Propriétés magnétiques de phosphates et silicophosphates de titane

The magnetic properties of titanium phosphates ATiP₂O₇ (A=Na,K,Rb), A₂Ti₂(PO₄)₃ (A=K,Rb), BaTi₂(PO₄)₃ M g₃Ti₄P₆O₂₄ and titanium silicophosphates ATi₃P₆Si₂O₂₅ (A=K,Cs) have been investigated by magnetic susceptibility and electron spin resonance measurements. All the compounds are paramagnetic and the thermal variation of the susceptibility can be described with a Curie-Weiss law χ_m=χ₀+ C_m/T−θ_p. The values of μ_eff per Ti⁺³ and the spectroscopic data obtained from the 77K E.P.R. spectra are discussed as a function of the structural data.     

Méthode de dosage du nickel métallique en présence de composés oxydés de nickel dans des matières complexes (minerals)

During investigations on the behaviour of metallic nickel in HgCl₂-, KCN- and HCl-containing media, it was noticed in certain cases that nickel metal dissolution was achieved, while a mixture of nickel oxides remained absolutely unaltered.The working conditions were determined, and on the basis of the results obtained two methods have been developed for the determination of metallic nickel in the presence of nickel oxides in complex materials, including ores.These methods are described, in detail and the results of the experiments are given: they show that an accuracy of about 5 % can be obtained.     

Détermination des cinétiques de croissance et de dissolution du perborate de sodium tetrahydrate en lit fluidisé

The authors present the results of an experimental study on the crystallization of tetrahydrate sodium perborate in a fluidized bed. The influences of supersaturation, seed crystal size, temperature and solution velocity on the overall growth rate were examined. The overall dissolution rate determined under comparable hydrodynamical conditions for various seed crystal sizes and temperatures is also reported.The growth rate is not very sensitive to the variations in crystal size, the temperature and the hydrodynamical conditions, but it depends on the supersaturation and the presence of some soluble impurities.The comparison between growth and dissolution rates shows that under actual working conditions the diffusional mass transfer step is not the limiting step of the growth mechanism.     

Séparation chromatographique du plomb contenue dans des solutions concentrées de sulfate de zinc

Spectrographic analysis of lead traces in concentrated zinc sulphate solutions is only possible after elimination of zinc and sulphate ions. Two methods of separation on ion exchangers are proposed : the first method consists in a separation of Pb from Zn on an anion exchanger after elimination of sulphate on a cation exchanger; in the second method, the two steps of the separation are realized on the same cation-exchanger column. Both methods are satisfactory, but the second is faster and simpler.The blank of the method is about 1.5 μg Pb (i.e. 0.15 mg Pb/l) for a separation made with 10 ml of electrolyte. The method is therefore suitable for accurate determinations of Pb contents as low as 1 mg/l of concentrated zinc sulpliate electrolyte.     

Contamination Pétrolière de la Microcouche de Surface du Golfe de Fos-sur-mer (Mer Méditerranéee)

Abstract

In a general study on the petroleum contamination of the Fos-sur-mer Gulf (Mediterranean Sea), the surface microlayer was sampled. We present here the first results reported up to date in this area, based on a sampling carried out with a rotating PVC drum at 3 stations in May 1985.

Very high hydrocarbons concentrations were sometimes observed in the surface film, which appears more heterogeneous than the underlaying water column (0.5-2m). Water samples were filtered through fiberglass filters (0.5-1 μm). Both dissolved and particulate phases were separately extracted and analysed, providing evidence that suspended particles are the major vector for the accumulation and the transport of petroleum pollutants in these neritic waters.

The petroleum origin of “total hydrocarbons” fractions is confirmed by GC and HPLC which reveal characteristic features for n-alkanes and polynuclear aromatic hydrocarbons. HPLC analysis of polar (non-hydrocarbons) fractions could indicate their formation from petroleum components. Furthermore, the comparison with the underlying waters shows that volatilization and biodegradation are the major processes affecting hydrocarbons distribution in these superficial waters.

Biological data (bacteria, chlorophylls, ATP and energetic charge) were simultaneously measured and indicated an important inhibition of phyto- and bacterio- neuston regarding to the planktonic organisms.     

