Sur le Polymorphisme du barbital et le systeme eau-barbital

The crystal structures of three forms (I, II and IV) of barbital are well known.The DTA curve of barbital I is marked by only one endotherm, at 186°, which is the melting point of this crystalline form. For barbital II, the DTA curve shows a first endotherm at 160°, which indicates the transition point II I, and then an endotherm at 186° for the melting of form I. By fast cooling of a boiling saturated aqueous solution, another crystalline form of barbital (form X) can be obtained. The DTA curve of this new sample shows another endotherm, at 119°, preceding the endotherms at 160 and 186°. Though the TG curve does not indicate any weight loss at this temperature, this endotherm does not indicate a new phase transition, but a monotectic equilibrium.This monotectic equilibrium (x _L1=78 mol % H₂O,x _L2=98 mol % H₂O) is observed at 119° in the phase diagrams (isochöric sections atV/m=7 cm³·g^–1) of the water-barbital systems established for form I, form II and form X.

---

Zusammenfassung Die Kristallstrukturen von 3 Barbitalformen (I, II und IV) sind gut bekannt. Die DTA-Kurve von Barbital I weist nur einen endothermen Peak bei 186° auf, der dem Schmelzpunkt dieser kristallinen Form entspricht. Die DTA-Kurve von Barbital II zeigt einen ersten endothermen, dem Umwandlungspunkt II I kennzeichnenden Peak bei 160° und dann einen zweiten endothermen Peak bei 186° für das Schmelzen der Form I. Durch schnelles Abkühlen einer kochenden gesättigten wässrigen Lösung kann eine andere kristalline Form des Barbitais (Form X) erhalten werden. Die DTA-Kurve dieser neuen Probe zeigt einen weiteren endothermen Peak bei 119°. Obwohl aus der TG-Kurve bei dieser Temperatur kein Gewichtsverlust ersichtlich ist, zeigt dieser endotherme Peak doch keinen neuen Phasenübergang, sondern ein monotektisches Gleichgewicht an. Dieses monotektische Gleichgewicht (x _L1=78 mol% H₂O,x _L2=98 mol% H₂O) wird in den Phasendiagrammen (isochore Schnittpunkte beiV/m=7 cm³·g^–1) der für die Formen I, II and X aufgestellten Wasser/Barbital-Systeme bei 119° beobachtet.

---

: I, II IV. I 186°, . II 160°, II I, 186°, I. ( X), . 119°, 160 186°. - , , . (x _Li=78 % ,x _Li=98 % ) 119° ( V/m=7 cm³ · ^–1) - , I, II X.

---

---

A la suite de ce travail, nous envisageons également de rechercher les phases qui seraient susceptibles d'abaisser la température de l'équilibre monotectique.     

Relations entre le second coefficient du viriel A2 et la masse moleculaire,dans le systeme polystyrene-benzene

We present results obtained by osmometry on the polystyrene-benzene system at 24°C as a function of the polymer molecular weight. The variation of the second virial coefficient, as predicted by the Flory-Krigbaum theory of dilute solutions is lower than that obtained by our osmotic measurements: this difference is discussed. Using the Kurata method, we determined the unperturbed dimensions of the macromolecule. Lastly, we established the equation for the variation of the mean square distance with molecular weight for the polystyrene-benzene system.     

Formation de radicaux libres dans des substitutions nucleophiles: Polymerisation du styrene par le systeme: thiolate de sodium-halogenure benzylique

The reaction between sodium thiolates and benzylic halides gives rise to free radicals, some of which are benzylic radicals characterized by ESR spectroscopy using the spin-trapping technique. Furthermore the studied reaction is able to initiate the radical polymerization of styrene. A model which rationalizes the experimental results is proposed.     

Influence des traitements thermiques sur l'etablissement des equilibres dans le systeme binaire hydroxyde de lithium-hydroxyde de sodium

Résumé L'utilisation systématique de recuits, contrôlés par des examens radiocristallographiques à températures variables, a permis de faire disparaître les équilibres métastables qui se manifestent entre les hydroxydes de lithium et de sodium. Trois composés sont identifiés avec certitude: 2 LiOH · NaOH, LiOH · NaOH et LiOH · 2 NaOH. Le composé équimolaire est dimorphe, la variété haute température étant de symétrie cubique.

---

The systematic use of annealing operations controlled by radiocrystallographic examinations at various temperatures permits the elimination of metastable equilibria which occur between lithium and sodium hydroxydes. Three compounds have been characterized with certainty 2 LiOH · NaOH, LiOH · NaOH and LiOH · 2 NaOH. The equimolar compound presents in two crystalline forms: the high-temperature variety crystallizes in the cubic system.

