Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. II. Influence de la variation de la sensibilite du calorimetre avec la temperature sur les valeurs trouvees pour les constantes de vitesse et les enthalpies de reaction

The variation with temperature of the sensitivity of a “Thermanalyse” microcalorimeter has been determined using the electrical calibration system of the apparatus. From the results, a method for the correction of the differential scanning microcalorimetric diagrams has been developed. The influence on the determination of the rate constants during kinetic studies of the decompositions of free radical initiators and on enthalpy measurements has been studied.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. VIII. Thermolyses de perbenzoates de t-butyle p-substitues. Discussions sur la correlation de hammett

The study of the thermolysis of some p-substituted t-butyl peroxybenzoates in diphenyl ether confirms that (i) electron-withdrawing groups stabilize the peroxydic bond, and (ii) electron-repelling groups make it weaker. However, as the influence of these substituents is not considerable, the differences between the kinetic or activation parameters being not much greater than experimental errors, one must observe some caution before drawing conclusions on the correlations between electronic effects and stability characteristic parameters.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. I. Considerations generales sur l''appareillage et les reactions de decomposition d''amorceurs radicalaires en solution

Kinetic parameters of decompositions of free-radical initiators can be determined by differential scanning microcalorimetry. A conduction microcalorimeter fitted with an inertia corrector can be used. A critical survey of the apparatus used and of the reactions studied has determined the working under which the measures must be carried out.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. VII. thermolyses de perbenzoates de t-butyle p-substitues. Influence des substituants

Kinetic studies performed by differential scanning microcalorimetry show that the stability of t-butyl p-substituted peroxybenzoates is slightly influenced by the electronic effects of substituents. No simple correlation is found between ln k_r and σ.     

Determinations cinetiques par microcalorimetrie differentielle programmation de temperature. IV. Parametres cinetiques del l'homolyse de l'azo-bis-isobutyronitrile en solution

Free-radical decomposition rate constants of A.I.B.N. in different solvents, obtained from differential scanning micro-calorimetry are analyzed; calculated kinetic parameters are discussed. Free energy of activation (ΔG^≠) is proposed as a characteristic of the thermal stability of free-radical initiators.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. IX. thermolyses de perbenzoates de t-butyle p-substitues. Parametres cinetiques et d'activation

Kinetic and activation parameters of thermolysis in several solvents are compared. The free activation enthalpy is taken as a specific characteristic of the thermal stability; it is then applied to “evaluate” the influence of aromatic ring substituents. A symbatic variation in the case of the activation energy and the pre-exponential factor of the Arrhenius relation as well as in that of the activation enthalpy and entropy are found. The significance of the corresponding kinetic compensation effect is discussed as well as that of the isokinetic temperature of the thermolysis of p-substituted peroxybenzoates.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. VI. Thermolyse d'azo-1,1′-(cyano-1 cyclanes) dans differents solvants

Bis-azo-cyanocyclo-pentane, -hexane and -heptane are prepared and the kinetics of their thermolysis in several solvents are studied by differential scanning microcalorimetry. Unlike activation enthalpy and entropy, activation free enthalpy does not depend on solvent. Moreover its variation with temperature is quite small in each kinetic study temperature range. Thus ΔG^# is given as an intrinsic stability characteristic of azo-nitriles. “Kinetic compensation effect” between ΔS^# and ΔH^# is discussed.     

Determinations cinetiques par analyse microcalorimetrique differentielle. XVI. Decomposition du percarbonate de O,O-t-butyle et O-isopropenyle en solution

Kinetic studies by differential scanning microcalorimetry have shown that the free radical decomposition of O,O-t-butyl and O-isopropenylperoxycarbonate is induced, to a great extent, by the addition of free radicals to the vinylic double bond. If the solvent can give stabilized free radicals, then acetonyl radicals add themselves to the double bond leading to acetonylacetone; in this case, the kinetic study allows the characteristic parameters of the thermal stability of the peroxycarbonate to be determined. When the radicals issued from the solvent can add themselves to the double bond, the induced decomposition finds expression in the acetonylation of the solvent; as for kinetics, such an enhancement of the reaction rate takes place that the “spontaneous” homolytic decomposition takes only a minor part even for very low concentrations of the peroxycarbonate solutions.     

