Showing papers in "Bulletin des Sociétés Chimiques Belges in 2010"

Studies on organophosphorus compounds XX. syntheses of thioketones

Abstract: Substituted benzophenones, 2-benzoylthiophene, 3-benzoylpyridine, dicyclopropyl ketone, and camphor are converted into the corresponding thioketones after reaction with the dimer of p-methoxyphenylthionophosphine sulfide, 1. Except for the pyridine derivatives (2- and 4-benzoylpyridines, respectively, gave no thioketones) very high yields are found. Under the same conditions dibenzylketone gave 1,3-diphenylpropene-2-thiol and 1,9-benzanthr-10-one yielded the dimer of 1,9-benzanthr-10-thione. Aromatic thioketones are also obtained by reacting gem-dichlorides with 2-methyl-2-propane-thiol in the presence of catalytic amounts of CF3COOH (or AlCl3). A mechanism is suggested based on kinetic measurements. 13C NMR data of the thiocarbonyls of all thioketones are recorded and a function describing the relation between the chemical shifts of CS and CO is found: δCS1.57 δCO=71.45

Studies on organophosphorus compounds XXI. the dimer of p-methoxyphenylthionophosphine sulfide as thiation reagent. a new route to thiocarboxamides†

Abstract: The thiation properties of the dimer of p-methoxyphenylthionophosphine sulfide, 1, has been investigated by performing reactions with a representative series of aliphatic and aromatic primary, secondary, and tertiary carboxamides in the temperature range 80-100 °C using HMPA as solvent. This new method seems to be superior to all others as in most cases quantitative yields are found. Salicylanilide, when reacted with 1, in HMPA, yields salicylthioanilide and a new type of phosphorus heterocycle, 3, whose structure has been determined by NMR-and X-ray analyses. 13C NMR data are tabulated for a series of thioamide carbons.

The synthesis and properties of 1,4‐diketo‐pyrrolo[3,4‐C]pyrroles

Abstract: Syntheses and mechanistic aspects of formation of 1,4-Diketopyrrolo[3,4-c]pyrroles (DPP) are discussed. The chemical reactivity of this novel class of heterocycles is illustrated by specific electrophilic aromatic and N-substitution reactions, as well as by nucleophilic transformations of the bicyclic lactam carbonyl group. X-ray structural analysis of the diphenyl-DPP molecule reveals significant intermolecular hydrogen bonding and π-π interactions in the solid state.

Metal Clusters in Catalysis III. — Clusters as Models for Chemisorption Processes and Heterogeneous Catalysis

Abstract: An analysis of the intrinsic structural, stereochemical and thermodynamic features of metal surfaces vis a vis those of discrete metal clusters suggests that the clusters are attractive models of metal surfaces for chemisorption and heterogeneous catalysis. Chemical and catalytic properties of the two classes are compared.

Effect of Sulfiding Temperature on Activity and Structures of CO‐MO/AL2O3 Catalysts. ii

Abstract: The 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.

On The State of the Co‐MO‐S Model

Abstract: The present article will discuss the recent developments which have taken place with the “Co-Mo-S model”. Some new results will also be presented to elucidate some of the controversies which have existed in the literature. The Co-Mo-S model, which was originally based on Mossbauer emission spectroscopy (MES) measurements, has now been confirmed and further developed by use of extended x-ray absorption fine structure (EXAFS), infrared spectroscopy (ir), x-ray photoelectron spectroscopy (XPS), high resolution and analytical electron microscopy (HREM and AEM), magnetic susceptibility and other methods. The following are some of the main conclusions: (i) Mo is present mainly as MoS2-like phases; (ii) in the catalytically active Co-Mo-S structures, the promoter atoms are located at the edges of the MoS2-like structures; (iii) the chemical and catalytic properties of the Co edge atoms are strongly influenced by the MoS2 “support”; (iv) in typical alumina supported catalysts, the MoS3 domains appear to be predominantly present as small single sheets which have a large fraction of the Mo atoms present at edge positions (this is an important property since it allows highly active catalysts to be prepared); (v) the presence of Co9S8, cobalt in the alumina or unpromoted MoS2 is seen to have little influence on the HDS activity; (vi) in typical Co-Mo/Al2o3 catalysts strong interactions exist between Co-Mo-S and the support probably in the torn of Mo-S or Mo-O bridges to the alumina (this influences both the chemical and catalytic properties of Co-Mo-S); (vii) the Co-Mo-S model can explain the catalytic behavior of unsupported and supported catalysts including carbon supported catalysts; (viii) besides Co-Mo-S, evidence for similar Ni-Mo-S, Co-M-S, Ni-W-S and Fe-Mo-S structures has been found. The promotional effect depends on the nature of the atoms at the MoS2 (or WS2) edges and for Fe-Mo-S, the effect is slightly negative; (ix) the nature of the active sites has been observed to be different in unpromoted and promoted catalysts; (x) for unpromoted Mo catalysts edge sites have a higher HDS activity than corner sites; (xi) Co-Mo-S and Ni-Mo-S type structures have also been observed to play a role in hydrogenation.

