Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—III. Membranes non-ionisables contenant de la poly-n-vinylpyrrolidone

Equilibrium properties (swelling) and transport phenomena (dialysis) of non-ionizable membranes, obtained by radiation grafting of N-vinylpyrrolidone onto thin PTFE films, were studied. Grafting was conducted by the direct method with monomer solutions in benzene. The overall activation energy of grafting determined between 20 and 50° is high (12.5 kcal mol^?1): the reaction is controlled by the monomer diffusion into PTFE film. The length of grafted chains increases with temperature.The molality of the membranes decreases when the temperature of grafting increases; for a given grafting ratio, the swelling is higher for membranes containing a small number of long grafts than for membranes with numerous short branches. The transfer of both ions and water is a function of the free volume in the films, it depends on the grafting ratio and is not influenced by the preparation conditions.     

Influnce des interactions de torsion dans la reduction des cetones par les hydrures interpretation generale du deroulement sterique de la reduction des cetones acycliques et de l'addition des organomagnesiens sur les aldehydes acycliques

Reduction of ketones L-CHMe-CO-R [L=Ph and Cy(Cy = cyclohexyl) and R=Me, Et, iPr and tBu] affords pairs of diastereoisomeric alcohols L-CHMe-CHOH-R. The predominant diastereoisomer is always that predicted by Cram's rule, and the stereoselectivity of the reaction generally increases as R is made more bulky. Thus, with LiAlH₄ in ether at 35°, the diastereoisomer ratios are respectively 2.8:1, 3.2:1, 5.0:1, and 49:1 when L=Ph and 1.6:1, 2.0:1, 4.1:1, and 1.6:1 when L=Cy. With NaBH₄ in isopropanol at 50°, these ratios are respectively 1.6:1, 2.0:1, 2.7:1, and 7.3:1 when L=Ph, and 1.2:1, 1.6:1, 3.2:1, and 3.5:1 when L=Cy. It is suggested that an important factor determining the steric course of the reduction of both open-chain ketones and cyclohexanones is torsional strain in the transition state, and that torsional strain involving partial bonds can represent a substantial fraction of the strain between fully-formed bonds, even when the degree of bonding is quite low. This postulate has been made the basis of an internally consistent interpretation of the steric course of the reaction between carbonyl compounds and nucleophilic reagents such as hydrides and Grignard reagents.     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—II. Membranes bifonctionnelles

Bifunctional membranes containing both carboxylic and pyridine groups are obtained by successive grafting of acrylic acid and 4-vinylpyridine onto thin films of PTFE. Homogeneous membranes with a random distribution of grafting chains have been prepared by the direct radiation method. Mosaic membranes containing geometrically well defined acid and basic zones are made by pre-irradiation with X-rays using two absorbing shields; the two monomers are grafted in successive steps. The equilibrium and transport properties of these membranes have been determined. They can either result from the addition of the properties of each component (in the case of conductivity) or give rise to a new properties (e.g. abnormal negative osmosis). Whatever the structure of the bifunctional membrane (homogeneous or mosaic), this negative osmosis occurs within a pH range in which the membrane potential varies greatly i.e. when the ionic character of the membrane changes. Experimental data are discussed on the basis of thermodynamics of irreversible phenomena. The phenomenological coefficients characteristic for a membrane belonging to each of the two types (mono- and bi-functional) have been calculated. The reflection coefficient σ is negative: this suggests a potential application of these membranes in piezodialysis.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine: Tome IV. L'extraction des cations trivalents par les oxydes de tri-n-butylphoshine et de tri-n-octylphosphine

The extraction of trivalent lanthanides and actinides by trialkylphosphine oxides is based on the equilibrium Me_a³⁺3+NO_3a^-+3 Alk₃PO₀ ⇌ Me(NO₃)₃·3 Alk₃PO₀ At constant ionic strength (sodium nitrate 2 M), the equilibrium constants for the complex formed between tri-n-octylphosphine oxide in n-octane and ²⁴¹Am or ²⁴⁴Cm have been calculated; the values are respectively(2.9±0.5)·10⁷M^-3 and (1.7±0.15)·l0⁷M^-3.The distribution of lanthanides and actinides between, 0.1 M tri-n-butylphosphine oxide in benzene and nitric acid solutions of different concentrations was examined and discussed.     

