Influence des effets de substituants sur la protonation de la pyridine

Standard thermodynamic values of proton ionisation of 3 substituted (Cl?, Br?, I?, C₂H₅? and CH₂CN?) pyridine derivatives are determined at 25°C, in an aqueous medium of ionic strength 0.5 M KNO₃.Free energies are deduced from equilibrium constants log K potentiometrically calculated. Enthalpies are obtained from calorimetric measurements.ΔG^o, ΔH^o and ΔS^o values are discussed in the context of the results of our earlier studies on this subject.The Hammett plot corresponding to the thirteen systems examined gives the proton ionisation constant of a substituted pyridine from the equation log K = 5,48 – 5,94Σσ.Besides, a linear relationship is found between ΔG^o and ΔH^o, which confirms the observation made previously in other series of pyridine derivatives.     

Influence de la structure sur les proprietes mesomorphes des polyesters—II

Several new thermotropic liquid crystalline polyesters have been synthesized. The influences of various rigid, mesogenic parts of the macromolecule on the transition temperatures have been studied.     

Influence de la structure sur les proprietes mesomorphes des polyesters—I

A new series of thermotropic liquid crystalline polymers has been synthesized. Mesogenic elements are separated by flexible spacers —(CH₂)_n— in the backbone. The thermal properties of these polymers are analogous to liquid crystals.     

Influence de la structure cristalline sur la décomposition thermique des hydroxynitrates de métaux bivalents: Exemple des hydroxynitrates de cadmium

The solid solid equilibria in the binary system Ca₃(PO₄)₂-CaNaPO₄ have been studied. Different diagrams have been proposed for this system. The differences relate to the limits of the field of existence of a non-stoichiometric phase (phase A) stable at high temperature and undergoing eutectoid decomposition during cooling; they can be explained by the existence of two metastable equilibria diagrams which are superposed in the stable diagram. These metastabilities depend on both the cooling rates and the maximum temperatures reached before this cooling.

---

Zusammenfassung Fest fest Gleichgewichte des binären Systems Ca₃(PO₄)₂-CaNaPO₄ wurden untersucht. Verschiedene Diagramme wurden für dieses System vorgeschlagen. Diese Unterschiede beziehen sich auf die Grenzen des Existenzbereiches einer nichtstöchiometrischen, hochtemperaturstabilen Phase (Phase A), die sich beim Abkühlen nach einer eutektoiden Reaktion zersetzt; sie können durch die Existenz von zwei dem stabilen Diagramm überlagerten metastabilen Gleichgewichtsdiagrammen erklärt werden. Diese metastabilen Zustände hängen sowohl von der Abkühlungsgeschwindigkeit als auch von den vor dem Abkühlen erreichten maximalen Temperaturen ab.

---

Ca₃(PO₄)₂-CaNaPO₄ — . . / A/, , - , , . , , .

     

Influence de la temperature et du gradient de vitesse sur la viscosite des solutions diluees de xanthane

The dependence of the relative viscosity of a dilute xanthan solution (0.4 g·l^?1) has been studied as a function of temperature (20–70°) and of the ionic strength of the solvent. When the rate of shear exceeds 100 sec^?1, the viscosity can be expressed as γ̊ the exponent (n ? 1) varies with the polymer conformation. In aqueous solution in the absence or in the presence of added salt at a temperature above the melting temperature T_M (depending on the ionic strength of the solvent), the exponent (n ? 1) is ?0.285 and corresponds to the unordered conformation; at temperatures below T_M, the local helical conformation is rigid and (n ? 1) is ～ ?0.44 almost independent of the temperature.     

Influence de la structure sur les proprietes mesomorphes de polyesters—III

A new homogous series of thermotropic mesomorphic polyesters with high inherent viscosity has been synthesized. Mesogenic elements

are separated by flexible spacers CO(CH₂)_nCO in the backbone. A study of their mesomorphic properties is reported.     