The mineral in bone, dentin and tooth enamel

Abstract: Detailed knowledge about the constitution and the solubility behaviour of the mineral in calcified tissues is still lacking. This knowledge is important for the understanding of the behaviour of the mineral under physiological and pathological conditions. In this study literature data on the composition and particle size of the mineral are reviewed. Their predominantly apatitic nature goes back to hydroxyapatite as their prototype. However, other calcium phosphates, like whitlockite, are also important. The various analytical data on the content of Ca, P, Na, Mg and CO3 as the main components were analyzed for their consistency with a model of variable phase composition of the mineral. This analysis revealed that the probable phase composition of the mineral in dentin and bone is the same, but different from that in tooth enamel. Studies on the solubility behaviour indicate that near the physiological pH (7.4) all phases are solubility controlling simultaneously. This supports a physiological model according to which the body fluids are close to physicochemical equilibrium with bone mineral. Hence, changes in the chemical and phase composition of the mineral which occur under pathological conditions are related to changes in the activities of the relevant components in the surrounding body fluid. The latter depend mainly on cellular activity and organic transport activity. Attention is also paid to the anticariogenic effect of fluoride and the incorporation of that component in the mineral of fluorotic bone. This study is closed with some remarks about the use of synthetic analogues of biominerals as implants in dentistry and surgery.

Mechanismus der Elektrolytischen Wasserstoffabscheidung und Adsorptionsenergie von Atomarem Wasserstoff

Abstract: Les grandes differences dans le cours du degagement electrolytique de l'hydrogene sur les differents metaux doivent provenir principalement de differences dans l'etat de la liaison des atomes H chimisorbes, qui apparaissent comme produit intermediaire dans ces reactions. On en deduit que le ralentissement des reactions en cause est grand dans le cas des liaisons d'adsorption tres faible et tres forte et que pour une liaison de solidite moyenne, les vitesses de reactions passent par un maximum. Ceci rend compte de la position privilegiee des metaux de la famille du platine. Une discussion des mecanismes de reaction possible montre que, en general, un mecanisme de Volmer-Heyrovsky (elimination des atomes H adsorbes par desorption electrochimique) doit etre favorise. Ce n'est que pour les metaux avec des energies d'adsorption dans le voisinage de l'optimum pour ces vitesses de reaction que l'on peut s'attendre a une participation plus ou moins grande de la reaction de Tafel (elimination des atomes H adsorbes par recombinaison).

Studies on organophosphorus compounds XXII The dimer of p-methoxyphenylthionophosphine sulfide as thiation reagent. a new route to O-substituted thioesters and dithioesters†

Abstract: Simple alifatic and aromatic esters, such as ethyl, iso-propyl, and benzyl benzoates, benzyl butanoate, ethyl heptanoate, and ethyl 1- and 2-naphthoate, respectively, react with the dimer of p-methoxyphenylthiono-phosphine sulfide 1 in anhydrous xylene at 140°C to give the corresponding 0-substituted thioesters in nearly quantitative yields. Also simple alifatic and aromatic S-substituted thioesters, such as S-phenyl, S-benzyl and S-tert-butyl thiobenzoates, S-phenyl and S-benzyl thioacetates, and S-ethyl thiobutanoate, produced the corresponding dithioesters in nearly quantitative yields upon treatment with 1 in anhydrous toluene at 110°C. 13C NMR data for the carbonyl- and corresponding thiocarbonyl carbons, have been recorded and a linear relation between the chemical shifts of CS and CO is found: δ(CS) = 1.75·δ (CO) - 79.6 for 0-substituted thioesters and δ(CS) = 1.31.δ (CO) - 22.1 for dithioesters. An anomalous reaction has been observed: Thiobenzoic acid, S,S'-methylene ester 2 reacted with 1 to give 4,5-diphenyl-1-1,3-dithiol-2-thion 3.