Sels de Pyrylium. XVIII. Etude par RMN du Carbone-13 de Sels d'Aminopyrylium et des Barrières de Rotation dans quelques Cations N,N-Diméthylaminopyrylium

The C-2—N bond of 2-N,N-dimethylaminopyrylium cations has a partial π character due to the conjugation of the nitrogen lone-pair with the ring. The values of ΔG^≠, ΔH^≠, ΔS^≠ parameters related to the corresponding hindered rotation have been determined by ¹³C NMR total bandshape analysis. This conjugation decreases the electrophilic character of carbon C-4 so that the displacement of the alkoxy group is no longer possible. Such a hindered rotation also exists in 4-N,N-dimethylaminopyrylium cations and the corresponding ΔG^≠ parameters have been evaluated. Comparison of these two cationic species shows that hindered rotation around the C—N bond is larger in position 4 than in position 2. Furthermore, the barrier to internal rotation around the C-2? N bond decreases with increasing electron donating power of the substituent at position 4. ΔG^≠ values decreases from 19.1 kcal mol^?1 (79.9 kJ mol^?1) to 12.6 kcal mol^?1 (52.7 kJ mol^?1) according to the following sequence for the R-4 substituents: -C₆H₅, -CH₃, -OCH₃, -N(CH₃)₂.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. II. Influence de la variation de la sensibilite du calorimetre avec la temperature sur les valeurs trouvees pour les constantes de vitesse et les enthalpies de reaction

The variation with temperature of the sensitivity of a “Thermanalyse” microcalorimeter has been determined using the electrical calibration system of the apparatus. From the results, a method for the correction of the differential scanning microcalorimetric diagrams has been developed. The influence on the determination of the rate constants during kinetic studies of the decompositions of free radical initiators and on enthalpy measurements has been studied.     

Polymerisation anionique du methacrylate de methyle par les organoalcalins—II. Polymerisation en milieu solvant protonique et influence de la temperature sur les tacticites des polymeres

Anionic polymerization of methylmethacrylate, initiated by fluorenyl-alkali metals in amine media, gives syndiotactic polymers.With amines having high dielectric constant (NH₃ and MeA) Li⁺, Na⁺ and K⁺ give approximately the same values of differential enthalpies and entropies of activation for iso- and syndiotactic placements.With primary amines having moderate dielectric constant (5 < ? < 7), influence of the nature of the counter-ion has been observed. The syndiotacticity increases with increasing alkali cation radius.For the same ion pair, the syndiotacticity of the propagation depends on the nature of the primary amine. From the absorption peak shifts detected by u.v. spectroscopy, it has been suggested that the living carbanion is solvated by amines. Because of this solvation, the coordination bond between the carboxy group of the living chain-end and the counter-ion is weakened; the syndiotactic placement is thus favoured.The strength of the solvation phenomenon depends on the steric hindrance of the amine molecule. Differences between the stereoconfiguration propagations have been observed for the bulky cyclohexylamine and the smaller and less rigid n-butylamine and ethylamine. With iso-propylamine, the behaviour of the anionic propagation is intermediate.Finally, with free ions or loose ion pairs, the anionic propagation is not affected by solvation of the living carbanion.     

Sels d'atdp—20 : Relations reactivite-structure dans les cinetiques de decomposition de sels d'atdp substitues. hypersensibilite a des substituants en position 3 de la

The kinetics of decomposition of various propyloxy phosphonium chlorides, the chain of which is substituted with non polar groups in position 2 and polar groups in position 3, have been measured in pyridine and in DMF. The validity of Taft correlation with σ^* parameters have been ascertained within each of the three linear, branched and neopentylic series, using Exner's criterion. In both solvents, it appeared that the sensitivity parameter ?^* for the neopentylic series varies considerably with the temperature and may reach unusually high values. This phenomenon is interpreted by a proximity effect between the substituent and the seat of the reaction, due to steric constraints.     

Application de la RPE à la localisation des substitutions isomorphiques dans les micas: Localisation du Fe3+ dans les muscovites et les phlogopites

Electron spin resonance spectra attributed to four Fe³⁺ centers designated O_a, O_b, T_a, T_b have been observed in crystals of muscovite and phlogopite. The results are discussed using the spin Hamiltonian

with g_e ～ 2.002. The angular variation of the resonance lines is used to determine the ESR axes of the four different sites. Two species are octahedrally coordinated (O_a and O_b) and are assigned to two different surroundings of Fe³⁺ in the octahedral sheet. The remaining two species (T_a and T_b) may be assigned to the tetrahedral FeO₄. The T_a sites have a symmetry axis lying along one of the FeO bonds. The symmetry axis is created by an excess of negative charge on the oxygen bound to the neighboring tetrahedral substitution. Rhombic symmetry of the T_b sites is due to the presence of fluorine anions substituting some hydroxyl ions. One of the ESR axes is directed toward the fluorine ion.     