Influence de la conformation des polyions sur la fixation de colorants—III. Etude de la fixation de l'auramine o sur des polyacides synthetiques par equilibres de dialyse

The binding of auramine O (AuO), a cationic dye which does not dimerize, to poly(methacrylic acid) (PMA) and poly(acrylic acid) (PAA) has been measured by dialysis experiments. The effects of ionization, ionic strength and polymer to dye ratio (P/D) have been systematically investigated. At low ionization and P/D = 100, the bound fraction (q) of AuO is distinctly higher with PMA than with PAA at all ionic strength; this difference can be attributed to non-electrostatic interactions. Increase of ionic strength leads to displacement of the bound dye; on the other hand, high P/D ratio favours binding. We were able to describe the binding isotherms by an ion-exchange process at constant ionization and ionic strength. Water-methanol mixtures, known to destroy the coiled conformations of PMA, lead to a decrease in q; the same is observed in unionized acidic PMA solutions where ionic interactions are suppressed. These results indicate a strong binding due to the insertion of the dye into the polyion compact core and also a weak electrostatic one; they agree with the observations of spectrofluorescence; it must be emphasized that the bound fraction of dye is not, in itself, a significant parameter of conformational states.     

Effet de structure sur la reversibilite de la condensation aldolique: Reaction des phosphonoesters et du benzaldehyde

For the reaction between benzaldehyde and phosphonoesters or nitriles, the formation of oxyanionsRS,RS is much more reversible starting from phosphonoesters than from nitriles. These anions are precursors of Z olefins. The stereoselectivity of the reaction is interpreted.     

Addition des ylures de carbonyle derives de gem-dicyanoepoxydes sur les benzylidene anilines substituees

The reaction of substituted benzylidene anilines with 1,1-dicyano or 1-cyano 1-ethoxycarbonyl epoxides gives oxazolidines, the structures of which is established by NMR spectroscopy. The formation of oxazolidines proceeds via regiospecific addition of epoxide derived ylid to imine. The influence of ylid substituants and imine substituants on the reaction may be interpreted by interactions of the frontier orbitals.     

Influence de la complexation sur le transfert des cations en osmose inverse

The influence of complexation by different ligands on the transfer of metallic cations in reverse osmosis has been studied by using membranes composed of aromatic polyamides. In spite of the large volume increase of the diffusing solute, the addition of a complexant can significantly improve the transfer of metallic cations through a reverse osmosis membrane. The most important factor in the improvement of the transfer is the solubility in the membrane of the complexes created. This solubility is linked to the possibility of creating hydrogen bonds between the membrane and the complex. Moreover, the addition of substances which strongly solvate both the membrane and the solute leads to an improvement of transfer which increases considerably with the increasing pressure. These results suggest the possibility of separating metal cations by specific complexation.     

Influence de la solvatation preferentielle sur les dimensions des polymeres en solution dans des melanges de solvants

We have studied the dependence of the intrinsic viscosity number of polymers on the composition of binary solvents. The systems studied are: polystyrene in CCl₄/CH₃OH, C₆H₆/CH₃OH and C₆H₆/heptane and poly-2-vinylpyridine in CHCl₃/CH₃CH₂OH. We have also studied, for the same systems, preferential solvation of the polymers, using light scattering.We have observed that, near the θ point, short polystyrene chains exhibit a higher expansion than long chains. This was explained in terms of the dependence of preferential solvation on molecular weight.For the system poly-2-vinylpyridine/CH₃CH₂OH/CHCl₃, we have established the viscosity increment dependence on solvent composition. The curve describing this increment differs markedly from the theoretical curve based on G^E values (excess free energy) of the solvent mixture. However, taking into consideration the process of preferential solvation, the experimental curve can be corrected and becomes very similar in shape to the theoretical curve but there still remains a quantitative difference between the two curves.     

