La détermination du vanadium par la méthode spectrophotométrique en solution non-aqueuse

On mixing small quantities of an aqueous solution of vanadium, containing hydrogen peroxide and acidified with HCl, with anhydrous dioxan containing gaseous hydrogen chloride in molar concentration, an intense red-yellow colour appears, in the presence of as little as 5 μg/ml vanadium.If a drop of salicylic aldehyde is added to the solution thus obtained, the colour changes to violet-blue, which shows an absorption maximum at 565 mμ, clearly visible even with 1 μg/ml vanadium.This reaction, though a sensitive method for the detection of vanadium, is not suitable for quantitative measurement of this substance because the small quantity of water introduced in the form of the vanadium solution hydrolyses the coloured compounds.Very good results can be obtained by dissolving the dry residue (at 100°C) of the solution under examination in 0.2 ml of N HCl in 2% aqueous H₂O₂ solution, and then in 5 ml of a solution made up of 40% acetic anhydride containing gaseous HCl (1 N), 40% glacial acetic acid, and 20% methyl Salicylate.By this method as little as 1 μg of vanadium can be determined.Co, Mo, and W, interfere; the other elements do not.     

Stéréochimie des échanges hydrogène-deuterium des protons benzyliques des arènetricarbonylchrome. Echange des protons en syn du métal

Tetralintricarbonylchromium exchanges anti and syn benzylic protons in a solution of potassium tert-butoxide DMSO-d₆. Under the same conditions the syn benzylic tertiary proton of trans-1-methyltetralintricarbonylchromium remains unchanged. The anti and syn benzylic protons of dihydroanthracenetricarbonylchromium and xanthenetricarbonylchromium undergo exchange and trans-9-methyl xanthenetricarbonylchromium undergoes exchange and epiinerisation.     

De l'analyse de la résistance interne par perçage à la détermination du profil de dureté des aciers traités en surface

The thrust measured during a drilling test is related to the hardness of the material tested. When the test is performed on a superficially heat-treated specimen, the results do not exactly correspond to the hardness profile obtained by the Vickers micro hardness technique. The difference is due to the integration of heterogeneous resistance along the cutting edge of the conic drill. By discretising the drilled thickness, we have developed an algorithm yielding the hardness of each elemental thickness. Results are very close to those obtained by Vickers hardness profile measurements.     

La polysilylation directe: une voie rapide d'accès à des modèles d'encombrement stérique très élevé

Reductive tetrasilylation of t-butyl-, trimethylsilyl- and o-bis(trimethylsilyl)benzenes with Me₃SiCl/Li/THF was carried out in high yields, giving the corresponding cyclohexene derivatives [one (1), two (2a and 2b) and one (3) isomers, respectively]. X-Ray structure analysis of 1 and comparison of NMR (¹H, ²⁹Si) data of the four products allowed complete structure assignments. The presence of a t-Bu or Me₃Si group in the vinylic position requires that the Me₃Si group attached to the vicinal Csp³ atom be in the pseudo-axial position. For the first 1,2,3,4,5,6-hexasilylated cyclohexene 3 we propose a pseudo-chair structure in which the four silyl groups attached to Csp³ atoms are in pseudo-axial positions.     

Un nouveau système de coordonnées pour les équations de Darcy-Muskat diphasiques en milieux poreux hétérogènes isotropes à deux dimensions

We address the formulation of two-phase flows in the context of a Darcy-Muskat (DM) model in terms of a saturation/global stream-function (or global pressure) coupling in heterogeneous isotropic porous media. In two dimensions the coordinate system, associated with some infinite capillary limit global stream function-global pressure, allows the saturation evolution to be unidimensional. We show that the complete (DM) model projected on this coordinate system can be very efficiently solved numerically.     

Dosage du chrome,du vanadium et du molybdène par la méthode des indicateurs radioactifs

A radiochemical method for the determination of Cr, Mo, and V by means of radioactive silver is described. Using a solution of radioactive silver nitrate, a standard curve is obtained indicating the activity of the precipitate as a function of the quantity of the metal present. Unknown concentrations of Cr, Mo, or V can be easily determined if the same experimental and geometrical conditions are reproduced.     

Méthode de détermination des épaisseurs de films conducteurs par mesures de résistance de surface

To evaluate the thickness of the layers of a Ti/TiAl₃/Al system, experiments based on surface resistance measurements have been performed. The thickness of each layer is deduced from a comparison among calculated and measured values of resistance. We present here a solution for the simulation of surface resistance and the results obtained with this method on Ti/TiAl₃/Al systems.     

Réactivité des macromonomères styréniques du polyoxyéthylène en transfert radicalaire

During the homo- and copolymerization with butyl acrylate of styrenic macromers of polyoxyethylene, the molecular weight of the polymer is found to increase continuously because of transfer to the polymer. The polymerization of butyl acrylate in the presence of non-polymerizable model compounds of the macromers has been studied. It is shown that the transfer involves chiefly the benzylic protons; the transfer constant is 2.1 × 10^–3, i.e. larger than that corresponding to the ethylene oxide moiety, which is about 3 × 10⁻⁴. A kinetic study shows that the efficiency of the transfer radicals for reinitiation is about 0.75.     

Etude par spectrographie d'absorption infrarouge des produits de décomposition du mélange chlorate de potassium-bioxyde de manganèse

Résumé Le chlorate de potassium, chauffé avec du bioxyde de manganèse, donne de l'oxygène et du chlorure de potassium, sans formation transitoire de perchlorate et de permanganate de potassium.

