J.J. Villenave

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

Abstract 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. X. Decompositions simultanees spontanee et induite du peroxyde de benzoyle en solution

Abstract The kinetics of the thermal decomposition of benzoyl peroxide in dibutyl phthalate solvent were studied by differential scanning microcalorimetry. Mathematical treatment of the enthalpimetric curves obtained for several different initial concentrations led to as an experimental rate law. From the kinetic studies and analysis of the products of some isothermal decompositions a reaction mechanism was proposed. Both spontaneous and radical induced decompositions were found to occur; their rate constants and activation parameters were easily computed from the results of the non-isothermal kinetic determinations.

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

Abstract 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. 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

Abstract 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. III. Probleme de la non correspondance entre temperatures mesurees et constantes de vitesse

Abstract Rate constants of the free radical decomposition of AIBN have been determinated in different solvents using a differential scanning microcalorimeter at several temperature programmes. They seem to depend on the heating rate; but this is explained by the existence of a difference in temperature between the studied solution and the position at which θ is measured. At low heating rate, there is agreement between real and measured temperatures and, thus, fair correspondence between rate constants and temperatures observed.

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

Abstract 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 en programmation de temperature. VI. Thermolyse d'azo-1,1′-(cyano-1 cyclanes) dans differents solvants

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

Abstract 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 programmation de temperature. IV. Parametres cinetiques del l'homolyse de l'azo-bis-isobutyronitrile en solution

Abstract 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 (Δ G ≠ ) is proposed as a characteristic of the thermal stability of free-radical initiators.

Synthese d'aldehydes γ-fonctionnels par voie radicalaire

Resume The addition of radicals issued from the solvent to the double bond of O,O-t-butyl and O-vinyl peroxycarbonate results on the free-radical induced decomposition of this peroxyester and offers an original synthetic route for γ-functional aldehydes.