Ions α-cetocarbenium. Influence de la structure sur l'evolution des ions α-cetocyclohexylcarbenium

α-Ketocyclohexylcarbenium ions are formed by dehalogenation in HgSbF₆Ch₂Cl₂ of the corresponding α-bromo carbonyl compounds 6,7, 8 and 9. In this medium they lead principally to bicyclic oxonium salts, the structure of which depends on the group adjacent to the carbonyl group, and positions of ring substituents. By a suitable choice of Y, it is possible to “functionalise” an α-keto cyclohexane system in either 3 or 4 positions.     

Etude de l'action de la pression sur la pression osmotique des solutions de polymeres

Osmotic pressures of solutions of polymers were measured as a function of pressure. The measurements were made at room temperature at pressures up to 500 bars. The results are as follows:

•

-the effect of pressure depends upon the polymer-solvent pair. Depending upon the particular case the effects can be positive, negative or zero. We have given examples for each case.     

Amelioration des separations chimiques sur resines echangeuses d'ions: Influence de la granulometrie

In order to reduce the time requirement for ion exchange separations the kinetics of the elution of different ions was studied in the function of the grain size of the ion exchange resins. Using a counter current apparatus seven differents fractions could be separated in the case of commercial resin Dowex 1×10 and 50 W×12. Grain size was found to have a great influence on the shape of the elution curves. The finer and more homogenous the resins are the sharper are the peaks on the elution curves. These consderations were utilized for the separation of rare earth, alkaline and alkaline earth metals, respectively.      

Influence de la conformation sur le champ de force etles modes de vibration des monohalogénocyclohexanes

Valence force fields and normal modes of vibration of axial and equatorial forms of four monohalogenated cyclohexanes are computed and compared. A new assignment of axial isomers and of the equatorial form of fluorocyclohexane is proposed. Both geometry and force field differences are necessary to explain rotational isomerism splittings. Normal modes of equatorial isomers are rather close to those of cyclohexane. Interactions between non-bonded atoms are found for the axial isomers.     

Adsorption d'eau sur la kaolinite: Influence de la nature des sites actifs

Water adsorption on kaolinite is a specific cooperative adsorption which does not satisfy the fundamental hypothesis of the BET theory.The adsorption isotherms on different homoionic samples show the effect of the hydration energy of the active sites (exchangeable cations) on quantitative adsorption data.The corresponding calorimetric curves present a maximum which characterizes interactions in the adsorbed phase. A relationship is apparent between these interactions and the electric field or the polarizability of the fixed cation, these factors determining the nature of the bond between the surface and cation.From the experimental data, we may propose an approximative value for the number of molecules which compose the primary hydration sheath of the active sites.     

Effet de la temperature sur la structure cristalline d'un biocorail

Coral is a natural biomaterial used nowadays frequently in medical applications. Our recent studies show that a coral implanted in bone tissue is gradually transformed to become a neoformed bone. In some special cases, high temperature has to be used as sterilization mean instead of gamma or electron irradiations. Here, we perform this method and we analyse cristalline behaviourvs. temperature with X-rays diffractions. We show that coral aragonite and mineral pure aragonite have two different temperatures for aragonite-calcite phase transition: 300° and 470°C.However until 200°C and under atmospheric pressure, any transformation are observed at macroscopic scale.

---

Zusammenfassung Korallen sind ein natürliches Biomaterial, welches heute oft medizinisch angewendet wird. Unsere jüngsten Untersuchungen zeigen, daß im Knochengewebe implantiertes Korallenmaterial nach und nach in neugeformtes Knochengewebe umgewandelt wird. In einigen speziellen Fällen müssen anstelle von Gamma- oder Elektronenbestrahlung hohe Temperaturen zur Sterilisierung eingesetzt werden. Diese Methode wurde hier angewendet und mittels Röntgendiffraktion das kristalline Verhalten in Abhängigkeit von der Temperatur analysiert. Es wurde gezeigt, daß Korallen-Aragonit und mineralisches reines Aragonit für die Aragonit-Kalzit Phasenumwandlung zwei verschiedene Temperaturen aufweisen: 300° und 470°C.In allen Fällen werden bis 200°C und unter Normaldruck Umwandlungen makroskopischen Ausmaßes beobachtet.