Propriétés catalytiques de la montmorillonite intercalée au titane dans l'oxydation de l'alcool allylique (E)-hex-2-én-1-ol

Catalytic properties of Ti-pillared montmorillonite for the epoxidation of (E)-hex-2-en-1-ol allylic alcohol. The present work is relative to the epoxidation of allylic alcohols by a well-characterised Ti-pillared montmorillonite (Ti-PILC) prepared by intercalating polymeric Ti cations formed by partial hydrolysis of TiCl₄ with HCl. The interlayer distance, the specific surface area and thermal stabilities of the resulting pillared clays depend mainly on the pH of the pillaring solution. For a ratio H⁺/Ti = 0.24, the Ti-PILC shows a basal spacing of 2,6 nm and a specific surface area of 316 m²·g^–1, stable up to 773 K. In the conversion of isopropanol, this Ti-PILC shows a Lewis type acidity and a low redox activity. It catalyses the oxidation of allylic alcohol (E)-hex-2-en-1-ol with tert-butyl hydroperoxide in the presence of diethyl tartrate. The yield and nature of the final products depend on the reaction temperature and catalyst activation: no epoxidation could be obtained with non calcined samples. With a solid calcined in air at 773 K and then converted to a Ti-PILC, the main product is hexenoic acid for a reaction below 273 K, while the epoxide of the allylic alcohol is formed with 50 % yield at 298 K. This yield is comparable to that reported for the same substrate for polymer supported Ti(IV) catalysts.     

Conductimétrie des complexes cyanés du mercure (ii) application aux dosages

The formation of complex cyanides of mercury (II) has been studied by conductimetry. The shape of the conductimetric curves at different dilutions and different pH levels may be explained by the initial presence of HgOH⁺ ions and of colloidal hydroxide Hg(OH)₂ then by the successive formation of Hg(CN)₂, HCN and Hg(CN)₄^-2.These hypotheses have been verified by measurements of pH and of oxidation-reduction potential.The dissociation constants of the complexes Hg(CN)₂ and Hg(CN)₄^-2 have been calculated and are 10^-21.7 and 10^-27.7 respectively.A simple conductimetric method has been evolved which allows simultaneous determination of the amounts of mercury (II) and the free acid in a solution. The piesence of Cl^-ions is recommended to increase the precision of the determination.     

Etude du phénomène de dépiégeage des ondes de densité de charge dans les systèmes de basse dimensionnalité

Numerical results of the behaviour of a low dimensional system show that the electric resistivity depends on the friction coefficient generated by the defects. We also show that the electric field dependence of the response time at different friction coefficients follows a power law. The divergence of the charge density wave response time near the threshold field indicates that depinning may be viewed as a dynamical critical phenomenon.     

Cétonisation catalytique du méthyl-2-butène-3-ol-2 par des complexes du rhodium(III) ou du palladium(II)

A number of efficient catalytic procedures for the oxidation of acid-sensitive substrate such as 2-methyl-3-buten-2-ol to the corresponding ketone (2-methylbutan-2-ol-3-one) are compared. Reaction with dioxygen (or quinone) and a palladium precursor (PdCl₂ or [PdCl(NO₂)(CH₃CN)₂]) under mild conditions (⋍ 35°C), gave good conversions (⋍ 98%) and good selectivities (⋍ 90%).     

Chromatographie sur papier des Molybdates. Titrage direct des taches de Molybdène chromatographié, séparé du Chrome et du Vanadium

Résumé Dans les conditions opératoires précisées ici, le molybdène chromatographié sur papier Whatman n°4, se laisse doser parabsorptiométrie à ± 1% près, pour une quantité de l'ordre de 10 microgrammes.Letitrage direct de la même quantité de molybdène se fait à ± 3,5% près. Séparé du chrome et du vanadium par chromatographie, la précision du titrage après chromatographie reste du même ordre. La titration directe fait gagner trois heures sur l'absorptiométrie.

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Summary Under the conditions outlined here, molybdenum chromatographed on Whatman paper No. 4, may be determined by absorption, within about ± 1%, for an amount of the order of 10 micrograms. The direct determination of this same quantity of molybdenum by titration can be made within about ± 3%. Separated from chromium and vanadium by chromatography, the precision of the titration after chromatography remains of the same order. The direct titration gains three hours over absorption.

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Zusammenfassung Bei Einhaltung der beschriebenen Versuchsbedingungen läßt sich Molybdän nach chromatographischer Adsorption auf Whatman-Papier Nr. 4 in der Größenordnung von etwa 10 mit ± 1% Genauigkeit durch Absorptiometrie bestimmen. Die direkte Titration gleicher Molybdänmengen läßt sich mit einer Genauigkeit von ± 3,5% ausführen. Nach chromatographischer Trennung von Chrom und Vanadium ergibt die Titration die gleiche Genauigkeit. Somit lassen sich durch direkte Titration gegenüber der Absorptionsmessung drei Stunden Zeit gewinnen.

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Cette recherche a bénéficié d'un subside du Fonds National de la Recherche Scientifique. Nous en témoignons ici notre sincère gratitude.

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Avec 3 figures.

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Travail exécuté en vue de l'obtention du grade de Licencié en Sciences Chimiques (Faculté des Sciences, Université Libre de Bruxelles), juillet 1952.     