---

Zusammenfassung Die systematische Anwendung von Prozessen der Wärmebehandlung, welche durch radiokristallographische Untersuchungen bei verschiedenen Temperaturen kontrolliert wurde, ermöglicht den Abbruch der zwischen dem Lithium- und Natriumhydroxid bestehenden metastabilen Gleichgewichte. Drei Verbindungen konnten mit Sicherheit charakterisiert werden: 2 LiOH · NaOH, LiOH · NaOH und LiOH · 2 NaOH. Die äquimolare Verbindung ist dimorph, wobei die bei höherer Temperatur stabile Art eine kubische Symmetrie besitzt.

---

, , , . :2LiOH. NaOH, LiOH. NaOH LiOH. 2 NaOH. , .

     

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.     

Etude calorimetrique des enthalpies de dilution de NH3 dans le systeme binaire HF-NH3

Enthalpies of dilution of NH₃ in the binary system HF-NH₃ have been determined using a suitable home-made calorimeter. Compilation of the results gives the enthalpy of reaction of gaseous NH₃ with a HF-NH₃ solution, in the NH₃ low concentration region (x_NH3 < 14,6 %).     

Mise en évidence d'une solution solide de type spinelle dans le diagramme de phase du systeme InS

Evidence is presented for normal-spinel domain of homogeneity between the compositions InS_1.50?ε and InS_1.35. Structural study of a single crystal of composition InS_1.44 indicates indium vacancies on the tetrahedral sites. The compound In₂S₃, regardless of conditions of formation, is a tetragonal superstructure of the spinel lattice (a₀) with $\text{a = a}{}_0\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and c = 3a₀. The spinel-type domain shows peritectic decomposition at 850°C for the composition InS_1.40.     

Etude par spectroscopie d'emission optique de decharges radiofrequence et micro-onde lors du depot chimique en phase vapeur (PACVD) dans le systeme Si-C-H-Ar

This work highlights optical emission spectroscopy (OES) results used for a better understanding of processes occuring in radiofrequency and microwave plasma enhanced chemical vapor deposition in the Si-C-H-Ar gas system. Optical lines such as Si⁺ and H_α (λ = 634.71; 656.29 nm), C₂ (λ = 516.52 nm), CH and SiH (λ = 431.42; 412.80 nm) can be considered as tracers of chemical species in the plasmas. Process parameters (growth rate, composition, residual stresses in the films and gas temperature) have their optical signatures (respectively: Si⁺, H_α lines and rotational G¹Σ⁺g → B¹Σ⁺u structure of H₂).     

Stereochime de reactions au niveau des liaisons silicium (ou germanium)— phosphore dans le systeme dimethyl-1,2 sila (ou germa)) cyclopentanique

The stereochemistry of nucleophilic displacement of diethylphosphino leaving group from geometrical isomers of 1,2-dimethy -1-diethylphosphino-1-sila (or germa) cyclopentane 1 (or 2 has been studied. Retention of configuration at Si (or Ge) atom was found in reduction with LiAlH₄(Et₂OorTHF), and inversion with bdLiBH₄. With reagents like n-butyllithium, allyllithium or allylmagnesium bromide, 1 (or 2) gives retention of configuration. Alcohols and acidic reagents react far more rapidly, but reactions are not (or weakly) stereospecific. PR₂; is a poor leaving group, neighbouring hydrogen atom in the Sommer-Corriu's scale.The stereochemistry of addition reactions of 1 (or 2) with various unsaturated derivatives (carbonyl and dissymetric ethylenic derivatives, ambident nucleophiles) has been also investigated. It was shown that these reactions are both regiospecitic and stercospecific, and proceed with retention at the silicon (or germanium) centre.The stereochemical results are consistent with recent conclusions that S_N-Si retention reactions involve frontier orbital interactions.Relative configurations of these geometrical isomers, and the stereochemistry of their reactions, were assigned by pmr and cmr spectroscopy.     

