Effets de micelles cationiques sur l'hydrolyse alcaline d'acetanilides a groupe acyle active par des substituants electro-attracteurs

Micellar effects of CTAB upon the alkaline hydrolysis of CF₃-CO-N(CH₃)C₆H₅, CHCl₂-CO-N(CH₃)C₆H₄X and CH₂Cl-CO-N(CH₃)C₆H₄X, (X=p-OCH₃H,p-Cl) are reported. Variations of k_obs, and of kinetic order of the reaction with respect to HO^? ion, are interpreted as an acceleration of HO^?-catalyzed steps, and a decrease of catalysis by water for decomposition of tetrahedral intermediates; these two effects oppose each other in HO^? and H₂O catalyzed steps. Differences between micellar and DMSO effects suggest a very small local concentration of HO^? ions in micelles.     

Influence des solvants sur les associations moleculaires et sur la cinetique de polymerisation de l'acrylonitrile. Precisions supplementaires sur l'“effet de matrice”

The polymerization of acrylonitrile is auto-accelerating in bulk and in solvents which do not dissolve the polymer. The “auto-acceleration indexes” remain almost constant in these systems. Trichloracetic acid, a very polar solvent, leads however to linear conversion curves. An earlier assumption is confirmed according to which auto-acceleration is not caused by non-stationary conditions but by an oriented association complex between the monomer and the polymer arising at the beginning of the reaction (“matrix effect”). DMF, a solvent for polyacrylonitrile, seems to produce a similar effect. The disappearance of auto-acceleration in DMF solutions was explained until now by the disappearance of the perturbation of the reaction connected with polymer precipitation (“occlusion effect”). Linear conversion curves were obtained, however, in 60% DMF solutions in which the polymer still precipitates. A detailed study of post-polymerization confirms the above interpretation. It is shown that auto-acceleration remains unaltered in the presence of solvents which swell polyacrylonitrile, such as acetonitrile or small amounts of DMF, whereas post-polymerization (caused by occluded chains) is strongly reduced. Moreover, a marked post-polymerization is observed in the presence of trichloracetic acid, demonstrating the presence of long-living chains in a system which gives rise to linear conversion curves. The association of acrylonitrile with numerous solvents is investigated; it is shown by swelling measurements that polyacrylonitrile associates with its monomer.     

Étude de l'effet de quelques facteurs sur les caractéristiques de fixation du potassium et du rubidium sur l'acide antimonique,en milieu nitrique

Study of the effect of various factors on the retention characteristics of potassium and rubidium by antimonic acid in nitric acid.The effects of the concentration of alkali metal ions, the amount of antimonic acid and the concentration of nitric acid on the retention of potassium and rubidium by antimonic acid have been studied. Different phenomena govern the retention mechanism of potassium and rubidium, under the experimental conditions of this study. The difference between the retention characteristics of the two elements appears from the different shapes of the curves showing their distribution coefficients and their uptake as functions of the various factors studied. Infrared spectroscopy of the antimonic acid and its deuterated compounds showed the presence of several types of OH groups which can be distinguished by the strength of their hydrogen bonds. Rubidium is probably retained on the most accessible exchange sites, forming weak bonds, while potassium could form stronger bonds with the Sb—O groups.     

Influence des associations moleculaires sur la copolymerisation de l'acide acrylique avec l'acide methacrylique et avec l'acrylate de methyle

The copolymerization of acrylic acid with methacrylic acid in bulk is investigated at 40 and 60°. It is confirmed that a “matrix effect” occurs only for high contents of acrylic acid. The critical concentration beyond which the matrix effect disappears is shifted towards lower acrylic acid contents for higher temperatures. The copolymer composition is independent of temperature. The copolymerization of acrylic acid with methyl acrylate is investigated in a mixture which determines an “exaltation of the matrix effect” in the homopolymerization of acrylic acid (molar fractions: m_Monomers = 0.34; m_n-Hexane = 0.52; m_Methanol = 0.14). The resulting copolymers are found to contain a much larger fraction of acrylic acid residues than the copolymers formed in bulk or in toluene or DMF solutions.     

Influence des solvants sur la copolymérisation de l'acrylamide avec l'acrylonitrile

The copolymerization of acrylamide with acrylonitrile was investigated in various solvents, which can be put into three groups according to their influence on molecular associations; (1) solvents autoassociated by hydrogen- bonds (acetic acid, methanol, water, dimethylformamide); (2) polar solvents which can associate with the NH group of acrylamide (acetonitrile, dioxane, acetone); (3) inert solvents (toluene, benzene, hexane). The reaction kinetics and the compositions of the copolymers are different for each group of solvents. The composition of copolymers formed in solvents of group 1 vary widely, depend- ing on the solvent. Copolymers formed in all solvents of group 2 have the same composition which is that of copolymers formed in bulk. The amount of acrylamide is highest in copolymers formed in inert solvents of group 3. Such parameters as the degree of conversion, the reaction temperature, the mode of initiation and the extent of dilution only slightly affect the composition of copolymers. Homopolymerizations of acrylamide and acrylonitrile were investigated in all solvent used.The results suggest that the effects of solvents on the copolymerization of acrylamide with acrylonitrile are consequences of the various modes of molecular association of acrylamide. The solvents affect the equilibrium between auto- association of acrylamide and its association with solvent and thereby affect the reactivity of the monomer.     