Application de la méthode de Melnikov pour l'étude du roulis non linéaire des navires dans la houle

For studying ship rolling within a global analysis more and more mathematical tools from chaos theory are available. For this purpose, however, drastic simplifications must be applied: (i) rolling is the single degree of freedom, (ii) motion is represented by an ordinary differential equation, and (iii) the study is achieved in the vicinity of vanishing stability. Here the Melnikov method is used in this application. The focus is on ships whose restoring moment is represented with an odd polynomial. Above the fifth degree, a harmonically excited system exhibits frequencies which cancel the fluctuating part of the Melnikov function. Hence the heteroclinic orbits still exist whatever the ‘smallness’ of the perturbation as soon as the system is undamped. The existence of such cancellation is otherwise confirmed from an analysis of the erosion of the attraction basin.     

Etude par RMN de composés organiques contenant des chalcogènes—IX.* RMN du 13C dans des dérivés aromatiques du tellurényle

In order to synthesize new tellurium heterocycles, we prepared o-halogenotellurobenzoyl chlorides. We present and discuss here the results of a ¹³C NMR study of these compounds, together with other intermediates that we have isolated during our synthesis and two new tellurium heterocycles.     

Activité antiplasmodiale in vitro des composés isolés des écorces du tronc de Vitex thyrsiflora

Phytochemical study of Vitex thyrsiflora (Verbenaceae), a medicinal plant commonly used in traditional medicine to treat malaria, have allowed to isolate six compounds identified 20(R),24(E)-3-Oxo-9β-lanosta-7,24-dien-26-oic acid (1), α-amyrin (2), β-amyrin (3), friedelin (4), β-sitosterol palmitate (5) and a sterol glucoside (6). All these compounds were isolated for the first time in this plant. Their structures were determined on the basis of their physical and spectroscopic data (IR, MS, UV, NMR) and by comparison of these data with those reported in the literature. Compound 5 showed significant antiplasmodial activity with IC₅₀ of 3,09 and 8,98 μg/mL against multi-resistant strains Dd2 and K1 of P. falciparum. All these constituents were isolated from this plant for the first time. The tested compounds were non-cytotoxic on the LLC-MK2 monkey kidney epithelial cells. The results obtained can justify the use of Vitex thyrsiflora stem bark in traditional medicine for the treatment of malaria.     

Oxydation catalytique de l'octéne-1 en présence de complexes de rhodium(III) ou de palladium(II) associés à des acides phosphomolybdovanadiques et au dioxygéne

Chlororhodium(III) complexes with heteropolyacids HPAH_3+n [PMo_12−nV_nO₄₀]) catalyze the oxidation by molecular oxygen of oct-1-ene to octan-2-one in alcoholic solvents with alcohol cooxidation (T 60° C).The PdSO₄HPA/water-THF/O₂ catalyst system shows the highest activity at room temperature for this ketonization.     

Champ de force de valence du 3-Méthyl 4-nitro pyridine N-oxyde (POM)

The Simplified Generalized Valence Force Field of the 3-methyl 4-nitro pyridine N-oxide molecule (POM) has been determined. In order to verify the transferability of the force field from the parent molecule 4-nitro pyridine N-oxide (NPO) to POM, the calculations have been made first using the CH distances determined by X-ray diffraction for NPO, and the final results correspond to the real geometry determined by neutron diffraction. Moreover, it has been necessary to re-assign 5 of the observed vibrational frequencies of POM.     

Modélisation des temps de réponse des capteurs chimiques

Modelling consists of considering the response and recovery times of a sensor to the target chemical species, as the sum of an ‘intrinsic’ response/recovery time, independent of the experimental conditions, and of an ‘extrinsic’ one, linked to the volume of the measurement cell and to the fluid flow. The experimental response/recovery times being almost always dominated by the extrinsic part, a dissymmetry between the response and recovery signals is observed for sensors whose response is not linear with the concentration of the target chemical species.     

Fonctionnalisation du polychlorure de vinyle: Greffage de fonctions plastifiantes (type ester d'éthyle-hexyle)

The grafting of plasticizing groups such as 2-ethyl-hexyl ester on PVC has been carried out either in solution or in the gel state through nucleophilic substitution of chlorine atoms, with the help of sodium salts of 2-ethyl-hexyl esters of o-mercaptobenzoic acid and thioglycollic acid. As with sodium thiophenate, the substitution of chlorine atoms is stereoselective with respect to iso and heterotactic triads. The glass transition temperature is lowered as the substitution rate increases and the plasticizing power of grafted 2-ethyl-hexyl ester groups of thioglycollic acid is greater than those introduced by o-mercaptobenzoic acid. Further the plasticizing power of 2-ethyl-hexyl ester groups is decreased when they are grafted on the polymer.