Oligomérisation anionique de l'ethylène. II. Etude des paramètres thermodynamiques

A kinetic study, as a function of temperature, of ethylene oligomerization by the n-BuLi–TMEDA complex allowed us to evaluate the thermodynamic parameters (ΔS^? < ?23.7 u.e.) and thus to support a transition state where the ethylene is coordinated to the lithium atom.     

Oligomérisation anionique de l'ethylène. III. Application à la synthèse d'alcools à longue chaine

Living oligomers of ethylene obtained by n-BuLi complexed with TMEDA have been deactivated by ethylene oxide. The nuclear magnetic resonance study of the product obtained allowed us to follow the influence of TMEDA toward the functionalization. Three products have been characterized: By increasing the ratio [TMEDA]/[n-BuLi] one obtains a decrease of the functionalization reaction.     

Polymérisation anionique des diènes. III. Etude thermodynamique de la propagation du butadiène et de i'isoprène par les organo-alcalins

The present work is concerned with the influence of the polymerization temperature on the propagation mechanisms of polyisoprenyl- and polybutadienyl-alkali metals. The thermodynamic parameters of the contact ion pairs and free ions propagations have been calculated. With Li⁺ in dioxane solvent, the vinyl propagation is stereospecific (for isoprene, the propagation is mainly 4–3). In comparison with benzene, the vinyl propagation of the polydienyl-Li contact ions pairs should be due to complexation of Li⁺ by dioxane, an electron donor having a weak dielectric constant. In general, the stereospecificity of the propagation of contact ion pairs decreases with increasing counterion size; little difference has been observed with K⁺ and Cs⁺ ion pairs in dioxane and benzene media. For isoprene, the methyl substituant should have chiefly a steric effect in the propagation of free ions, whereas it should confer a polar character to the isoprene molecule in the presence of ions pairs.     

Polymérisation “basse pression” de l'ethylène en préasence de noir de carbone

The polymerization of ethylene with Ziegler-Natta catalysts in the presence of carbon black has shown three characteristic features both with a heterogeneous catalyst, AlBu₃? TiCl₄, and with a soluble catalyst, Cl₂Ti(C₅H₅)₂? AlEt₂Cl. They are, in order of increasing importance: reactivity of the organoaluminum derivatives with surface chemical groups of the carbon black, adsorption of a certain amount of organoaluminum compounds on the carbon black surface, and influence of the specific surface of carbon black, which controls the dispersion degree of the catalytic system. Furthermore, it was possible to obtain polyethylene by this procedure, containing different amounts and different types of carbon black.     

Polymérisation anionique des diènes. VI. Microstructure des polybutadiène et polyisoprène par résonance magnétique protonique à 250 MHz et mécanismes de propagation

Analysis by 250-MHz proton magnetic resonance (PMR) allows more precise examination of the microstructure of anionic polyisoprenes and polybutadienes obtained in the presence of organo-alkali metals. Besides vinyl addition, the propagation of contact ion pairs in dioxane solvent gives a mixture of cis and trans products with isoprene, whereas only trans product is obtained with butadiene. The presence of 1,4-trans-polyisoprene appears to be inconsistent with the cis configuration of the polyisoprenyllithium living end in dioxane or tetrahydrofurane media. In taking into account the existence of complexation phenomena, it was suggested that propagation mechanisms should involve a transition state which should begin with the trans configuration before isomerization into the more stable cis configuration. For the free ions, the living end of the carbanion should be entirely trans.     

Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité

With accumulated HR-NMR spectra of anionic polyisoprenes, it has been possible to study the influence of the nature of the propagating species on the microstructure of the obtained polymers If free ions are responsible for the propagation, the microstructure (1,4-: 25%, 1,2-: 33%, 3,4-: 42%) does not depend on the nature of the cations. But with contact ion pairs, the different addition modes are governed by the size of the alkali metal counterions. Mechanisms of anionic propagations via diene–cation coordination are proposed.     

Etude cinétique de l'ouverture du cycle Δ2 imidazoline par hydrolyse basique

The kinetics of base hydrolysis of two Δ₂ imidazolines were followed by uv spectroscopy in sodium hydroxide and in carbonate buffers. In the most basic medium the rate of hydrolysis is independant of pH. This is explained if the rate determining step is attack of hydroxide ion on the protonated form of the substrate. In less basic medium there is a change in the slow step, the breaking of the intermediate becomes rate determining.     

Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité. II. Influence de la nature du solvant

The present work reports some new results on the dependence between the stereospecificity of the anionic propagation of isoprene and the nature of the active centers. The stereospecificity of the propagation of macroheterobicylce separated ion pairs does not depend on the nature of the alkali counterions, and the microstructure of the polyisoprenes obtained does not differ from that of those produced by free ions. Variations in the microstructure were observed in the propagation of contact ion pairs, depending on the nature of the cation and the solvent used. These variations are likely to be related to the degree of intimacy of the contact ion pairs. There are two main factors which affect the stereospecificity of the propagations in different ways: the size of the cation and the donating power of the solvent. Finally, the external solvation of the propagation ions pairs was confirmed by the microstructure of polyisoprenes synthesized in mixed (inert + donor) solvents.     

