Étude théorique de la structure électronique et de la géométrie moléculaire de la benzylidène-aniline

La structure et les transitions électroniques de la benzylidène-aniline dans différentes conformations ont été étudiées par la méthode ASMO-CI dans l’approximation semi-empirique de Pariser et Parr avec l’inclusion des électrons n de l’azote. Les prévisions du calcul permettent une interpretation complète des spectres électroniques en ce qui concerne les énergies et les intensités des transitions. L’angle de rotation autour de l’axe de la liaison C—N parait être, en solution, inférieur à celui de 55° qu’on a trouvé à l’état cristallin

Kinetic Modeling of the Formation and Destruction of Polychlorinated Dibenzo‑<i>p</i>‑dioxin and Dibenzofuran from Fly Ash Native Carbon at 300 °C

The kinetics for the oxidative breakdown of native carbon in raw fly ash samples (RFA) and for the formation and destruction of polychlorinated dibenzo-<i>p</i>-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), abbreviated PCDD/F, were investigated using a flow-over solid system in which the RFA samples were thermally treated at 300 °C under synthetic air. This study investigated the correlation between the disappearance of the reagent and the formation of the products to gain insight into the underlying mechanisms that govern these reactions at congener groups level.The detailed analyses of the experimental concentration–time data revealed significant differences in the behavior between the 2,3,7,8-substituted PCDD and the 2,3,7,8-substituted PCDF, non-2,3,7,8-substituted PCDD and PCDF. The chlorine balance for the former was always negative, that is, chlorine was released regardless of reaction time and primarily resulted from the dechlorination of the hepta- and octa-homologues. However, for the others, the balance was substantially positive up to approximately 240 min and became negative at longer intervals when the dechlorination reactions took over.The processes involving PCDD and PCDF in which the thermal destruction was only partial were found to increase the total equivalent toxicity (TEQ) levels rather than reduce them

Experimental and Theoretical Investigation on the Catalytic Generation of Environmentally Persistent Free Radicals from Benzene

Environmentally persistent free radicals (EPFRs) are toxic products deriving from incomplete combustion and are able to generate DNA damage and pulmonary dysfunction. They are formed on particulate matter through interaction with aromatic hydrocarbons, catalyzed by transition metal oxides, and produce reactive oxygen species (ROS) in aquatic media. The processes are already described for substituted aromatic molecules, for example, phenol, but not for unsubstituted aromatic systems, such as benzene. This Article reports on the reaction of benzene with molecular oxygen in the presence of CuxO/SiO2, suggesting a mechanism based on cluster and periodic computational models. The activation of O2 by interaction with silica coordinated Cu(I) centers leads to a peroxy species that yields the phenoxy radical upon reaction with benzene. Dissociation of OH• radical eventually allows for the recovery of the catalyst. The experimental characterization of the CuxO/SiO2 catalyst regarded morphology, crystal structure, copper electronic state, and crystal field around Cu(II). Electron paramagnetic resonance (EPR) spectroscopy revealed the formation of phenoxy radical entrapped in the catalyst upon reaction between benzene and CuxO/SiO2. Moreover, EPR investigation of ROS in aqueous solution evidenced the generation of OH• radicals by benzene-contacted CuxO/SiO2. All of the experimental results nicely fit the outcomes of the computational models