Permeabilite selective et solvatation preferentielle

Experimental data concerning the preferential solvation displayed by polyvinylpyrrolidone (PVP) dissolved in various mixed solvents are compared with the selectivity observed when a membrane, prepared by grafting vinylpyrrolidone into a thin film of polytetrafluoroethylene, is used to fractionate the same binary liquid mixtures by pervaporation. The investigation systems are:—ethanol/1,2- dichloroethane, ethanol/chloroform and acetic acid/1,2- dichloroethane. A close correlation is found between the two phenomena. The component which, in solution, is preferentially sorbed by polyvinylpyrrolidone, diffuses more readily through the PTFE-PVP membrane. When an inversion occurs, at a given concentration, in the preferential solvation, an inversion of selectivity is also observed in pervaporation at the same feed liquid composition.     

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.     

Une micro-reaction pour le manganese dans les minerais et dans les silicates

A rapid and sensitive method is described for the detection of manganese in rocks, silicates, ores and minerals. The reagent is a 5 % alcoholic solution of 8-hydroxyquinoline. A drop of the solution to be tested suffices for the test. Other elements present in the substance under examination do not interfere. The method can be used for field tests.     

Changements de phase dans le benzenesulfonate de baryum

Résumé Le comportement thermique du benzènesulfonate de baryum a été étudié par TG et ATD. Au premier chauffage, ce sel subit deux transitions à 340 et 400 C. Au cours des chauffages successifs, si la seconde transformation est réversible, le premier pic endothermique disparaÎt progressivement tandis que simultanément un nouveau pic apparaÎt à 320 C. Une nouvelle phase a été identifiée par Rayons X, à température ambiante. Les chaleurs de transition ont été calculées.

---

The thermal behaviour of barium benzenesulphonate has been studied by TG and DTA.On first heating, this salt undergoes two transitions at 340 and 400.During successive heatings, if the second transformation is reversible, the first endothermal peak gradually disappears and in the same time a new one takes place at 320.A new phase was identified by X-ray analysis, at room temperature.The heats of transition were calculated.

---

Zusammenfassung Das thermische Verhalten von Bariumbenzolsulphonat wurde durch TG und DTA untersucht. Beim ersten Aufheizen erfÄhrt dieses Salz zwei übergÄnge bei 340 und 400. WÄhrend aufeinanderfolgenden Aufheizungen verschwindet bei reversibeler zweiter Umwandlung der erste endotherme Peak allmÄhlich und gleichzeitig erscheint ein neuer bei 320. Eine neue Phase wurde durch Röntgenanalyse bei Zimmertemperatur identifiziert. Die übergangswÄrmen wurden berechnet.

---

. 340 400. , , , 320. . .

     

Effets rotationnels dans le cisaillement d'un milieu granulaire

A 2D granular medium composed of disks with elastic interactions is described macroscopically as a micropolar elastic medium. When it is sheared between two rigid walls, this theory predicts a localization of grain rotation gradients near the walls. If one introduces friction between disks above a critical strain, another solution appears with localized shear band formation in the bulk of the material. The existence of this solution requires however a decrease of the effective friction coefficient when the grains begin to flow and a non-zero resistance to rolling.     

Metallation des halogenures d'aryle par le tributylstannyllithium dans le tetrahydrofuranne

The metallation of aryl halides with tributylstannyllithium in THF proceeds via at least three different mechanisms whose relative rates depend on the nature of the halogen, the substrate and the experimental conditions. In the case of aryl bromides, a halogenmetal exchange (major process) is competing with a radical mechanism. With aryl chlorides, an arynic process, a halogenmetal exchange and a radical mechanism are involved. Finally, with aryl fluorides, the arynic process is usual, but it may be strongly competed by a radical mechanism whenever suitable experimental conditions are arranged.     

Photocatalyse appliquee a la metathese dans le cas du systeme W(CO)6/CCl4/hv. Proprietes des precurseurs et role du solvant

Catalysts which are active in the olefin metathesis reaction are formed by irradiation of W(CO)₆ in CCl₄. It is shown that the catalysis is of heterogeneous nature, although the involvement of soluble species cannot be excluded. CCl₄ reacts during the irradiation but has no specific influence on the thermal metathesis reaction. It is also shown that various precursors exist, depending on the irradiation time. Carbonyl-containing compounds yield catalysts which are highly active, but which have short lifetimes. On the other hand, the more condensed compounds, in which there are practically no carbonyl groups, which correspond to long irradiation times, yield species of relatively low activity, but with longer lifetimes. This effect is attributed to a change of the ligand field at the reaction centre.     

Etude sur le dosage du carbone total dans le monocarbure d'uranium

A comparative study is made of the reproducibilities obtained for the determination of total carbon in uranium monocarbide by different analytical techniques: macro and microgravimetry, electrical conductivity, thermal conductivity, coulometry, gaseous volumetry and manometry.