Mesure de la distribution des masses moléculaires entre ponts dans les réseaux

The classical theories of rubber elasticity allow a polymer network to be characterized by the mean molecular weight between crosslinks. This is measured by swelling or by determination of the elastic modulus. A method is described here that determines the distribution of the molecular weights between crosslinks, obtained by finding the spectrum of the freezing temperatures of a swelling solvent. It is known that the freezing point depends on the crystal size. It is proposed that the crystal size is equal to the distance between crosslinks in the swollen gel. The molecular weight between crosslinks and its distribution can be determined by the scaling laws.     

Étude de réactions à l'état solide entre l'arbre de Saturne et des sels contenant le groupement XO3

Résumé Le plomb utilisé sous forme d'arbre de Saturne possède une grande réactivité et permet de réduire les nitrates en nitrites. Il s'agit d'une réaction à l'état solide, débutant dès la température ordinaire. On a pu caractériser ainsi la présence de nitrites en mélangeant le plomb avec les nitrates de lithium, sodium, potassium, césium, cuivre, argent, magnésium, calcium, strontium, baryum, zinc, thallium, plomb, cobalt et nickel.

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Summary Lead used in the form of the lead tree has great reactivity and is able to reduce nitrates to nitrites. This involves a solid state reaction and starts at room temperature. In this way it is possible to detect the presence of nitrites after mixing the lead with the following nitrates — Li, Na, K, Cs, Cu, Ag, Mg, Ca, Sr, Ba, Zn, Tl, Pb, Co, Ni.

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Zusammenfassung In der Form des Bleibaumes ist Pb sehr reaktionsfähig und reduziert Nitrat zu Nitrit. Dabei handelt es sich um eine Festkörperreaktion, die bei gewöhnlicher Temperatur einsetzt. Nach Vermengen von Blei mit den Nitraten von Li, Na, K, Cs, Cu, Ag, Mg, Ca, Sr, Ba, Zn, Th, Pb, Co und Ni konnte die Anwesenheit von Nitrit festgestellt werden.

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En l'honneur du ProfesseurA. A. Benedetti-Pichler, pour son 70^e anniversaire.     

Emploi de la thermogravimétrie et de la spectrophotométrie infrarouge pour suivre les réactions à l'état solide

Résumé L'auteur indique sur des exemples variés comment on peut combiner les indications de la thermobalance et du spectromètre infrarouge pour suivre les réactions à l'état solide, qu'il se dégage ou non un produit gazeux: action de la strontiane sur les pyrophosphates, polymérisation spontanée des métaborates, adsorption du permanganate par le sulfate de baryum, combinaison supposée SiO₂ + 12 MoO₃, action de l'iode sur la magnésie. Ensuite, il étudie plus longuement la synthèse des chromites et la mise en solution par l'oxylithe des oxydes métalliques; cette dernière réaction s'effectue suivant quatre mécanismes différents illustrés par des exemples concrets.

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Summary The writer shows by means of varied examples how the information furnished by the thermobalance may be combined with that derived from the infra red spectrometer in following solid state reactions, which may or may not produce gaseous products. Examples are: action of strontium oxide on the pyrophosphates, spontaneous polymerization of metaborates, adsorption of permanganate by barium sulfate, alleged compound SiO₂ + 12 MoO₃, action of iodine on magnesia. The investigation also included a lengthy study of the synthesis of chromites and the solution of metal oxides by sodium peroxide. The latter reaction, effected by four different mechanisms, is illustrated by concrete examples.

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Zusammenfassung An Hand verschiedener Beispiele wird gezeigt, wie man mit Hilfe der Thermowaage und des IR-Spektrophotometers Festkörperreaktionen mit oder ohne Gasentwicklung verfolgen kann. Als solche Beispiele werden angeführt: die Einwirkung von Strontiumoxyd auf Pyrophosphat, die Spontanpolymerisation von Metaboraten, die Absorption von Permanganat durch Bariunisulfat, die Bildung des Gemisches SiO₂ + 12 MoO₃ durch Erhitzen von Oxin-Silicomolybdat, Einwirkung von Jod auf Magnesiumoxydhydrat. Weiters wird die Synthese von Chromiten und die Auflösung von Metalloxyden mit Natriumperoxyd ausfuhrlich erörtert. Der letztgenannte Vorgang verläuft nach vier verschiedenen Reaktionsmechanismen, die an konkreten Beispielen erklärt werden.

