondary hydroxyl group; current work indicates that it is among the most readily acylated. Evidence is presented which shows that the preferential methylation of aldose diethyl dithioacetals at O-2 is caused by the presence of the sulfur atoms.
Azole derivatives of metals. VI. Binuclear platinum(II) derivatives having both μ-pyrazolato-N,N′ and methoxy or chloride as bridging groups
Authors: Bonati Flavio , Clark Howard C. , Wong Chun S.
Published: May 2006

Binuclear platinum(II) complexes of the type[Formula: see text]where X = H, CH3, Y = H, Br, Z = Cl, OCH3, are synthesized by the reaction of Pt2Cl4(PEt3)2 with the pyrazole and sodium hydroxide in methanol. The nature of the product depends on the amount of sodium hydroxide used.
Thermodynamics of molecular interactions between nitromethane and aromatic hydrocarbons
Authors: Nigam Ram K. , Singh Prem P. , Mishra Ruchi , Singh Mohan
Published: May 2006

Excess volumes of mixing VE, excess enthalpies HE, and excess Gibbs free energies of mixing GE, of binary mixtures of nitromethane with aromatic hydrocarbons have been measured at 303.15 and 313.15 K. The VE, HE, and GE data, which are positive throughout the entire range of concentrations, have been examined with Winnick's theory. The calculated VE, HE, and GE values compare reasonably well with the corresponding experimental values. The theory also correctly predicts the influence of temperature on these excess functions.
Mössbauer study of the reduction of α-Fe2O3 in hydrogen
Authors: Klissurski Dimitar G. , Mitov Ivan G. , Tomov Trifon
Published: May 2006

The kinetics and mechanism of reduction of α-Fe2O3 by hydrogen has been studied by a static circulation method in the temperature range 220–350 °C. It has been established that the reaction order with respect to the hydrogen pressure is 0.86 ± 0.07 and the activation energy of the process is 17.9 ± 0.7 kcal/mol. The kinetic results and the Mössbauer spectra of specimens reduced to different degrees have shown no accumulation of wüstite phase during the reaction.
Influence de la température sur les constantes B.E.T. de dissolution de l'eau dans un mélange fondu [AgNO3 + TlNO3]
Authors: Abraham Marie-Christine , Abraham Maurice , Sangster James
Published: May 2006

The temperature dependence of the B.E.T. constants for water dissolved in the melt (0.515 AgNO3 + 0.485 TlNO3) has been studied in the range 85–110 °C at water mole fractions between 0 and 0.5. The B.E.T. constants are: r: the mole ratio of adsorption sites to salt; ΔE: the difference between the molar energy of adsorption of water on an available site in the melt and the molar energy of liquefaction of water.It was found in this work that (1) r increases linearly with temperature and (2) the product rΔE is perceptibly independent of temperature.
Electrical conductivities of molten zinc chloride – lithium chloride mixtures between 320 and 450 °C
Authors: Benhenda Slimane , Lesourd Jean-Baptiste
Published: May 2006

Specific conductivities of ZnCl2–LiCl liquid mixtures have been determined in the 320–450 °C temperature interval and in the 0–0.54 LiCl mole fraction interval. They were found to increase steadily with both temperature and LiCl mole fraction, which was shown to be related to an increasing ionic character of the melt.
Complexes of substituted benzothiazoles. 2. Copper(II) complexes of the 'tripod' ligand tris(2-benzothiazolylmethyl)amine
Authors: Thompson Laurence K. , Ball Richard G. , Trotter James
Published: May 2006

A series of copper(II) complexes of the title ligand are reported which exhibit both five-coordinate trigonal bipyramidal and pseudo-octahedral stereochemistries. Mixed stereochemistry complexes [Cu(NTBT)X]2[CuX4] (X = Cl, Br), [Cu(NTBT)Br]2[Cu2Br6]•CH3CN, and the complexes [Formula: see text], [Formula: see text], contain trigonal bipyramidal cations while six-coordinate structures are implicated in the Systems [Cu(NTBT)Br2]•H2O and [Cu(NTBT)(H2O)2•MeOH•H2O. The molecular structure of [Formula: see text] has been determined by single crystal X-ray diffractometry. The crystal is monoclinic and belongs to the space group C2/c with Z = 8, a = 24.254(3), b = 14.107(2), c = 16.329(2) Å and β = 105.94(1)°. The complex adopts a distorted trigonal bipyramidal structure (no axial symmetry) with the ligand coordinating in a 'tripod' fashion as an N4 donor. The fifth ligand is a monodentate nitrate. The mean Cu—N distance is 2.07(3) Å and the Cu—O distance is 1.938(3) Å. A second nitrate oxygen atom is close to the copper centre (Cu—O distance 2.783(4) Å) and may represent a weakly bound sixth ligand. Both infrared and electronic spectral data support the presence of a sixth ligand.
The partial molal volume of two nickel chelate complexes
Authors: Sze Y. K. , McBryde W. A. E.
Published: May 2006