Determinations cinetiques par analyse microcalorimetrique differentielle. XVII. Decomposition spontanee et induites du percarbonate de O,O-t-butyle et O-vinyle en solution

The mechanism of the free-radical decomposition of O,O-t-butyl and O-vinyl peroxycarbonate looks like that of the decomposition of the O,O-t-butyl and O-isopropenyl homolog. In such solvents as triisopropylbenzene, di-n-butyl phthalate or diphenyl oxide oxo-2-ethyl [HC(O)CH₂] and acetyl [CH₃C(O)^·] radicals add themselves to the peroxycarbonate double bond. This addition gives rise to an induced decomposition which is associated with the “spontaneous” thermolysis. In octadecane, the induced process originates in the addition of radicals produced from the solvent. As for its intrinsic thermal behaviour, O,O-t-butyl and O-vinyl peroxycarbonate ranks, before O,O-t-butyl and O-isopropenyl peroxycarbonate or t-butyl peroxybenzoate, among the most stable peroxyesters.     

Application de la thermogravimetrie,de l'analyse thermique differentielle et de la spectrographie d'absorption infrarouge a l'etude de la reaction entre l'oxyde de chrome(III) et les nitrates alcalins

Résumé On dose, à l'état solide, des mélanges chromate-bichromate de potassium, à côté d'oxyde de chrome(III), par spectrophotométrie d'absorption infrarouge et par analyse thermique différentielle. Certains aspects de la dissociation du bichromate de potassium ont été mis en évidence.

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Mixtures of chromate and dichromate were determined in the presence of chromium(III) by infrared spectroscopy and differential thermal analysis. Questions connected with the dissociation of potassium dichromate were also treated.

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Zusammenfassung Es wurde über die Bestimmung von Chromat-Bichromat Gemischen in fester Phase durch infrarote Spektroskopie und Differentialthermoanalyse in Gegenwart von Chrom(III) berichtet. Fragen der Dissoziation von Kaliumbichromat wurden ebenfalls erörtert.

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() (III). .

     

Determinations cinetiques par analyse microcalorimetrique differentielle. XV. Thermolyse de peroxydes de benzoyle p,p′-disubstitués en solution dans l'ether de diphenyle

Differential scanning microcalorimetric and chemical studies of the thermolysis of some p,p′-disubstituted benzoyl peroxides have been performed in diphenyl oxide as solvent. They have shown that the decomposition proceeds only via the homolysis of the peroxide bond; neither free radical induced nor autocatalytic processes occur. The activation parameters of the thermolysis of the peroxides have the same values as those found when propiophenone is used as solvent. Under these conditions, the free enthalpy of activation, ΔG^≠, is the intrinsic measure of the thermal stability of benzoyl peroxide and its p,p′-disubstituted derivatives.     

Etude du comportement thermique des n-alcanes dans des milieux hydrocarbones complexes par analyse calorimetrique differentielle. III. Etude en programmation discontinue de température

A study of the thermal behavior of n-alkanes in the solid state or in a hydrocarbon matrix has been carried out using a stepwise programming of temperature. In the case of pure n-alkanes the separation between the transition peak and the melting peak can be easily increased and the enthalpy of each thermal effect can be determined. The precipitated amount of n-alkanes contained in middle distillates has been obtained vs. temperature.     

Etude du fluorure de propargyle par RMN en phase nematique: Determination de la geometrie moleculaire et des signes des differentes constantes de couplage indirect

NMR spectra of proton, fluorine-19 and carbon-13 satellites of partially oriented propargyl fluoride have enabled the complete structure of this molecule to be determined. Agreement with microwave results is excellent, except for the carbon-fluorine bond length. Signs of all indirect coupling constants have been determined.     

Polymerisation du methacrylate de methyle par le chlorure de tertio-butylemagnesium en solution dans le tetrahydrofuranne—II Comportement de la polymerisation en fonction de la temperature et de la composition du magnesien

The polymerization of methylmethacrylate initiated by tert butyl-magnesium chloride in tetrahydrofuran has been studied in terms of yield and balance-sheet. It has been shown that only the symmetrical form of the Grignard reagent is efficient in initiating the polymerization. Initiation, propagation and termination mechanisms have been proposed.     

Tetrahydro anthraquinones disubstituees en - 1,5: etude de la regioselectivite de la reaction de diels-alder entre des naphtoquinones et des dienes attracteurs.

Diels-Alder reaction of - 2,4 pentadienoïc acid and its methyl ester (electron with-drawing) dienes with juglone and its derivatives is described. High regioselectivity is observed, the adducts have a “head-to-tail” geometry.     

