Etude de la repartition de l'uranium dans les roches par la methode des traces de fission. Application a l'echantillonage en vue du dosage de l'uranium

The distribution of uranium in two different rock species: basalt from the Fangataufa atoll (located in Polynesia) and granit from the Hoggar mountains (located in Sahara) was studied by the fission track method. The two distributions observed appear quite different: uranium is uniformly distributed in the vitrous part of the basalt while in granit it is located on the intergranular joints. Applying the sampling model proposed by A. D. WILSON to the observed distributions of uranium, the weight of the analytical sample corresponding to a required sampling error can be estimated. Results show that representative sample weights of the bulk powdered material, as usually obtained by milling, are about some tenths of milligrams for basalt and more than the grams for granit (for uranium analysis). So, in trace element analysis, the sampling error could be more important than the analytical one. This fact could explain the relatively poor accuracy of trace determinations in rock samples (including the reference samples).      

Etude de la séparation de traces de mercure ionique par adsorption,en milieu aqueux,sur verre sodocalcique. Application à la séparation Hg2+-organomercuriels

The separation conditions of traces of ionic mercury from aqueous solution on microbeads of soda lime are studied theoretically and established experimentally. The formation of a stable complex of the ion with ethylene diamine allows to operate at pH 7–8. The efficiency of the exchange is close to 96%. The methods allows the separation and essay of ionic mercury in presence of various organomercuric compounds.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction de L'acide nitrique par les oxydes de tri-n-hexylphosphine,de tri-cyclohexylphosphine et de tri-n-octylphosphine

The distribution of nitric acid between an aqueous phase and a solution of THPO, TcHPO and TOPO in benzene was measured at 25°. The apparent stability constants K₁' were found to be 17.2±1.0 (M)^-2 for THPO.HNO₃, 7.0±0.8 (M)^-2 for TcHPO.HNO₃ and 15.2 ± I.I (M)^-2 for TOPO.HNO3. The stoichionetry of the last complex was confirmed in n-octane solution at constant ionic strength in the aqueous phase.     

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.     

Sels d'atdp—20 : Relations reactivite-structure dans les cinetiques de decomposition de sels d'atdp substitues. hypersensibilite a des substituants en position 3 de la

The kinetics of decomposition of various propyloxy phosphonium chlorides, the chain of which is substituted with non polar groups in position 2 and polar groups in position 3, have been measured in pyridine and in DMF. The validity of Taft correlation with σ^* parameters have been ascertained within each of the three linear, branched and neopentylic series, using Exner's criterion. In both solvents, it appeared that the sensitivity parameter ?^* for the neopentylic series varies considerably with the temperature and may reach unusually high values. This phenomenon is interpreted by a proximity effect between the substituent and the seat of the reaction, due to steric constraints.     

Action des halogenures d'alkylmagnesium sur les pyrones-2—VI : Etude de la regioselectivite de l'ion enolate intermediaire de la reaction

Grignard reagents normally react with 2H-pyrones to yield unsaturated ketols, dihydropyranols, dienones and 2H-pyrans. In some cases, products are obtained by attack on the most sterically crowded position of the enolate ion. Since steric hindrance is an unsatisfactory basis for predicting the reactivity, we have applied a theoretical study to this problem. The model used is based on an enlarged electronic delocalization in the transition state, and allows the interpretation of the regioselectivity of the reaction.     

Dependance conformationnelle de l'effet isotopique dans les reactions d'addition nucleophiles : Influence du sens d'attaque sur la variation du terme hyperconjugatif

The secondary kinetic deuterium isotope effects measured in addition reactions of sulfite and borohydride ions has confirmed the importance of the hyperconjugative factor. Semi-quantitative evaluation of this stabilizing factor by calculating the orbital overlap evolution during reaction shows that the hyperconjugative contribution to the isotope effect is much more important during equatorial attack than during axial attack. This explains why isotope effects are similar for the additions, though their directions of attack are opposite and their transition states located differently along the reaction coordinate.     

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.     

L'addition des organomagnesiens aliphatiques satures sur les triples liaisons disubstituees non conjuguees: IV. Influence d'un groupement fonctionnel thioether en α de la triple liaison. Action catalytique du cuivre

The addition reaction of ethylmagnesium bromide to the triple bond of the compounds of general formula EtSCH₂CCCH₂Y (where Y is the basic group OH, OR, NR₂, or SEt) is very weakly activated by the thioether group. Catalysis by magnesium impurities may be involved.With 1-ethylthio-4-dialkylamino-2-butynes (Y NR₂), (E) trisubstituted ethylenic compounds are selectively obtained. The reaction more readily occurs after the addition of cuprous chloride to the Grignard solution, and then its stereoselecitvity may be reversed.     

