Etude de la decomposition thermique des polyheteroarylenes

An investigation was made of the thermal and thermooxidative decompositions of polybenzimidazopyrrolones and polybenzimidazobenzoquinolines, as well as a number of heterocyclic compounds modelling the linkages and individual fragments of these polymers. It was established that in the pyrolyses of the polyheteroarylenes and the corresponding model compounds the destruction of cycles occurs either simultaneously with cleveage of the C_ar-H bond or at a higher temperature. It was shown that the completely aromatic compounds and the heterocyclic compounds condensed with the benzene nucleus are the most thermostable of the investigated compounds. A comparative study revealed a correlation between the structures and thermal stabilities of the studied compounds.

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Zusammenfassung Die thermische und thermooxydative Zersetzung von Polybenzimidazopyrrolonen und Polybenzimidazobenzochinolinen und einige der die Bindungen und individuellen Fragmente modellierenden heterozyklischen Verbindungen dieser Polymere wurden untersucht. Es wurde festgestellt, daß bei der Pyrolyse von Polyheteroarylenen und der entsprechenden Modellverbindungen das Aufsprengen der Ringe entweder gleichzeitig mit der Spaltung der C_ar-H-Bindung oder bei höheren Temperaturen erfolgt. Von den untersuchten Verbindungen sind die vollständig aromatischen und die mit Benzolringen kondensierten heterozyklischen Verbindungen am thermostabilsten. Eine vergleichende Untersuchung der Struktur und Thermostabilität der untersuchten Verbindungen ergab eine Korrelation.

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Etude de la stabilite thermique des ethylates alcalins

Résumé La décomposition thermique des éthylates de Li, Na, K, Rb, Cs et de leurs solvates a été étudiée par thermogravimétrie couplée à un dispositif de microsublimation et par analyse thermique différentielle. La réaction de décomposition thermique des éthylates alcalins est complexe et conduit à la formation simultanée d'hydrogène et d'éthylène; les résidus de décomposition ne correspondent à aucun composé défini.

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The thermal dissociation of Li, Na, K, Rb and Cs alcoholates and their respective solvates has been studied by DTA and TG coupled with a gas analysis device. The reaction of decomposition is complex, and hydrogen and ethylene are evolved. The solid residue is a mixture of several compounds.

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Zusammenfassung Die thermische Zersetzung der Äthylate von Li, Na, K, Rb, Cs und ihrer Solvate wurde durch thermogravimetrische Analyse mit einer Mikrosublimierungsvorrichtung gekoppelt, sowie mit der Differentialthermoanalyse untersucht. Die thermische Zersetzungsreaktion der alkalischen Äthylate ist komplex und führt zur simultanen Bildung von Wasserstoff und Äthylen; die Zersetzungsrückstände entsprechen keiner definierten Verbindung.

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Nous tenons à remercier la Société ELF-ERAP à Solaize (Rhône) et plus particulièrement Monsieur Finas qui ont eu l'amabilité de nous fournir un mélange étalon de différents hydrocarbures gazeux.     

Etude theorique (cndo/s) des etats excites et des transitions electroniques de 2h-chromenes representant la partie responsable de l'ouverture photochimique de spiropyrannes

The excited states and electronic transitions of some 2H-chromenes (considered responsible for photochemical opening of photochromic spiropyrans) have been studied. The relative positions of nπ^* and ππ^* singlet and triplet energy levels of these compounds allow a satisfactory interpretation of their optical properties. Also highly localized electronic charge transfers are demonstrated in the case of 2H-chromenes substituted by a nitro group.     

Etude theorique de la premiere protonation de la proflavine

A comparison between theory and experiment (the last performed by J. H. Lhoste) gives consitent results pertaining to the difference in acid-base behaviour of proflavin in the ground state and in the excited singlet and triplet states. In particular, several facts emerge. An extraordinary inequality between the different pK′s of acid-base equilibria are indicated: p_triplet^K < p_fondamental^K < p_singulet^K A change occured by protonation in the electronic configuration of the lowest triplet state of that molecule and the variation of solvation energy during the absorption ground state-first excited singlet state plays an important part.     