Mechanism of the Catalytic Reduction of Hydroperoxides by Ebselen : A Selenium - 77 Nmr Study

Abstract: Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one 1, a non-toxic selenium containing heterocyclic compound has been shown to display both anti- inflammatory activity in vivo and GSH-Px-like activity in vitro. Using 1H and 77Se NMR we investigated the mechanism of reduction of hydroperoxides by thiols in the presence of 1. A catalytic cycle depending on the formation of diselenides and selenenylsulfides was found. The selenenic acid oxidation level present in compound 1 is particularly stable because of the intramolecular cyclisation. This contrasts with previously reported results concerning the oxidation of organoselenium compounds.

Carbon - Supported Transition Metal Sulfides

Abstract: First, second and third row transition metal sulfides ranging from group VI to group VIII c, supported on activated carbo~ were evaluated for their ability to catalyze the hydrodesulfurization of thiophene at atmospheric pressure. x-ray photoelectron spectrosccpy was used to measure the chemical state and to obtain an indication of the dispersion of the supported sulfide particles. Second and third row elements display volcano curves with catalytic activity varying over more than an order of magnitude and maxima occuring at Rh in the second and Ir in the third row. First row elements show a twin-shaped pattern with maximum activity located at Cr and Co. The resemblance of these experimental activity trends with those previously reported for unsupported transition metal sulfides demonstrate the advantage of carbon s uppo rts in studies on the intrinsic catalytic properties of small sulfide particles. A correlation between the catalytic activity of second and third row elements and the shift in XPS binding energies between metal and metal sulfide phases was found. Superior catalysts have low binding energy shifts and preserve a high degree of metal character under sulfiding conditions .

Viscosimètres capillaires modifiés

Abstract: Les auteurs decrivent trois modeles de viscosimetres capillaires particulierement adaptes a la determination des viscosites intrinseques des solutions de hauts polymeres. Le premier type se caracterise par un gradient de vitesse tres faible et une correction d'energie cinetique dite d'Hagenbach insignifiante mcme pour les milieux tres fluides. En plus de ces caracteristiques, les deux autres types presentent les avantages suivants: la dilution de la solution la plus concentree se fait dans le viscosimetre lui-meme ainsi que les filtrations; le trace de la courbe Tisp/c = f (c) ne necessite que 20 a 50 mg de substance et peut etre effectue en moins de deux heures, pesee comprise; enfin la determination des viscosites de polymeres solubles uniquement a chaud, comme le polythene, est considerablement facilitee ainsi d'ailleurs que toute mesure viscosimetrique a haute temperature.

NMR experiments on ketals VI. PMR spectra of alkyl substituted 1, 3‐dioxanes with rigid or anancomeric structures

Abstract: PMR coupling values and shifts of twenty three 1, 3-dioxanes with rigid structure have been determined. The coupling data are in accordance with a chair conformation which is less buckled than that of cyclohexane derivatives. It is necessary to take into account the recently recognized influence of free electron pair orbitals on gem and vicinal coupling phenomena (11). An exceptional situation for the equatorial proton on C5 is found, not only for the couplings of this proton, but also for its shift. An influence caused by the shielding of the oxygen atoms (O1 and O3), their (equatorial) p-orbitals overlapping with the C-H orbital, has been shown to be responsible for coupling value variations.

Large scale preparation of versatile chiral auxiliaries derived from (S)-proline1

Abstract: The synthesis of a variety of enantiomerically pure chiral auxiliaries based on (S)-proline and bearing sterically demanding side chains at the pyrrolidine moiety, such as the secondary amines (S)-3,5 and 7 and the hydrazines (S)-6, is described on a molar scale. As key step, the Grignard or RLi addition to the N-benzylated proline ester (S)-1 is used.

A new hypothesis explaining synergy between two phases in heterogeneous catalysis the case of hydrodesulfurization catalysts

Abstract: We propose a new mechanistic model, explaining the properties of catalysts composed of sulfides of Group VI and sulfides of Group VIII metals. Spill-over hydrogen, emitted by the latter, modulates, or controls, the catalytic centers at the surface of the former sulfide. Slightly reduced centers formed by spill-over hydrogen would be active in hydrogenation, and deeply reduced centers, in hydrodesulfurization. The theory resting on this concept of a remote control agrees qualitatively with all the known catalytic and physico-chemical properties of the catalysts.