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Conférence prononcée le 25 avril 1961, au Congrès de chimie analytique de Budapest.     

Sur une réaction dans l'état solide entre le pentoxyde d'Antimoine et le mélange oxyde-nitrate de Fer-III

Résumé Dans la méthode préconisée parVortmann etMetzl pour le dosage de l'antimoine, l'addition d'oxyde ferrique au nitrate ferrique permet de réduire la quantité de ce dernier indispensable à l'oxydation quantitative de l'antimoine. Le produit de la réaction ne peut être un antimoniate véritable puisque son spectre d'absorption montre l'absence de bandes caractéristiques d'une telle substance. L'existence d'un oxyde double de fer et d'antimoine paraît donc plus probable, sa composition globale serait de la forme 1,4 Fe₂O₃ · Sb₂O₅. On montre également que des réactions analogues doivent exister quand on substitue au nitrate ferrique ceux de sodium, calcium, nickel et cobalt.

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Summary In the method recommended byVortmann andMetzl for the determination of antimony, the addition of ferric oxide to the ferric nitrate makes it possible to lower the quantity of the latter necessary for the quantitative oxidation of the antimony. The product of the reaction cannot be a real antimonate because its absorption spectrum shows the absence of the bands characteristic of such a substance. Therefore, the existence of a double oxide of iron and antimony seems more probable, its summary formula may be of the form: 1.4 Fe₂O₃ · Sb₂O₅. It has also been found that analogous reactions may occur when sodium, calcium, nickel, or cobalt nitrates are substituted for the ferric nitrate.

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Zusammenfassung Bei der vonVortmann undMetzl vorgeschlagenen Methode zur Bestimmung von Antimon kann man die zur quantitativen Oxydation des Antimons nötige Menge von Eisen(III)-nitrat durch Zugabe von Eisen(III)-oxyd herabsetzen. Das Reaktionsprodukt kann in Wahrheit kein Antimoniat sein, da sein Absorptionsspektrum die charakteristischen Banden dieser Substanz vermissen läßt. Die Existenz eines gemischten Eisen-Antimon-Oxyds scheint wahrscheinlicher, seine Zusammensetzung entspricht der Summenformel 1,4 Fe₂O₃ · Sb₂O₅. Es wurde gezeigt, daß analoge Reaktionen ablaufen, wenn an Stelle des Eisen(III)-nitrates die entsprechenden Salze des Natriums, des Calciums, des Nickels oder des Kobalts verwendet werden.

     

Etude des réactions de l'acétylformazyle et de ses dérivés avec les ions minéraux

Résumé L'étude systématique de l'acétylformazyle et de ses dérivés pour l'analyse à la touche à fourni des réactions sensibles permettant la recherche du mercure avec la thiosemicarbazone, du cuivre et du palladium avec l'oxime.

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Summary The systematic study of acetylformazyl and its derivatives for spot test analysis has yielded sensitive reactions which permit the detection of mercury by means of the thiosemicarbazone, and of copper and palladium with the oxime.

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Zusammenfassung Die systematische Untersuchung von Acetylformazyl und seinen Derivaten für die Zwecke der Tüpfelanalyse führte zu empfindlichen Reaktionen zur Prüfung auf Quecksilber mit dem Thiosemicarbazon, auf Kupfer und Palladium mit dem Oxim.

     

Forces de la répulsion dans la spectroscopie vibrationelle—II. L'influence combinée d'attraction et de répulsion entre les particules sur les profils des composantes isotropes des lignes vibrationelles à l'exemple des systèmes ioniques

Mutual effect of interparticle attraction and repulsion on isotropic Raman line contours and time correlation functions was studied. The theory of Burshtein et al. [Chem. Phys. Lett. 83, 335 (1981); 100, 155 (1983); Spectrochim. Acta 43A, 483 (1987)] was used, and broadening caused by repulsion forces was defined more precisely. The discussion of the results obtained was made with special reference to ionic systems (molten salts and salt glasses).     