Etude de la degradation thermique des oligomeres du polyacrylonitrile

To obtain more information on the reactions during the pyrolysis of polyacrylonitrile at 290° in air, we studied the thermal degradation of its trimers, tetramers and pentamers having the general formula: R  CH(CN)  CH₂  CH(CN)_n?1  R where R = H or CH₃ and n = 3,4,5. Study by gas chromatography of the volatile compounds produced during pyrolysis at 290° and 770° showed that the first step of the degradation is homolytic scission of the chain. There are then intra and intermolecular polymerisations of the nitrile groups and formation of a ladder polymer. This reaction is clearly exothermic only for pentamers. This increase of the reactivity with DP is borne out by a kinetic study by EPR of the pyrolysis in air at 290°, oxidation of the ladder polymer giving a paramagnetic solid. Its EPR characteristics (band width and number of spins per g) are very dependent of the DP and nature of the end-groups, H or CH₃, of the pyrolysed oligomer.     

Etude thermique de la N-methylmorpholine N-oxyde et de sa complexation avec l'eau

Résumé La N-méthylmorpholine N-oxyde (MMNO) a une température de fusion de 184.2°, une enthalpie de fusion de 160.5 J/g et une chaleur de décomposition de 1340 J/g. Son hydratation a été étudiée par analyse calorimétrique différentielle et par gravimétrie. A l'air et à la température ambiante, la quantité totale d'eau qui a diffusé dans la MMNO correspond à quatre molécules d'eau par molécule de MMNO. Plusieurs complexes MMNO-H₂O cristallins ont été mis en évidence par analyse calorimétrique differentielle: un complexe MMNO-2.5 H₂O (T _f =40.5°,H _f =143.4 J/g), un complexe MMNO-1 H₂O (T _f = 75.6°,H _f =160.5 J/g) et un complexe dont la quantité d'eau n'a pas été déterminée (T _f =102°,H _f =95 J/g).

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N-methylmorpholine N-oxide (MMNO) has a melting temperature of 184.2°, an enthalpy of fusion of 160.5 J/g and a heat of decomposition of 1340 J/g. Its hydration has been investigated by differential scanning calorimetry (DSC) and by gravimetry.In air and at room temperature, the total amount of water diffusing into MMNO corresponds to four molecules of H₂O per molecule of MMNO.Several MMNO-H₂O crystalline complexes have been studied by DSC: an MMNO-2.5 H₂O complex (T _f =40.5°,H _f =143.4 J/g), an MMNO-1 H₂O complex (T _f =75.6°,H _f =160.5 J/g) and a complex with an unknown amount of water (T _f =102°,H _f =95 J/g).

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Zusammenfassung Das N-Methylmorpholin N-Oxid (MMNO) hat eine Schmelztemperatur von 184.2°, eine Schmelzenthalpie von 160.5 J/g und eine Zersetzungswärme von 1340 J/g. Seine Hydratisierung wurde durch differentialkalorimetrische Analyse und durch Thermogravimetrie untersucht.In Luft und bei Raumtemperatur entspricht die gesamte, in das MMNO diffundierte Wassermenge 4 Wassermoleküle pro Molekül MMNO.Durch die differentialkalorimetrische Analyse wurden verschiedene kristalline MMNO-H₂O-Komplexe nachgewiesen: ein Komplex MMNO-2.5 H₂O (T _f =40.5°,H _f =143.4 J/g), ein Komplex MMNO-1 H₂O (T _f =75.6°,H _f =160.5 J/g) und ein Komplex, dessen Wassergehalt nicht bestimmt wurde (T _f =102°,H _f =95 J/g).