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Summary Potassium chlorate when heated with manganese dioxide yields oxygen and potassium chloride without transitory formation of potassium perchlorate and permanganate.

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Zusammenfassung Kaliumchlorat zerfällt beim Erhitzen mit Mangandioxyd in Sauerstoff und Kaliumchlorid, ohne daß Perchlorat und Permanganat als Zwischenprodukte gebildet werden.

     

Formulation du contact avec adhérence en élasticité non linéaire entre deux solides déformables

Within the framework of finite deformations and using an approach to the kinematics of contact due to A. Curnier, Q.C. He and J.J. Téléga, we propose a spatial thermodynamic formulation for the problem coupling unilateral condition, friction and adhesion. The adhesion is characterized by its intensity introduced by M. Frémond. In the case of frictionless contact between an hyperelastic body and a plane rigid support, with a particular `static' law for the evolution of the intensity of adhesion, the problem can be reduced to a minimization one for which we can show the existence of a solution.     

Comportement électrochimique du ferrocène,du pérylène et du tétracène dans une électrode à pâte de carbone à liant électrolytique dans les mélanges eau–acide phosphorique

The carbon dough electrode with incorporated electrolyte has been used to analyse the electrochemical behaviour of ferrocene, tetracene and perylene in phosphoric acid media 0.1 to 14.8 M. The cyclic voltammetry results obtained for ferrocene with the carbon dough electrode corroborate with polarographic data. Voltamperometric study of the aromatic hydrocarbon oxidation Ar such that of perylene and tetracene on the carbon dough electrode has allowed to establish the normal potential of the corresponding oxido-reducing systems. The existence of the four oxidation states: Ar, Ar⁺, ArH⁺ and Ar²⁺ at different concentrations of phosphoric acid is specified. The results of this study can be used to establish correlations between some of concentrated solution properties of different acids.     

Spectres d'absorption détectés par effet photoacoustique en infrarouge par transformée de Fourier—applications à quelques médicaments

Photoacoustic detection in Fourier transform i.r. spectrometry has led to spectra obtained without sample preparation. This fact may be a very important advantage in biological applications, but these spectra are not directly in good agreement with transmission spectra. In the present work a simple mathematical correction treatment is presented which is in accord with the theory of the photoacoustic effect. This correction routine is applied to some drugs in view of a possible application to direct identification in pharmaceutical preparations.     

Microstructure et détermination des ramifications alkyle dans une série de copolymères éthylène acétate de vinyle

Compounds suitable as models for copolymers of ethylene with vinyl acetate have been prepared and studied by ¹³C-NMR (62.89 MHz). By mixing model compounds, various branched copolymers were simulated. The results have permitted an assignment more complete than previously reported for these copolymers. An investigation was made on the number of branches in nine separate copolymers. The number of ethyl, butyl, pentyl and longer branches per 1000 carbons in the main chain were determined. The number of ethyl branches was around four branches per 1000 carbons; the number of branches longer than butyl decreased from about 20 to 8 per 1000 carbons with increase in vinyl acetate content; the butyl branches predominated over those of other types when the vinyl acetate content was ⩽25% by weight.     

Contribution à l'étude cinétique du greffage du polyéthylène,en suspension dans l'eau,par l'acide acrylique

The radical grafting, in water suspension, of a polar monomer (acrylic acid) onto a non-polar polymer (low density polyethylene) was studied in the presence of t-butyl peroctoate. A preliminary study of the homopolymerization of acrylic acid was carried out under the experimental conditions used for the grafting and with: [A]₀ = 0.0025 and 0.0050 mol 1⁻¹ and [M]₀ = 0.125, 0.75 and 1.25 mol 1⁻¹. It is shown that the initial rate of polymerization is second order in monomer. The grafting experiments were carried out with [A]₀ = 0.0025 and [M]₀ 0.125, 0.75 and 1.25 mol 1⁻¹. For each experiment, the contents of grafted, homopolymerized and non-polymerized acrylic acid were determined separately. The initial rates of grafting and homopolymerization were determined as well as the orders in monomer. Several preliminary treatments of polyethylene led to a significant increase of the grafting efficiency.     

Evaluation des interactions électroniques en série hétérocyclique par la mesure des aires intégrées des bandes infrarouges: Cas de dérivés du benzothiazole substitués en position 2

Infrared νCN vibration bands of some 2-X substituted benzothiazoles (X=H, CH₃, Cl, F, OCH₃, N(C₂H₅)₂, SCH₃ and CN) have been used through their integrated areas, to establish a correlation with substituent characteristic parameters.     

Nouvelle méthode de synthèse d’acides et d’esters arylboroniques par électroréduction de dérivés aromatiques halogénés en présence d’agents boratants

Novel synthesis of arylboronic acids and esters by electroreduction of aromatic halides in the presence of borating agents. A novel strategy for the one-step synthesis of arylboronic acids and esters by an electrochemical coupling reaction is described. It is based on the reductive coupling between the aromatic halides and a borating agent (trialkyl borate or pinacolborane). The reactions are carried out in DMF or THF with the use of sacrificial magnesium or aluminium anodes in a single-compartment cell. Arylboronic acids and esters are obtained with moderate-to-good isolated yields. To cite this article: C. Laza, E. Duñach, C. R. Chimie 6 (2003).