Partial molal volumes have been determined for the nickel(II) complexes of ethylenediaminetetraacetic acid (mono complex) and methyliminodiacetic acid (bis complex). The formation of these is accompanied by appreciable increases in volume, greater in the case of the second ligand. The observations are discussed in terms of reduced electrostriction of water by the complexes, and the different volume increases are accounted for by structural features of the complexes which are partially confirmed by spectral measurements.
Potentiometric measurement of H+ concentrations for aluminum orthophosphate titration curves
Authors: Gamble Donald S.
Published: May 2006

A potentiometric titration method of measuring accurate H+ concentrations is demonstrated for aluminum orthophosphate solutions. A calibration procedure has been used which permitted the glass electrode to be used as a concentration probe instead of as a quasi-activity probe. The random error "background noise" has been reduced by the use of Fortran computing for chemical calculations, data handling and sorting, and averaging by least squares poly nomial fits. The distribution of experimental errors along the sample titration curve is indicated by estimates for its various regions.
Trihapto cycloheptatrienyl molybdenum and tungsten dicarbonyl compounds incorporating tridentate chelating dimethyl(1-pyrazolyl)(ethanolamine)gallate ligands
Authors: Chong Kenneth S. , Storr Alan
Published: May 2006

The synthesis and physical properties of a series of cycloheptatrienyl molybdenum and tungsten dicarbonyl compounds incorporating dimethyl(1-pyrazolyl)(ethanolamine)gallate ligands have been investigated. The monomeric, pseudo octahedral, complexes have the organogallate ligand occupying a set of facial positions with the cycloheptatrienyl ring situated opposite to the amino nitrogen atom. Proton nmr studies have shown the η3-C7H7 ligand of the complexes to be fluxional in solution at room temperature. In the low temperature limiting 1H nmr spectra of the complexes in solution, however, it is possible to distinguish ail seven protons of the static η3-C7H7 ring owing to the asymmetric nature of the octahedral molecules.
Evidence for cyclopropoxide intermediates in α-methyl H/D exchange of cyclic ketones under homoenolization conditions
Authors: Patel Vijay , Stothers J. B.
Published: May 2006

Base-catalyzed homoketonization of a series of polycyclic cyclopropanols provides strong evidence for the intermediacy of their anions for H/D exchange at α-methyl carbons in polycyclic ketones under homoenolization conditions.
The adsorption of lower trialkylphosphates at the dodecane – water interface
Authors: Sagert Norman H. , Lee Woon
Published: May 2006

The adsorption of tripropylphosphate, triethylphosphate, and trimethylphosphate at the dodecane–water interface has been studied at temperatures from 293 to 313 K. Standard free energies of adsorption were obtained from the lowering of interfacial tensions in the low (< 10−4) solute mole fraction region. Standard enthalpies and entropies of adsorption were then obtained from the temperature variation of the standard free energies of adsorption.Standard free energies of adsorption from dodecane showed little variation with solute chain length, with the exception of trimethylphosphate. On the other hand, free energies of adsorption from water decreased by 3.45 kJ/mol for each methylene group added, again with the exception of trimethylphosphate. Enthalpies of adsorption increased linearly with increasing solute chain length for adsorption from either phase. For each methylene group added, the enthalpy of adsorption from dodecane increased by 2.9 kJ/mol, while that from water increased by 2.4 kJ/mol.Results for tripropylphosphate adsorption and for triethylphosphate adsorption at higher temperatures could be adequately described by the Schofield–Rideal equation of state, but not by simple two-dimensional solution models. Results for trimethylphosphate adsorption and for triethylphosphate adsorption at lower temperatures could not be fitted adequately by either type of equation of state.