Suchergebnisse

In the first paper of this series, the aminolysis of the derivates of ϐ-ethylthiovinyl-2 cycloammoniums was investigated at low concentration (4. 10-5 ML-1) and a general reaction scheme was given.
In the present publication, catalytic activities of various anions and different solvents were evidenced and submitted to a quantitative study. The global anion effect was looked at, by adding the corresponding tetraethyl-ammonium salts (Cl-, Br-, I-, CIO-4, PF-6 , BF-4 , NO-3, p — CH3 — C6H4 — SO-3, B(C6H5)-4). As an example, p-cyanoaniline (8.55. 10-2 ML-1) reacts with ϐ-ethylthiovinyl-2 triméthyl-1,3,3 indoleninium 4.4.103 times faster in the presence of tetraethylammonium chloride (2.91.10-1 ML-1) than in the absence of this salt. Actually, the anions Cl-, Br-, NO-3, I-, p — CH3 — C6 — H4SO-3 are active, whereas B(C6H5), BF-4, PF-6, CIO-4 are ineffective.
The global salt effect can be separated in two different actions : a base catalysis (proton transfer) and a solvatation effect (hydrogen bonding). These results were achieved in determining the various kinetical parameters at 25 °C under different conditions.
The basicity of the solvents, as ΔvD, can be correlated with the reaction velocity (expressed as logk1k2a/k-1) in a free energy linear relationship at
about the same dielectric constant. As a conclusion, to fasten the reactions of this kind, it is advisable to use basic solvents as NN'dimethylacetamide and basic anions as Cl-.

Le grand nombre et la grande variété des titres de bande-dessinée noire dont le scénario traite, tout ou partie, des relations internationales invitent le chercheur, et non moins lecteur assidu, à se pencher sur cet objet particulier d'histoire culturelle. Il s'agit d'en comprendre les spécificités quant au traitement de l'événement historique, entre fiction et réalité, mais aussi le poids de la circulation des images et des récits. Cette enquête invite également le chercheur à repenser son positionnement et son rapport au sujet qu'il traite.