Étude de la réactivité des radicaux α-ester : influence des centres stéréogènes en position α’ et β’

The formation of 2-syn and 2-anti addition products, between a 1-E olefin and an acyclic radical is under kinetic control, although addition of n-Bu₃Sn^• to the 1-Z leads to 1-E olefin. Hydride capture is often independent of the nature of the radical, but the difference of behaviour between A^• and B^• radicals results from their stability, induced by the existing chiral centres present in the molecule. Capture of the intermediate radical in α of the ester by deuterium occurs with a diastereomeric excess, varying between 30 and 78%, depending on the nature of the centres situated in α’ and β’ positions.     

Les réactions solvothermales : implications en recherche de base et dans les procédés industriels

Solvothermal reactions have been developed both in solid state chemistry and in material science. In a first approach, seven main domains can be defined for the applications of such reactions: (i) the synthesis of new materials, (ii) the development of new processes, (iii) the preparation of microcrystallites, (iv) the thin film deposition, (v) the sintering and (vi) the crystal growth at moderate temperature compared to the conventional processes, (vii) the waste-retreatment. These different domains involving either the basic research or the industrial applications, in particular in the area of ceramics, are presented and their potential developments are analysed.     

Transmission de l'effet de substituant a travers les systèmes insaturés—II. Relations entre les paramètres r.m.n. du 1H et du 13C des cyclohexène-2-ones-1 substituées en 3 et les constantes de réactivité

¹H and ¹³C n.m.r. spectra of 5,5-dimethyl cyclohex-2-en-1-ones substituted in position 3 have been analysed. Correlations of the chemical shifts of the ethylenic proton, the corresponding carbon and their coupling constant with Hammett type parameters provide a consistent picture of electronic effects transmitted through the unsaturated, non aromatic system. Systematic deviations shown for particular substituents reveal structural peculiarities and also effects that are not described by reactivity parameters.     

Réactivité des N1-tosylhydrazonates vis-à-vis du réactif de Lawesson,du cyanamide et des hydrazides : synthèse de thiadiazaphospholines et d’aminotriazoles tosylés

Reactivity of N¹-tosylhydrazonates towards Lawesson’s reagent, cyanamide and hydrazides: synthesis of tosylated thiadiazaphospholines and aminotriazoles. The reaction of N¹-tosylhydrazonates with the Lawesson reagent, cyanamide and hydrazides leads respectively to tosylated thiadiazaphospholines, C-aminotriazoles and N-aminotriazoles in good yields. The structure of all obtained products was determined on the basis of their IR and NMR data. To cite this article: M.B. Mosbah et al., C. R. Chimie 6 (2003).     

Mesure en laboratoire de la permittivité diélectrique moyenne fréquence de végétaux à 430 kHz à l'aide d'un capacimètre. Relation entre permittivité apparente d'un ensemble d'épis de blé et leur contenu en eau

The laboratory measurements presented here are additional measurements to those performed on a wheat crop by an electrostatic quadrupole at 430 kHz. They give a first calibration for the correlation between water content and apparent dielectric permittivity of ears. These measurements are performed by means of a capacimeter or a plane condenser of which the apparent permittivity is determined. Wheat ears are placed within the condenser and their permittivity is correlated to their water content. A theoretical approach (method of moments) presents the response of the condenser, containing ears similated to a 3D parallelepipedic body in an electromagnetic field.     

Utilisation des courbes de polarisation dans les dosages électrochimiques: Coulométrie á intensité constante

The conditions for coulometric determinations at constant intensity can be deduced from the polarisation curves; these are choice of current density and auxiliary systems, and possible accuracy of the determination. We have used for this study the results previously obtained for potentiometry at constant intensity.     