σ-Conjugation and σ-Aromaticity

Abstract: Resonance integrals between different hybrid AOs do not vanish, contrary to statements in current texts. Bonds in saturated molecules are therefore not localized. Indeed β(sp3, sp3) is much greater than the CC resonance integral in conjugated hydrocarbons. Paraffins are therefore σ-conjugated analogs of π-conjugated polyenes. Additivity of collective properties applies equally to both, for reasons explained by PMO theory. This is why the localized bond model successfully interprets collective properties. Cyclopropanes should then be isoconjugate with benzene and hence σ-aromatic. Various anomalies concerning the chemistry of small ring compounds can be explained in this way. Delocalization in alkyl anions and radicals, due to σ-conjugation, is discussed.

On the Role of Promoter Atoms in Unsupported Hydrodesulfurization Catalysts: Influence of Preparation Methods

Abstract: Unsupported Co-Mo catalysts were prepared by two different methods:by the co-maceration (CM) method and by a new homogeneous sulfide precipitation (HSP) method. Structural examinations by means of XRD and Mossbauer Emission Spectroscopy (HES) show that the CM catalysts contain several phases with Co9S8 being the dominant cobalt containing phase. On the other hand, the HSP catalysts are shown to contain only one CO phase within an extended range of Co/Mo atomic ratios and this phase is the Co-Mo-S phase. Like in the case of supported catalysts, the Co-Mo-S phase is shown to be the phase responsible for the activity, whereas Co9S8 is shown to have little or no influence on the activity. The differences in activity observed between the HSP and CM catalysts as well as other unsupported catalysts studied in the literature all seem to be related to differences in the preparation procedures resulting in different promotional efficiencies for the formation of Co-Mo-S.

Thermodynamics of Mixed Monolayers

Abstract: From the identity of the chemical potential of each component, including the solvent, in the bulk and the surface phase, the Gibbs equation is deduced. Relations are obtained between surface pressure, adsorptions and molar fractions in the bulk phase. The equations hold both for adsorbed and for spread films. A penetrated film is also considered. The relation between molar fraction and surface pressure was tested for the system Na-laurate and sapoalbin, having very different saturation adsorption values. Agreement between theory and experiment is satisfactory.

Metal clusters in catalysis VIII Reduction of triple bonds

Abstract: Reduction of triple bonds in simple molecules remains a relatively difficult, yet very important, type of transformation. The scientific challenge is a catalytic demonstration of this reaction paradigm with molecules like N2, CO, RCN, RNC, RN2+, and RCCR. Presented in a structural and electronic rationale is a potential solution to the challenge with metal cluster catalysts. Relationships of the rationale to metal surface and metalloenzyme reactions are discussed. Basic structural forms considered in the context of bond order reduction and resultant ease of reduction (hydrogenation) are: .

Isoxazolines‐Key Intermediates For Syntheses of Some Naturally Occuring Amino Compounds

Abstract: [3+2]-Cycloaddition of nitrile oxides with alkenes, modification of isoxazoline intermediates, and subsequent cleavage give rise to a variety of functionalized acyclic structures. Each step may be used to diastereoselectively increase the number of chiral centres. Application of this concept to the synthesis of natural amino polyols, amino sugars and hydroxy amino acids is discussed.

Cinétique de L'action de L'acide Nitreux sur les Amides I. Méthode Générale

Abstract: Nous avons fait l'etude cinetique de l'action de l'acide nitreux sur l'acetamide: a cinq temperatures differentes. Les intervalles des concentrations etudiees etaient de 0,50 a 1,20 M en amide, de 1,80 a 2,50 N en acide chlorhydrique, de 2,50 a 4,00 M en ion chlorure et de 1/100 a 1/200 M en nitrite de sodium. La vitesse de la reaction a ete mesuree en determinant le volume d'azote degage en fonction du temps. L'ordre par rapport aux differents reactifs, a ete determine a 25°C: la reaction obeit a l'equation cinetique simplifiee: L'energie d'activation s'eleve a 13,4 Kcal/mole.