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N- -N- (MMNO) 184.2°, - 160.5 /, -1340 /. () MMNO. , MMNO , MMNO. MMNO ₂: MMNO · 2.5 ₂, _f =40.5°,H _f =143.4 /, MMNO · 1₂-T _f = 75.6°,H _f = 160.5 / , _f =102°,H _f =95 /.

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Nous tenons à remercier Monsieur H. Chanzy, Maître de Recherche au Centre de Recherches sur les Macromolécules Végétales (Grenoble), et son équipe de leur aide et de leurs conseils pour la préparation des produits.     

Etude thermodynamique de la decomposition thermique des hydrates du chlorure de magnesium

The thermodynamic study of the different compounds of the system MgCl₂, H₂O, HCl allows to draw the stability diagram of the 8 solid phases into a three-dimensional space (temperature, total pressure and ratio of HCl and H₂O partial pressures). The evolution of the composition of solid and gaseous phases during an isobaric heating is described. The conclusions of this study are in good agreement with the experimental results obtained in laboratory and with the industrial requirements set for the different steps of the dehydration of MgCl₂.     

Etude thermodynamique de la décomposition thermique des hydroxynitrates de zinc

The reaction scheme of thermal decomposition for four zinc hydroxynitrates was investigated by means of differential scanning calorimetry, thermogravimetry, mass spectrometry, and radiocrystallography. The thermal transformation of Zn(OH)(NO₃) · H₂O and of Zn₃(OH)₄(NO₃)₂ involves the formation of gaseous water and nitric acid from an actual chemical reaction. This reaction is not observed for Zn₅(OH)₈(NO₃)₂ · 2H₂O and Zn₅(OH)₈(NO₃)₂. These results show that the formation of gaseous nitric acid molecules inside the solids is specific to hydroxynitrates of divalent metals M, whose lamellar crystalline structure is characterized by a stacking of hexagonal close-packed layers of formula MX_2+m, where m = 0 or 1 and X = OH^?, H₂O, or NO^?₃.     

Etude de la decomposition thermique de fluorapatites carbonatees

Using a precipitation method, variably carbonated samples of fluorapatite-like francolite were prepared from solutions containing diammonium phosphate, ammonium fluoride and ammonium carbonate. Thermal analysis, gas chromatography and IR spectroscopy were performed. The results show that cyanate ions (CNO^?) appear between 400 and 500 °C, probably as a result of the thermal evolution of ammonium ions. Above 500°C, nitrogen gas was detected with CO₂. N₂ arises presumably from cyanate ion decomposition. Decarbonation of these apatites occurs in three steps, the first of these is attributed to carbamate ions.     

Etude theorique des proprietes thermodynamiques du radical CN et de ses dimeres

Using the ab initio LCAO—SCF—MO method and the 6–31G extended basis set, the CN radical and its possible dimers (NCCN, CNNC or CNCN) have been studied in terms of nuclear equilibrium geometries, normal modes of vibration, IR spectrum and thermodynamic properties. The results show that quantum chemical calculations enable these parameters to be obtained with adequate accuracy. Working properly, one can build a local potential energy surface on which to perform a harmonic vibrational analysis. Hence all the required information to apply the principles of statistical thermodynamical analysis is available.     

Etude theorique de la reactivite des ions libres intervenant dans la polymerisation anionique de quelques monomeres vinyliques

The reactivities have been calculated for free ions involved in anionic polymerization of vinyl monomers. The copolymerization constants k_AB available in the literature are compared to the stabilization energies involved in the reaction of carbanions with the same monomer. The reactivities of carbanions of living poly (2-vinyl pyridine), poly styrene and poly (substituted styrenes) with respect to 1-1,diphenylethylene have been computed. The rate constants of homopolymerisation have been compared with the variation of π energy between the “monomer” and “carbanion” states of these monomers. The occurrence of side-reactions during the polymerization of vinyl-pyridine has been investigated using quantum chemistry methods.     