Dépôt de TiC sur fibres de carbone par CVD réactive: Influence des conditions expérimentales sur les caractéristiques des fibres obtenues

Uniform coating of the filament in a carbon yarn by titanium carbide occurs by direct reaction of titanium tetrachloride vapour and hydrogen with the surface of the fibre at temperatures exceeding 1200 K. Continuous fibre treatment is achieved under atmospheric pressure. Mechanical properties derived from tensile tests on single filaments permit the experimental CVD (chemical vapour deposition) conditions to be optimized. Temperature is the decisive factor: at 1240 K and for 0.8 min treatment, high quality C(TiC) fibres are obtained (σ_R = 2965MPa). At higher temperature the tensile strength decreases. In order to explain this phenomenon, variations in size of the carbon and the titanium carbide crystallites are studied with respect to experimental conditions.     

Influence de la cinétique des réactions chimiques sur les courbes de polarisation : Application à l'étude des complexes thiocyanés du titane(iv) et du titane(III)

The electrochemical oxidation-reduction of the system titanium(IV) — titanium(III) is slow at dropping mercury electrode in perchloric acid or hydrochloric acid, but becomes rapid in the presence of thiocyanate ions.On the basis of polarization curves, interpreted according to a preliminary theoretical study, the authors conclude that the rapid electrochemical reaction is the following: TiOH.SCN⁺² + H⁺ + e ? TiSCN⁺² + H₂OAn application of the findings to the polarographic determination of titanium is given.     

Réaction d’isomérisation de l’acide urocanique et de ses dérivés: stabilité comparée des isomères Z et E

Thermal and photochemical isomérisation of urocanic acid and its derivatives (O- and/or N-alkylated) have been studied. The data show the wavelength and the molar extinction coefficient-dependent photochemistry of E urocanic acid and its derivatives. Thermal isomérisation of these compounds is difficult and undergoes a “one-way” Z → E reaction. Thus, E isomers are thermodynamically more stable than the Z ones. Under basic conditions, derivatives having an unsubstitued imidazole ring (NH function free) exist in their anionic forms, which lowers the energy barrier without changing the isomérisation pathway.     

Réaction pseudo-multicomposants entre le glutaconate de diméthyle et des aldéhydes aromatiques induite par le bromure de phénylzinc : accès domino à des dihydropyranones 2,3,5-trisubstituées

Phenylzinc bromide enables a pseudo three-component reaction of methyl glutaconate and aromatic aldehydes. Unsaturated trisubstituted δ-valerolactones (dihydropyranones) are obtained in fair to good yields by an aldol/aldol/elimination/lactonization domino process that allows the formation of four new bonds in a single step. A putative reaction mechanism is proposed.     

Introduction a l'étude des sels basiques insolubles: Étude des courbes de précipitation des sels basiques insolubles. Produits de solubilité des sels basiques et des hydroxydes

A critical study of curves of precipitation of basic salts by alkali hydroxides shows that the irregularities observed on these curves do not always permit the deduction of the constitution of the salt. They indicate nevertheless the appearance of a new phase and this observation explains, in particular, the important number of wrongly defined basic salts which have been observed.The theory of the titre curves leads to the proposal of formulas permitting the calculation of solubility products of basic salts and even those of hydroxides which were determined very accurately by other methods.     

Transmission de l'effet de substituant à travers les systèmes insaturés-IV. Utilisation des relations de type Hammett avec les paramètres spectroscopiques i.r. et RMN pour la détermination des conformations de cétones α, β-éthyléniques aromatiques

The i.r. stretching frequencies of the carbonyl group and the chemical shift of the ethylenic proton in three series of α,β-unsaturated ketones, 3-substituted-5,5-dimethyl-2-cyclohexen-1-ones s-trans p-substituted-4-aryl-3-buten-2-ones and p-substituted-3-aryl-5,5-dimethyl-2-cyclo-hexen-1-ones, have been analysed using correlations with Hammett type substituent constants. The comparison of parameters ϱ of these correlations allows us to obtain quantitative information on the conformation of the last series of ketones. In this series, the dihedral angle between the aromatic ring and the plane of enonic system varies inversely with the resonance donor effect of substituent (0° for p-NH₂, 38° for NO₂).