Polymerisation en phase homogene du methyl-2 thiiranne amorcee par les thiolates de cadmium et de zinc. Influence des interactions monomere-metal sur la stereoregularite des polymeres

The stereoregularity of polymethylthiiranes initiated by zinc and cadmium thiolates depends upon the nature of the metal, temperature, solvent and the monomer/initiator concentrations ratio. Complexation of the metal with monomer has been studied by (¹³C) and (¹H) NMR on a model molecule, dimethylcadmium. Cryoscopic measurements made on a soluble cadmium thiolate have shown the presence of aggregates. The relationship between these observations and polymer stereoregularity is discussed.     

Sels d'alkyloxyphosphonium—XV: Activation de l'hydroxyle anomere des 2,3,4,6-tetra-o-acyl-d-glucopyranoses—II. Preparation d'orthoesters et de thioglucosides

The joint action of tris(dimethylamino)phosphine (TDAP)-carbon tetrachloride on a tetra-O-acyl-2,3,4,6-d-glucopyranose yields two anomeric oxyphosphonium chlorides (ATDP salts). One of these anomeric forms is stable and the corresponding α-hexafluorophosphate is isolable as a solid. The alcohols react with the mixture of ATDP chlorides to yield 1,2-orthoesters, while thiophenol reacts to give the thioglucoside. These results are discussed and interpreted.     

Analyse thermogravimetrique et fraudes sur les origines dans la fabrication des fromages

It has been performed a research of a quick method in order to verify adulterations in the manufacture of cheeses. In particular we have studied “Idiazabal”, produced in Basque County of the milk of “latxa” sheep, which is spread on this area. The principal and more common adulteration is caused by the mixture of sheep's milk with cow's milk, with the corresponding lost of quality. In this way, TG has been applied to several samples of probable fraudulent milk. TG and DTG curves and their respective standards bring a qualitative index of the presence or absence of cow's milk. Seeing the results, it can be deduced that the method is valid and quick for the qualitative analysis of milk mixtures.     

Etude par R.M.N. des mouvements et de la geometrie de l'ion oxonium dans des sels cristallises

Wide line P.M.R. spectra have been recorded from 90°K to room temperature for three oxonium compounds : H₃O⁺NO₃⁻ ; H ₃O⁺ClO₄⁻ ;(H₃O⁺)₂PtCl₆²⁻ and two nitrile oxonium compounds : (H₃O⁺)₂ (NO₂⁺)₉ (ClO₄⁻)₁₁ and (H₃O⁺) (NO₂⁺) (ClO₄⁻)₂.By a second moment analysis in the rigid lattice, the d_(OH) of H₃O⁺ ions are shown to decrease in the order :NO₃⁻ ⪢ ClO₄⁻ ⋍ PtCl₆²⁻ ⋍ 1.1.2. ⋍ 2.9.11.If the oxonium ion is rigid at all temperature in the nitrate,it undertakes complex motions in all the other cases.Reduction factors as well as activation energy laws at temperature under the phase transition can be interpreted as consequences of at least two uncorrelated reorientations. The order of Ea :ClO₄⁻ ⪢ PtCl₆²⁻ ⪢ 2.9.11. is characteristic of an increasing freedom of the oxonium ion.Above the phase transition, the motion is classified as endospheric and goes to an isotropic one at increasing temperatures.     

Action des phenylacetonitriles α-substitues sur les tetrahalomethanes en milieu basique: Mecanismes de l'halogenation et de la duplication

Carbanions of substituted phenylacetonitriles are halogenated by carbon tetrachloride or carbon tetrabromide, and also converted into symmetrically-substituted succinonitriles. The halogenation occurs via an ionic process, and the formation of succinonitriles via a radical process, essentially a no-chain mechanism in the case of diphenylacetonitrile anion, confirmed by the course of the reaction of p-nitrobenzylchloride on the diphenylacetonitrile anion.