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 tacticite du polychlorure de vinyle sur son comportement physique en fonction de la temperature

Three PVC samples, having syndiotacticity contents between 55 and 68%, have been prepared and characterized by previously described methods. Their thermal behaviour has been studied using three techniques, viz. inverse chromatography. ATD and Rheovibron. The results make clear the influence of tacticity on both the number and the intensity of transitions. These results are accounted for on the basis of a possible influence of TG conformations on the behaviour of the amorphous phase.     

Influence de la temperature sur les associations moleculaires et sur la polymerisation de l'acide acrylique en solution

Infra-red spectra of pure acrylic acid and solutions of monomer in toluene indicate that increasing the temperature from 20 to 60° displaces the equilibrium of H-bonded species from cyclic dimer to open oligomer. Viscosity measurements on the same solutions confirm this conclusion. In methanol solutions. alcohol-alcohol and alcohol-acid associations are found together with the acid-acid associations and the interpretation of the results is extremely difficult. Polymerization kinetics are directly influenced by the shift of association equilibria. In hexane, an increase in temperature results in a sudden increase in reaction rate as the linear oligomeric structures appear in the solution. In methanol increase in temperature reduces the kinetic anomalies observed at 20 and the polymerization no longer exhibits any stereospecificity. At the same time, a chain transfer process sets in. These various results confirm the earlier assumption of an assisted propagation step occurring in auto-associated aggregates of acrylic acid.     

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 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 l'hydrolyse des N-pyrrolylmethylene-2 anilines

Hydrolysis of the imine function of a series of Schiff bases derived from pyrrole-2-carboxaldehyde and substituted anilines (X = H, p-OCH₃, p-OC₂H₅, p-CH₃, p-Cl, p-Br, m-CN, m-NO₂, p-NO₂) was studied in all of the pH ranges. The hydrolysis curves log k_abs (mn^?1) = f(pH) were established in buffered aqueous methanol by polarography or amperometry. The shapes of the curves obtained for pH > 5 indicates that N-pyrrolylmethylene-2 anilines hydrolyse according to the same mechanism as N-benzylidene anilines. The particular stability of these products for pH < 5 permits one to obtain complete hydrolysis curves in acid media. A very good Hammett correlation (k_obs = + 1,73) has been established from the maxima which appear for strong acidity. This stability is interpreted as due to the specific electron-donating effect of the pyrrole nucleus. The influence of the structural parameter X on the morphology of the curves log k_abs = f(pH) and on the hydrolysis mechanism of the imine function is discussed in all of the pH ranges.     

Influence de la substitution et de la solvatation sur les forces acides. Approche Theorique.

The use of a theoretical method which takes account of solvent effects permits an original approach of importance of substitution and solvation on acid strengths.     

Influence de l'oxygene adsorbe sur la sulfatation de l'oxyde de nickel par le dioxyde de soufre

The interactions between gaseous sulfur dioxide and nickel oxide at 250° have been investigated by means of temperature-programmed desorption (TPD) and microcalorimetric techniques. Depending on the thermal treatment of the oxide, different NiO samples were prepared containing chemisorbed oxygen species, O¹, O², O³ and O⁴, with different energies. The calorimetric data indicated that the weakly-bound species O¹ is the most reactive of the oxygen forms towards sulfur dioxide. In this case, the TPD curves (m/e=48 andm/e=32) show a new peak at 710°; this may be correlated with the desorption of a sulfur-containing compound, probably NiSO₄, created by oxidation of sulfur according to the reaction S^IVS^VI. The regeneration of the species O¹ has been studied as a function of the temperature of oxygen adsorption; the most favourable temperature for the sulfation of nickel oxide appears to be about 400°.

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Zusammenfassung Die Wechselwirkung zwischen gasförmigen Schwefeldioxid und Nickeloxid bei 250° wurde mittels temperaturprogrammierter Desorption (TPD) und mikrokalorimetrischer Techniken untersucht. Abhängig von der thermischen Behandlung der Proben wurden verschiedene, die Sauerstoffspecies O¹, O², O³ und O⁴ mit unterschiedlichen Energien enthaltenden NiO-Proben hergestellt. Die kalorimetrischen Daten weisen darauf hin, dass die schwach gebundene Species O¹ gegenüber Schwefeldioxid die reaktivste von diesen Sauerstoffarmen ist. In diesem Falle zeigt die TPD-Kurve (m/e=48 undm/e=32) einen neuen Peak bei 710°; das kann mit der Desorption einer schwefelhaltigen Verbindung, wahrscheinlich NiSO₄, erklärt werden, die durch Oxydation von Schwefel entsprechend der Reaktion S^IVS^VI gebildet wird. Die Regeneration der Species O¹ wurde in Abhängigkeit von der Temperatur der Sauerstoffadsorption untersucht; die günstigste Temperatur für die Überführung von Nickeloxid in das Sulfat scheint etwa 400° zu sein.

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- 250° . , NiO, O¹, O², O³ O⁴ . , , O¹ - . , - (/=48 32) 710°, , NiSO₄ . O¹ . , 400°.

     

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.     

Influence de la longueur d'onde sur la photoisomerisation de derives de l'hexatriene-1,3,5

Kinetic studies of photoisomerization of 1-phenyl 6-methyl-cyclohexa-1,3-diene, and of the four isomeric 5-phenylhepta-1,3,5-trienes, have been performed at 313, 254, 228 and 214 nm. Photoreactions of these compounds are dependent on the wavelength of irradiation. Photolysis at short wavelength of Z,E-5-phenylhepta-1, 3,5-triene initiates a new reaction, sigmatropic [1,5] hydrogen migration, forming an ene-allenic compound. Thermal reactivity data for polyenic compounds supports the assigned structures.     

Influence de la tension de vapeur sur une transition de phases et un equilibre peritectoide

The compound As₄Se₃ exhibits two polymorphs, α andβ. The latter undergoes a peritectoid decomposition. The two phenomena require a vapour pressure action. They are both explained on the basis of aT- V- x diagram. Two cases are described. In the first hypothesis, no solid solution exists. The second hypothesis implies two solid solutions for the two forms α andβ. A comparative study of these two cases has been made. The existence of two invariant planes has been shown in the second case, which makes it rather different from the first one.     

Polymerisation cationique de l'indene amorcee par le tetrachlorure de titane-II Influence de la temperature sur la vitesse de polymerisation

Polymerization rates in the indene-titanium tetrachloride-methylene chloride system, using rigorously dried reagents, have been measured at various temperatures. At sufficiently high temperatures (above ?10°C), polymerization yields may be incomplete and cocatalytic phenomena have been observed; at low temperatures, yields are always complete. The reaction order in monomer is unity at ?70°C, which may be explained by a constant concentration of active centres during the major part of the reaction. At ?70°C, the reproducibility shows that residual water has no cocatalytic effect. The measured values of polymerization initial rates at various temperatures show that the apparent overall activation energy is negative. Various interpretations of this result are discussed, but it may be more easily reconciled with both the existence of a quasi-stationary state and an equilibrium between different types of active species.     

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 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 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.