Photosensibilisierte C4 Ringsynthesen und die Haupttypen Photosensibilisierter Reaktionen in Lösung

Abstract: The C4-cyclomerization photosensitized by carbonyl compounds is a type of reaction capable of various generalizations. It opens up the synthesis of cyclobutane- and cyclobutene-derivatives often not otherwise amenable. Among the main types of photosensitization the photosensitized C4-cyclomerization belongs to the biradical relais-mechanisms. In some cases the possibility of a mere physical excitation-transfer from the excited sensitizer to the substrates has been eliminated. Presumably in all cases photosensitized C4-cyclomerization occurs via homogeneous catalysis involving the production of short-lived photoadduct-biradicals composed of excited sensitizer and unsaturated substrate.

Transition-Metal-Catalysed Reactions of Diazoesters. Insertion into C-H Bonds of Paraffins Catalysed by Bulky Rhodium(II) Carboxylates: Enhanced Attack on Primary C-H Bonds†

Abstract: Rhodium(II) carboxylates associated with bulky ligands catalyse the insertion of carbalkoxycarbenes (generated from diszoesters) into C-H bonds of normal and branched alkanes with selectivities differing substantially from those associated with non-bulky carboxylates.

Organometallic Complexes as Models for the Adsorption of Thiophenes on Hydrodesulfurization (HDS) Catalysts

Abstract: In this review are discussed the known modes of thiophene coordination η1(S), η2, η4 and η5) in organometallic complexes. Their structures, bonding and stabilities are related to the adsorption of thiophene on heterogeneous hydrodesulfurization (HDS) catalysts. Modes of benzo[b]thiophene and dibenzothiophene coordination in organometallic complexes are briefly summarized.

Recent Developments of the Chemistry of Thiocarbonyl Ylides

Abstract: The cycloaddition of diazoalkanes to CS double bonds furnishes 1,3,4-thiadiazolines which give rise to thiocarbonyl ylides and N2 in a cycloreversion. Thiocarbonyl ylides are nucleophilic 1,3-dipoles which are interceptible by thiones or electron-deficient alkenes and alkynes as dipolarophiles affording 1,3-dithiolanes, dihydrothiophenes and thiolanes, respectively. In the absence of reaction partners, thiocarbonyl ylides undergo electrocyclization, dimerization, β-H abstraction or Wagner-Meerwein rearrangement.

The influence of spatial orientation of free orbitals in pmr spectroscopy influence of vicinal orbitals on 3J and 2J

Abstract: In accordance with recent literature data, it is proposed that an increment of + 2.3 cps and + 1.8 cps is to be added to the vicinal (3J) and gem (2J) coupling values respectively, each time an α-oxygen (or α-nitrogen) atom has one of its free electron pair p-orbitals parallel with the carbon hydrogen bond of one of the protons involved in the coupling under consideration. An influence on 3J coupling values in three membered rings (epoxides) is however not to be considered. Molecular deformations which disturb the parallelity (i.e. in the rigid half chair form of pentacyclic compounds or in the twist form of hexacyclic compounds) nullify this effect. The Karplus rule and the electronegativity rule have regained a great amount of their reliability with this supplementary effect.

The Dissociation and Titration Constants of Polybasic Acids

Abstract: La variation de la “constante de dissociation» des acides macromoleculaires polybasiques en fonction du degre de neutralisation, de la dilution de l'acide et de la teneur en electrolyte de la solution est expliquee par la presence d'une charge negative sur la macromolecule. Par l'attraction des ions d'hydrogene cette charge diminue la tendance de dissociation. Une forme compacte et une charge elevee de la macromolecule et une faible teneur en electrolyte favorisent cette interaction et par consequence entrainent une diminution de la constante de dissociation. Quand la teneur en electrolytes et la constante de dissociation ont ete determinees, le diametre de la molecule en suspension peut etre calcule. Le diametre de la molecule de la gomme arabique derive de cette maniere est en bon accord avec d'autres determinations de la meme grandeur. En introduisant la statistique d'une grosse molecule en chaine, qui porte des charges, on derive une relation quantitative entre la constante de dissociation, la charge et la teneur en electrolyte. Cette relation est representee dans la figure 1.

Sur les propriétés hydrodynamiques des solutions de grandes molécules en chaîne I. Dimensions et viscosité du polystyrène dans différents solvants

Abstract: Polystyrene fractions over a wide range of molecular weights have been studied by osmotic pressure, viscosity and light scattering in different solvents. The hypothesis of the equivalent hydrodynamic sphere has been verified. The interpretation of the viscosity results as a function of the solvent has been possible in accordance with Flory's theory of real configuration of chain molecules in solution.