Etude cinétique comparée de la substitution nucléophile de quelques chloro-2 pyridines condensées

A comparatie kinetic study of nucleophilic substitution of some condensted 2-chloropyridines by piperidine was carried out and an “autocatalytic effect” was observed in the case of 1-methyl-4-chloro-5-azaindole. The rate constants of such substitutions were determined for 1-methyl-4-chloro-5-azaindole, 4-chlorofuro[3,2-c]pyridine, 1-phenyl- and 1-benzy;(1H)pyrazolo[4,3-c]pyridines, 4-chloro-6,7-dimethylpyrrolo[2,3-d]pyrimidine, and a classification of reactivity of these compounds, as compared to 2-chloropyridine, was established.     

Polymérisation anionique des diènes. IV. Contribution aux etudes des mécanismes de propagation stéréospécifique des isoprène et butadiène par les organo-alcalins

By taking into account different possible interactions between the living end, the counterion and the nature of the solvent used on the one hand, and the influence of the temperature on the kinetics and the microstructures of polydienes on the other hand, it has been possible to suggest some new explanations concerning the mechanisms of the anionic propagation of butadiene and isoprene. In hydrocarbon media, the stereospecificity of the 1,4 propagation initiated by lithium should be considered as the consequence of the coordination of the counterion by both of the two bonds of the diene molécule. The stereospecificity of the vinyl propagation by the same counterion in dioxane solvent should be the consequence of the competition between the (Li⁺, dioxane) and (Li⁺, diene) coordination complexations. In this case, the Li⁺ counterion should only be coordinated by only one of the two double bonds of the diene molecule. With isoprene, the π-electron donation should originate mainly from the C₃?C₄ double bond. The decrease of the stereospecificity is due to the increasing size of the alkali counterion and the separation or the dissociation of the growing ion-pairs.     

Catalyseurs Ziegler-Natta supportés sur MgCl2 pour la polymérisation du propène. I. Etude de la réaction entre le triéthylaluminium et le benzoate d'ethyle

In this article we describe a study of the reaction between triethylaluminium (TEA) and ethylbenzoate (BE) in a heptane solution by Fourier transform, infrared (IR), and ultraviolet (UV) spectroscopy. These compounds were chosen as a model of the cocatalytic solution used with a Ziegler-Natta catalyst supported on MgCl₂ for the stereospecific polymerization of propene. In the polymerization concentration range a 2 TEA:1 BE yellow complex was added to the solution and no free BE could be detected at a AI/BE molar ratio above 2: the solution contained only free and complexed TEA. The complex decomposed spontaneously to a colorless aluminium alcoholate. The rate of decomposition remained slow at room temperature and the reaction was enhanced by heating or by a high AI/BE ratio or high AI concentration. The decomposition was inhibited in the presence of an olefin.     

Etude par Résonance Magnétique Nucléaire de dérivés phosphores. Etude de dithiaphospholanes-1,3,2

The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two ³J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the ³J(HH) values, the torsion about the C₄—C₅ bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.     

Etude cinétique des effets de fluence énergétique,de débit de fluence,et d'effacement induits par des ions lourds et des photons γ dans le triacétate de cellulose

The kinetic interpretation of the damage produced by heavy ions (Kr and Cl from 1 MeV/amu) and γ radiation in cellulose triacetate leads to an exponential dependence on the ion fluence. A comparison of the fading effect produced by heavy ions and γ rays shows that the heavy ions, unlike γ rays, cause irreversible damage. Finally, a nonlinear dependence on the flux of ions and γ rays is found in the kinetics of radiation damage. This result is contrary to the usual assumption that heavy-ion flux, like γ-ray flux, is additive, at least for the fluxes of 10⁹?2 × 10¹⁰ ions/cm²s and dose rates of 10³–10⁴ Gy/h used in this work.     

Polymérisation anionique de i'isoprene et du butadiene en presence d'agents complexants

With the aid of DCHE and [222], solutions of sodium, potassium, rubidium, and cesium have been prepared in tetrahydrofuran (THF) and in benzene. All these new species initiate the polymerization of butadiene and isoprene avoiding the inconvenience of heterogeneous reactions. The presence of free ions and/or complexed ion pairs allows the increase of vinyl structures even in benzene.     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Etude cinétique de la réaction de bromation d'anisoles monosubstitués. Transmission des effets électroniques et caractéristiques de l'état de transition

Reactivity-structure correlations for anisole and eleven of its substituted derivatives established from bromination rate constants in liquid SO₂, unlike observations in water, show the reaction to be highly sensitive to substituent effects, (ρ = ?7.1; ρ = ?10.51). This result is ascribed to the solvation of the methoxy group which decreases the conjugation of para-substituted (ρ = ?9.70) compared to that of ortho-substituted derivatives (ρ = ?8.86). The highly solvated transition state lies far from reactants on the reaction coordinate and the positive charge developed in this state is nearly unity.