INFLUENCE OF THE EXPERIMENTAL SYSTEM AND OPTIMIZATION OF THE SELECTIVITY FOR THE ELECTROCARBOXYLATION OF CHLOROACETONITRILE TO CYANOACETIC ACID

The electrocarboxylation of chloroacetonitrile (ClACN) to cyanoacetic acid in undivided cells equipped with sacrificial anodes was investigated both in a bench-scale electrochemical batch reactor and in a continuous batch recirculation reaction system equipped with a parallel-plate electrochemical cell. Selectivity and faradaic yields higher than 90% were obtained by working under anhydrous conditions with low halide concentrations and at more negative potentials. It was found that the instantaneous selectivity in the carboxylate compound depends mainly on the [CO2]/[ClACN] ratio at high substrate concentration and is close to 100% for low ClACN concentration. These results were consistent with the previsions of a semiempirical model based on the assumption that under adopted experimental conditions the selectivity of the process is mainly determined by the competition between two very fast reactions: the carboxylation and a father-son reaction between the electrogenerated anion and the substrate. The effect of the nature of the solvent and of the concentration of proton donor species was further investigated

Premier bilan des recherches sur la pierre de construction à Mégara Hyblaea

Dans cet article, on propose un premier bilan des recherches préliminaires sur la pierre de construction à Mégara Hyblaea, fruits des travaux communs d’une équipe d’archéologues et de géologues. Les analyses pétrographiques d’échantillons représentatifs de l’architecture en pierre de Mégara ont d’abord montré que trois types de roche avaient été utilisés : il s’agit de calcarénites appartenant à des formations géologiques locales du Pléistocène et du Miocène. Dans le territoire de Mégara, on a ensuite identifié plusieurs anciennes carrières comme possibles sites d’extraction. Parmi celles-ci, trois possèdent des faciès géologiques parfaitement compatibles avec ceux des échantillons archéologiques : l’Intagliata, la Pirrera di Melilli et la côte Nord de la presqu’île de Thapsos.In this article, we offer a first assessment of the preliminary research on the construction stone in Megara Hyblaia, fruit of the joint works of a team of archaeologists and geologists. The petrographic analysis of representative samples of Megara’s stone architecture have first shown that three types of stone had been used: all three are calcarenites belonging to local Pleistocene and Miocene geological groups. In Megara’s territory, we have then identified several ancient stone quarries as potential extraction sites. Three of them bear geological features matching perfectly those of the archaeological samples: the Intagliata, the Pirrera di Melilli and the north coast of the Thapsos peninsula

Premier bilan des recherches sur la pierre de construction à Mégara Hyblaea

International audienc

Electrically conductive hydrogel composites made of polyaniline nanoparticles and poly(N-vinyl-2-pyrrolidone)

A novel electrically conductive composite material, consisting of polyaniline (PANI) nanoparticles dispersed in a polyvinyl pyrrolidone (PVP) hydrogel, was prepared ‘in situ’ by water dispersion polymerisation (DP) of aniline using PVP as steric stabiliser, followed by g-irradiation induced crosslinking of the PVP component. Conversion yield of aniline into PANI particles was determined via HPLC and gas chromatography, while structural confirmation of the synthesised polymer was sought by FTIR. Morphology and dimensions of PANI particles into the coloured, optically transparent hydrogel was determined by electronic microscopy; moreover, swelling behaviour of composite hydrogels in different buffer solutions was investigated by gravimetric measurements and compared to that of pure PVP hydrogels. Cyclic voltammetry experiments were carried out both on these hydrogels and on the parent aqueous dispersions, at different pH values of the suspending/swelling medium, while conductivity of the composite hydrogels was derived from Impedance Spectroscopy; in both cases results were compared to those relative to hydrogels containing commercial-grade PANI particles