Études calorimétriques en milieu solvant organique IV. Dissociation de LiAlH4 dans le tétrahydrofuranne

From calorimetric measurements a model of solution is proposed for LiAlH₄ in THF. It is ionised as LiAlH₄ ? Li⁺ + AlH^?₄. For this reaction, ΔH_i = 3.05 kcal mol^?1 and the dissociation constant is K = 0.11.     

Études calorimétriques en milieu solvant organique: II Enthalpies de dissolution et de dilution du boranate de lithium (LiBH4) et de l'alanate de lithium (LiAlH4) dans le tétrahydrofuranne

The enthalpies of dissolution and dilution of LiBH₄ and LiAlH₄ in THF have been determined.Dissolutions are exothermic. The endothermic dilution of LiAlH₄ suggests for this compound, either a dissociation or an association equilibrium.     

Études calorimétriques en milieu solvant organique I. enthalpie de dissolution du bromure de lithium dans le tétrahydrofuranne

A calorimeter has been devised to determine heats of solution in the absence of air. The enthalpy of solution of lithium bromide in THF has been measured at different concentrations. The results do not show a large difference with the heat of solution in water.     

Decomposition de l'acide peroxydodecanoique dans CCl4 : role du solvant

The decomposition of peroxydodecanoic and in refluxing CCl₄ proceeds by a complex process involving ionic and radical reactions. In the latter, this study has confirmed the important role, shown previously,¹ of the character(nucleophilic or electrophilic) of the radical on the regioselectivity of the attack on the peracid.     

Reactions en milieu heterogene solide-liquide faiblement hydrate III: La reaction de wittig dans le systeme carbonates alcalins/solvant organique protique

The use of alkaline carbonates in a slighty hydrated solid-liquid protic organic media allowed the synthesis of alkenes from polyfunctionnal aldehydes with high yield in a E preferential stereochemistry specially with non-stabilized ylides. It has been shown that the decomposition of the threo betain acts as the determining step of the reaction.     

Études calorimétriques en milieu solvant organique: III. Enthalpie de dilution de l'alanate de lithium LiAlH4 dans le tétrahydrofuranneen présence d'halogénure de lithium

Heats of dilution of lithium aluminum hydride in THF, in THFLiBr and in THFLiCl have been established. At a constant concentration of LiBr in THF, dilution of LiAlH₄ is exothermal, and consequently it is shown that lithium aluminum hydride is dissociated in THF.     

Polymerisation anionique de l'acroleine—I. Polymerisations amorcees par des organo-sodiques dans le tetrahydrofuranne

In tetrahydrofuran, with Na⁺ as counter-ion, the anionic polymerization of acrolein involves numerous transfer reactions to monomer and to polymer; on the other hand, termination of growing chains does not occur. The use of initiators, like carbanions or oxanions, does not affect the polymerization rate. The kinetic order of the reaction is unity for monomer and unity for initiator; these results indicate that the living ends are not associated at the studied concentrations of initiator. Without stating precisely the mechanism of the transfer reactions, we have proposed a kinetic scheme.In tetrahydrofuran, with Na⁺ as counter-ion, the anionic polymerization of acrolein involves numerous transfer reactions to monomer and to polymer; on the other hand, termination of growing chains does not occur. The use of initiators, like carbanions or oxanions, does not affect the polymerization rate. The kinetic order of the reaction is unity for monomer and unity for initiator; these results indicate that the living ends are not associated at the studied concentrations of initiator. Without stating precisely the mechanism of the transfer reactions, we have proposed a kinetic scheme.     

Reactions de l'acide perchlorique avec le phenylacetylene en solvant acide acetique anhydre

Perchloric acid in acetic acid reacts with phenylacetylene to give acetophenone, α-chloroacetophenone, α,α'-dichloroacetophenone, α-acetoxy α'chloroacetophenone, dichloro-styrène and chlorophenylacetylene. Kinetics of these reactions have been established.     