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.     

Influence des interactions de torsion dans les reactions d'addition sur les cyclohexanones. interpretation generale du deroulement sterique des reactions des hydrures ou des organomagnesiens sur les cyclohexanones

The addition of allyl and butenyl Grignard reagents to 4-t-butylcyclohexanone affords a greater proportion of the equatorial alcohols than is formed from the corresponding saturated Grignard reagents (propyl and s-butyl). In the case of the allyl Grignard reagent, the equatorial alcohol is the major product. Lithium aluminium hydride reduction in ether at 0° of cis and trans 4-t-butyl-2-methyl-cyclohexanone and cis and trans 4-t-butyl-2-chlorocyclohexanone affords mixtures of epimeric alcohols in ratios of equatorial to axial OH 8.4:1, 20:1, 4.2:1, and >70:1 respectively. These results fit in well with the view that polar interactions and torsional strain are both important in determining the steric course of the reaction.     

L'importance de la presence de l'oxygene en position-7 dans les reactions des alkylmagnesiens secondaires avec les anhydrides tricycliques pontes.

The reaction of secondary alkylmagnesium bromides with endo and exo bicyclo-[2.2.1]hept-5-ene-2,3-dicarboxylic anhydrides lead at the corresponding ketoacids whereas with the 7-oxa exo bicyclo[2.2.1]hept-5-ene-2,3 dicarboxylic anhydride produced only the monosubstituted lactones.     

Etude des reactions de substitution homolytique sur le noyau pyridinique; influence de l'acidite du milieu

Homolytic substitution by the l-n-undecyl radical at positions 2 and 4 of the pyridine nucleus results from thermal decomposition of dodecanoyl peroxide in acetic acid. Rate dependence on pH shows that pyridine protonation increases the rate of addition of the alkyl radical to the pyridine ring but decreases the rate of the reaction of the intermediate radical with the peroxide. Results are interpreted in terms of orbital interaction theory.     

Influence de la temperature sur les manifestations de l' “effet de matrice” dans la polymerisation de l'acide acrylique en solution

This study is concerned with the influence of temperature on the kinetics of the polymerization of acrylic acid dissolved in dioxane or toluene and on the type of molecular association complexes present in these solutions. In dioxane solutions, an increase in temperature destroys the oligomeric auto-associations of acrylic acid and gives rise to monomer-solvent associations. Simultaneously, the consequences of the “matrix effect” (auto-acceleration and stéréospecificity) become less pronounced. In contrast, in toluene solutions, an increase in temperature converts the cyclodimeric auto-associations of the monomer into linear oligomers and the consequences of the matrix effect appear (or become more pronounced). The Arrhenius plots exhibit anomalies which conform with the above interpretation. The results obtained in dioxane and in toluene solutions are similar to earlier findings in methanol and n-hexane solutions respectively. This makes it possible to generalize the conclusions reached here to acrylic acid solutions in other solvents which may or may not associate with the monomer.     

Etude de la stabilisation du polychlorure de vinyle avec des molecules modeles—V. Stabilisation par l'α-phenyl-indole

α-Phenyl-indole is a secondary stabilizer of PVC; it reacts with labile allylic chlorine atoms by one or more substitutions, first on the hydrogen atom of the trisubstituted double bond in the heterocycle, and then on the aromatic rings. The reaction is catalysed by ZnCl₂ which is complexed with α-phenyl-indole. The substituted products are insensitive to HCl so that the stabilization is definite. α-Phenyl-indole may give synergistic effects with other stabilizers, but the condition is that they must be present in amounts enough to neutralize all the HCl produced.     

Action des sulfonyloxaziridines sur une imine. Obtention d'une nitrone par transfert regioselectif de l'oxygene sur l'azote

A pyrrolinic imine has been found to react concurrently with the nitrogen or the oxygen of a $\text{N}$-sulfonyl oxaziridine leading to a N-sulfonyl diaziridine and a nitrone respectively. By contrast an oxaziridine is obtained with a peracid. A possible relation between the regioselectivity of the oxygen transfer and the nature of the reagent is outlined.     

Decomposition d'hypobromites prepares par action de l'oxyde de mercure et du brome sur des alcools bicycliques pontes

Hydrobromites of bridged bicyclic alcohols have been decomposed to yield tetrahydrofuran-type ethers as well as fragmentation products. The latter results from the cleavage of the carbon-carbon bond α, β to the hydroxyl group. In the case of 3-hydroxy-3-methyl bicyclo[3.2.1]octane, conjugated ketones and brominated olefins are formed, whereas tetrahydrofuran-type ethers are formed only under different experimental conditions different from those applicable to general cases. The reaction mechanisms have been established. The influence of the various reaction parameters has been studied in order to obtain selectively either tetrahydrofuran-type ethers or a mixture of conjugated ketones and brominated olefins.