Stereochimie de la des benzoates d'argent sur des diesters iododesoxy ns: I- Action des benzoates d'argent sur des di-o-aroyl-1,2 iododesoxy-3 ns-glycerols

The stereochemistry of the reaction of silver benzoates on chiral di-O-aroyl-1,2 iododeoxy-3-sn-glycerols has been reinvestigated. The reaction proceeds either with or without neighbouring group participation, depending on : - possible electrophilic assistance by the silver ion to the ionisation of the substrate (occuring only with dissociated silver salts), - ability of substituants R¹ and R² on the substrates to stabilize a positive charge. Rearrangements are at minimum with R¹ and R² electronreleasing groups in the substrate, silver salts un-or weakly dissociated and bearing a good nucleophile. For one case, a regio- and stereo specific reaction is observed.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction del'acide nitrique par quelques dioxydes de diphosphine

The distribution of nitric acid between an aqueous phase of constant or variable ionic strength and a benzene solution of diphosphine dioxide can be explained by the following reactions H⁺_a+ NO_3^-a+ DiPO₀ ? D1PO·HNO₃₀ H⁺_a+ NO_3^-a+ DiPO·HNO₃₀ ? DiPO·2 HNO₃₀ At constant ionic strength, the stability constants K₁″ were determined for the complexes 1,1-DiPO·HNO₃ (98 ± 01 (M)^-1), 1,4-DiPO·HNO₃(44±3 (M)_-1) and 1,5-DiPO·HNO₃ (51 ± 1 (M)^-1). The constants K₁₁″ for the complexes 1,1-DiPO·2 HNO₃ and 1,5-DiPO.2 HNO₃ are respectively 035±001 (M)^-1 and 62 ±0.05 (M)^-1 at 25°. With an aqueous phase of variable ionic strength, values of K₁'=54±7 (M)^-2 for 1,5-D1PO.HNO₃ and K_II'=65 ± 04 (M)^-2 for 1,5-DiPO·2 HN0₃ were obtained     

Action des halogenures d'alkylmagnesium sur les pyrones-2—V : Action de l'iodure de methylmagnesium sur des alkylpyrones-2 non substituees en position 4

To check if only 4-substituted 2-pyrones lead to 2H-pyrans with Grignard reagents, the reactions of 4-unsubstituted 2-pyrones with methylmagnesium iodide have been studied. From 3, 5, 6 trisubstituted 2-pyrones, 2H-pyrans may be obtained; but 5,6-disubstituted 2-pyrones give only linear products.     

Effets de la nature de substituants sur les constantes d'acidité et les constantes de stabilité des complexes de quelques acides nitroso-5-barbituriques

The effects of substituents on the acidity constants and stability constants of complexes of some 5-nitrosobarbituric acids). The acidity constants of some 5-nitrosobarbituric acids (violuric acids) vary according to the degree of substitution and the nature of the substituent at the 1- and 3-positions of the pyrimidine ring. The value obtained at ionic strength 0.5 mol l^?1 made it possible to calculate the stability constants of simple complexes of divalent cations (Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Fe²⁺). Potentiometric titrations were applied.     

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.     

Formation d'enolates cetoniques par action d'organomagnesiens mixtes dans l'hexamethylphosphorotriamide sur des esters. : Direction des enolisations,limites, utilisation a la preparation de cetones

Alkylmagnesium halides in HMPA react with aliphatic esters to form predominantly the less substituted ketonic enolates. The direction of these enolizations is more selective than that of intermediate ketones. Aliphatic esters are only slightly or not at all enolized under these conditions. Hydrolysis, deuterolysis and alkylation of the ketonic enolates give the corresponding ketones. Benzoic acid derivatives and α-β unsaturated aliphatic and aromatic esters give only low yields of ketonic enolates. The low enolization of the intermediate ketones by these alkylmagnesium halides can explain this result.     

Reactivite chimique et photochimique dans les milieux micellaires et les microemulsions—III : Mise en evidence de l'importance des processus interfaciaux sur une reaction de photoisomerisation

The E ? Z photoisomerization of the O-methyl ether of the oxime of 2-acetylnaphthalene has been studied in various microemulsions. The results obtained with variations of surfactant concentrations or with addition of sodium chloride show the importance of interfacial processes in colloïdal systems.     

Insertion de so2 dans la liaison titane—carbone: I. Diastereotopie et diastereoisomerie engendrees par la presence d'un atome de soufre chiral dans les produits d'insertion

Sulfur dioxide insertion reactions in titanium—carbon bonds are studied with two types of titanocene complexes: Cp₂Ti(C₆F₅)R and CpCp′Ti(C₆F₅)R. The NMR spectra of the insertion products from the first type of complex are typical for O-sulfinated complexes having a chiral sulfur atom. Starting from the second type or complex two diastereoisomers have been detected (diastereoisomery Ti, S).