Etude des transitions de phase du sulfate dibasique de plomb PbSO4, 2PbO: Influence de la vitesse de montee en temperature et de L'histoire thermique

Basic lead sulfate, PbSO₄·2PbO, was studied by means of DTA, X-ray diffraction and scanning electron microscopy. DTA runs at different heating rates showed that two kinds of thermal evolution are possible for PbSO₄·2PbO. IfT<40 deg h^–1, we have the normal process according to the following transitions: IfT>40 deg h^–1 the-PbSO₄·2PbO phase appears at 440 C, but is unstable and breaks down into monobasic and tetrabasic lead sulfates. Reaction enthalpies were evaluated and correlated with the cell volume variations determined by X-ray diffraction. An interpretation of the existence of two types of process is proposed.

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Zusammenfassung Basisches Bleisulfat PbSO₄·2PbO wurde mittels DTA, Röntgendiffraktometrie und Scanningelektronenmikroskopie untersucht. DTA-Versuche mit unterschiedlichen Aufheizgeschwindigkeiten haben gezeigt, da\ PbSO₄·2PbO auf zwei verschiedene Weisen thermisch gebildet werden kann. Bei¯T<40·h^–1 verlÄuft der normale Proze\ entsprechend den Reaktionsgleichungen Bei¯T>40 h^–1 tritt die-PbSO₄· 2PbO-Phase bei 440 C auf, ist jedoch instabil und zerfÄllt zu monobasischem und tetrabasischem Bleisulfat. Die Reaktionsenthalpien wurden bestimmt und mit den röntgendiffraktometrisch ermittelten VerÄnderungen des Elementarzellenvolumens in Beziehung gesetzt. Die Existenz von zwei Typen des Prozesses wird interpretiert.

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, - PbSO₄·2PbO. , , . 40 /. « » : 40/ 440 C PbSO₄·2PbO, , , . , - . .

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Nous remercions F. Chapuis et M. Andréani (Lab. Matériaux, E. C. F.) qui ont réalisés les clichés de microscopie.     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—III. Membranes non-ionisables contenant de la poly-n-vinylpyrrolidone

Equilibrium properties (swelling) and transport phenomena (dialysis) of non-ionizable membranes, obtained by radiation grafting of N-vinylpyrrolidone onto thin PTFE films, were studied. Grafting was conducted by the direct method with monomer solutions in benzene. The overall activation energy of grafting determined between 20 and 50° is high (12.5 kcal mol^?1): the reaction is controlled by the monomer diffusion into PTFE film. The length of grafted chains increases with temperature.The molality of the membranes decreases when the temperature of grafting increases; for a given grafting ratio, the swelling is higher for membranes containing a small number of long grafts than for membranes with numerous short branches. The transfer of both ions and water is a function of the free volume in the films, it depends on the grafting ratio and is not influenced by the preparation conditions.     

Etude du comportement thermique des n-alcanes dans des milieux hydrocarbones complexes par analyse calorimetrique differentielle. I. Etude du comportement thermique des n-alcanes en programmation lineaire de temperature

Middle distillates contain various amounts of n-alkanes which are responsible for low temperature properties. The thermal behavior of 14 alkanes ranging from n-C₁₂H₂₆ to C₂₅H₅₂ has been studied by means of a Mettler TA 2000 B heat flow DSC. Different hydrocarbon matrices such as gas oil (diesel) where n-alkanes have previously been removed, kerosene and gas oil containing a known distribution of n-alkanes have been used. A comparative study of the values of the enthalpy of dissolution obtained for each n-alkane in a gas oil with or without a distribution of n-alkanes has been carried out.     

Comparaison de la purification par fusion de zone et par cristallisation en colonne dans le cas d'amines aromatiques liquides a temperature ordinaire

Purification by zone melting of seven aromatic amines was studied; 400 g of substance could be purified at one time between +15° and -35°. Criteria of purity and some physical constants of puritied amines are given. A related method—column crystallisation-was also studied for the same starting materials and the results are compared. The two methods of purilication give comparable results. Column crystallisation does not give such good purification as zone melting, but has the advantages that it can be operated with continuous throughput, much less time is needed, and rather impure starting materials can be employed     

Reactions CO/H2 en phase liquide. Synthese de precurseurs de l'ethanol par homologation du methanol.: I. Influences de la temperature et de la pression

The CO/H₂ homologation of methanol to acetaldehyde and subsequently to its dimethyl acetal in the presence of cobalt acetate promoted by iodine was examined under various conditions. Temperature and pressure were found as critical parameters. High pressures (140 MPa) and low temperatures (160–170°C) give optimal yields and selectivity to acetaldehyde. According to pressure, temperature, contact time, gas ratio and ligand/catalyst ratio, the reaction is oriented towards acetaldehyde, its dimethyl acetal or methyl acetate.