Etude cinetique d'une decomposition thermique par couplage de la calorimetrie et de l'analyse thermique a vitesse de decomposition constante

A method is described where the simultaneous measurement of a thermal flow (by means of Tian-Calvet type calorimetry) and of a gas flow (by means of constant decomposition rate thermal analysis) allows the knowledge at any time of the instantaneous enthalpy of thermal dissociation. The method is used to study the thermal decomposition of an industrial Al(OH)₃ gibbsite sample.     

Etude de la permittivite complexe d'ellipsoïdes disperses dans un milieu continu. Analyses theorique et numerique

Resumé Les lois de mélange classiques valables en général pour de très faibles fractions volumiques en matière dispersée sont étendues aux fortes concentrations par la méthode de Bruggeman. On indique les relations obtenues pour la distribution aléatoire d'ellipsoïdes au sein d'un milieu continu. Le cas des ellipsoïdes anisotropes est considéré ainsi que celui des systèmes multidispersés á plusieurs constituants.En illustration on a étudié par analyse numérique le cas des ellipsoïdes isotropes de révolution dispersés dans un milieu isolant en mettant l'accent sur l'influence du rapporta/b des demi-axes.

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Blending laws derived for very small volume fractions of dispersed medium are extended to high concentrations, using Bruggeman method. Derivation is made in the case of a random distribution of ellipsoids dispersed in a continuous medium. The case of non isotropic ellipsoids and the case of multicomponent systems are also considered.As an example, a numerical analysis is made in the case of isotropic ellipsoids of revolution dispersed in an insulating medium; particularly, the effect of the semi-axis ratioa/b is pointed out.

     

Etude theorique de la cycloaddition de la nitrone sur l'ethylene

A theoretical study of the concerted 1,3-dipolar cycloaddition of nitrone on ethylene has been carried out by the LCAO-SCF-MO method. The potential energy hypersurface for the reaction has been investigated and the characteristics of the transition state have been determined.     

Etude theorique de la cycloaddition dipolaire 1–3

A theoretical study of the 1,3-dipolar cycloaddition reaction of: diazomethane with ethylene has been carried out by the LCAO-SCF-MO method. The potential energy hypersurface for the reaction and the electronic structure of the transition state have been investigated.     

Etude des reactions pericycliques sous pression—IV: Cyclodimerisation thermique de l'acroleine et de la methylvinylcetone

The thermal cyclodimerization of acrolein with methyl vinyl ketone gives selectively only one substituted dihydropyran. The rate is only slightly sensitive to the nature of the solvent; however a slight decrease of the reaction rate with increasing solvent polarity was observed. Effects of high pressure give strong support for a one-step mechanism and the formation of a transition state more compact than the adduct.     

Etude par des methodes semi-empiriques de la chimie theorique dans la serie des pyrazolones—VII : Sur le probleme de la tautomerie des phenylazopyrazolones

The tautomeric equilibrium, configuration, bond order P_CO and structure of the common anion of phenylhydrazopyazolones have been investigated by means of semi-empirical MO methods (Hückel-ω, Extended Hückel). The results have been compared with those in the literature. Experiments have been made in order to verify the theoretical predictions.     

Interpretation theorique de la reaction de diels-alder dans la serie des dienes fonctionnels dissymetriquement substitues-II : Etude des mecanismes de reaction par calcul mindo des etats de transition

The different behaviour of two 1- or 2-ethoxy butadiene isomers with respect to acrolein in the Diels-Alder reaction is explained on the basis of reaction mechanisms. Using MINDO/2 calculations, various models of the transition state are investigated and geometric parameters for each reaction path coordinate are optimized. The choice of a model describing the transition state is given by the corresponding potential barrier height, which characterizes the approach of reagents and the site of the functional of the diene. Its lowest value corresponds to a concerted reaction mechanism with acrolein; a synchronous mechanism is found for 2-ethoxy butadiene, and a two-stage one for 1-ethoxy butadiene. The variation in barrier height in the two systems is well correlated with the corresponding change in the observed reaction rate.