Polymerisation du methacrylate de methyle par le chlorure de tertio-butylemagnesium en solution dans le tetrahydrofuranne—I Etude de l'equilibre de dissociation du chlorure de tertio-butyle-magnesium

The thermodynamics of the dissociation of tBuMgCl have been carefully studied by PMR taking into account the exact concentrations of the various components. The Schlenk equilibrium should mainly be governed by the formation of different complexes for which degrees of solvation depend on the Grignard concentration. Owing to the estimated values of ΔH and ΔS, at low temperature in THF. MgCl₂ precipitates and only the symmetrical form tBu₂Mg initiates the polymerization of methylmethacrylate.     

Dosage de l'hydrogene,de l'azote et de l'oxygene dans le monocarbure d'uranium

A method is described for the determination of hydrogen, oxygen and nitrogen in uranium monocarbide. Hydrogen and oxygen are determined by the classical or modified “Platinum flux” method at 2000° with a coefficient of variation of 10%. Nitrogen is determined at 2000° by the modification of the “Platinum flux” technique. The results obtained are in agreement with those found by Kjeldahl analysis. The coefficient of variation is about 10%. A procedure for the simultaneous determination of the 3 gases is given.     

Comportement de LiAlH4 en fonction de la dilution dans la racemisation d'un silane optiquement actif en milieu thf

The optically active methylphenyl-α-naphthylsilane racemises quickly in tetrahydrofuran in the presence of LiAlH₄.Kinetic results show a different behaviour of the hydride depending on its concentration. Activation parameters have been obtained and mechanisms proposed.     

Polymerisation radiochimique de l'acide acrylique en solution dans l'alcool isopropylique et le dimethylformamide

The radiation-induced polymerization of acrylic acid in isopropyl alcohol and dimethylformamide solutions was investigated between?196°and40°. Mixtures which form glasses at low temperatures exhibit a maximum in the rate of polymerization at 30° and 50° above the glass transition temperature (T_g). The difference between the most favourable temperature for polymerization and T_g is larger than in systems studied previously. This fact could be due to the presence of H-bonded aggregates.The study of the polymerization of acrylic acid in dimethylformamide solution at 20° led to a correlation between this reaction and the presence of plurimolecular aggregates. The very high polymerization rate and the syndiotacticity of the resulting poly(acrylic acid) confirm the earlier assumption of a favourable orientation for propagation of the molecules of acrylic acid in these aggregates.     

Comparaison entre le role de l'eau et celui d'un ether couronne dans le cadre de la reaction de wittig realisee en milieu heterogene : liquide-solide

The similar results issued from the use of water and the 18-crown 6 ether for the Wittig reaction (in liquid-solid two-phase systems) allowed us to obtain very high yields in olefin starting from aromatic as well as aliphatic aldehydes.     

Etudes dans le domaine de l'autoxydation—III : L'autoxydation de cyclopentadienones en milieu basique

Even though they do not possess an acidic hydrogen, cyclopentadienones (cyclones) may be autoxidized under basic conditions. The mechanism involves in the first step a Michael addition of base, giving a carbanion which is autoxidized. The resulting lactol undergoes a fragmentation reaction with base, confirming the proposed structure.     

Substitutions nucleophiles d'amines sur les halogeno-1 cycloalcenes en presence de bases dans le tetrahydrofuranne

Condensations of amines with 1-chloro cycloheptene in the presence of complex base (NaNH₂-t-BuONa) lead to mixtures of enamines and 1,2-cycloheptadiene dimer. Under the same conditions, 2-chloro and 3-chloro bicyclo [3.2.1] oct-2 enes yield only enamines via bicyclo [3.2.1] oct-2 yne. The mechanism of these reactions depends not only upon the halogeno derivatives but also upon “reaction media.” The general problem of the interpretation of elimination-addition reactions is discussed.     

Polymerisation cationique de l'indene amorcee par le tetrachlorure de titane-I Influence des impuretes du solvant,le chlorure de methylene,et effets cocatalytiques de l'eau et de l'acide chlorhydrique

The polymerization of the system indene-titanium tetrachloride-methylene chloride gave irreproducible kinetics which have been attributed to variable concentrations of impurities in the solvent. Incomplete yields sometimes observed at ?70° are also caused by impurities, but introduction of water and hydrochloric acid then gives complete yields. A new method of solvent purification has been used giving reproducible yields and rates. In such cases, monomer consumption at ?70° follows the rate law log [M]_o/[M] = kt.