Étude de la cinétique de la dégradation thermique du polypropylene et du polystyrène par analyse thermogravimétrique

Kinetic studies on the thermal degradation of polypropylene and polystyrene have been carried out using the thermogravimetric technique. Experimental thermograms have been interpreted by means of a simulation model which takes into account several simultaneous or consecutive reactions. In nitrogen, polypropylene degradation involves two reactions. The activation energy calculated for the second reaction, which corresponds to the main part of the weight loss curve, agrees with values obtained by means of calculation methods based on only one overall reaction. In air, a third reaction is added. Its activation energy is also in agreement with published values. However, for the two studied materials, orders of reaction are different.     

Unimolecular gas-phase reactions of the methyl acetoacetate radical cation. Oxygen atom permutation via ion-molecule complexes

The reactions of metastable decomposing methyl acetoacetate (a mixture of keto a ad enol tautomers) are reported and discussed. The unimolecular fragmentations of the tautomers are different. The metastable decomposing radical cation of the keto form displays four specific ions: [M –CO]⁺˙, [M – CH₂O]⁺˙, [M – CH₂CO]⁺˙ and m/z 43. The results derived from D-, ¹³C- and ¹⁸O-labelled precursors together with thermochemical data have been used to study the mechanisms. Experimental results indicate that an unexpected isomerization occurs before dissociation. It formally corresponds to oxygen atom permutation of the two carbonyl groups without participation of the carbon atoms. This remarkable process is interpreted in terms of a mechanism involving ion-molecule complexes.     

Synthesis of new 4-(1-ethylthio-2,2,2-trifluoroethyl)-6-methylpyridazin-3(2H)-ones starting from S-ethyl 4-oxo-2-(pentafluoroethyl)pentanethiolate and hydrazines

The paper presents a one-pot conversion of γ-keto-α-pentafluoroethyl thioester into new pyridazin-3-ones and α,β-unsaturated lactams. The structures of all new compounds were ascribed using 1D (¹⁹F, ¹H, ¹³C) and 2D (¹H-¹⁵N) NMR data, and X-ray diffraction analysis. Two possible competitive reaction mechanisms for the synthesis of pyridazin-3-ones and lactams are presented.     

Cadmium speciation in Arabidopsis thaliana as a strategy to study metal accumulation system in plants

The strategy to identify cadmium deactivation mechanism in Arabidopsis thaliana has been developed using selective and sensitive hyphenated techniques. Cadmium concentrations, in main parts of the plant, were determined by ICP-MS and total amount was found as 0.43-0.44 μg g⁻¹ in leaves and 3.3-3.4 μg g⁻¹ in roots. Speciation of the metal complexes in cells was investigated by SEC-ICP-MS in order to estimate the accumulation process. Phytochelatins, desglycyl-phytochelatins and phytochelatins homologues lacking the N-terminal γ-linked glutamic acid were extracted from plant and were identified by RPLC-ESI-MS. Two-dimensional chromatography allowed to link the metal complexes separated by SEC with isoforms of phytochelatins analyzed by high resolution RPLC and confirm their significant responsibility for metal accumulation. The potential of the cadmium complexes speciation indicates that obtained results could be reliable source of knowledge to confirm the information coming from the well-known genomic sequence of Arabidopsis and to estimate the role of γ-glutamyl transpeptidase in metabolism of glutathione.     

Additional of functional vinylzinc reagents to nitrones: synthesis of (E)-N-allylhydroxylamines and their rearrangement into (E)-O-allylhydroxylamines

The vinylzinc reagents derived from hydrozirconation of alkynes and transmetallation add readily to nitrones to yield pure (E)-N-allylhydroxylamines; some of these rearrange into O-allylhydroxylamines.     

Gas-phase structures and mass spectra of binary pentafluorides

Most known non-radioactive pentafluorides have been examined by molecular-beam mass spectrometry and by the deflection of molecular beams in inhomogeneous electric fields. Extensive association of the vapors occurs for all but the lighter pentafluorides and the interhalogens. The interhalogen pentafluorides are strongly polar, consistent with the accepted C_4v symmetry. The transition-metal and Group V pentafluorides are all non-polar, except VF₅ and CrF₅ for which temperature-dependent polarity is observed. However, uncertainty exists as to whether these observations are applicable to monomeric pentafluorides in all cases. Mass-spectral cracking patterns are presented for all species.     

Effects of structural factors on the pi-dimerization and/or disproportionation of the cation radical of extended TTF containing thiophene-based pi-conjugated spacers

The electrochemical and chemical oxidation of extended TTF 4 and 5 are analysed by cyclic voltammetry, Visible/NIR and ESR spectroscopies, and the X-ray structures of the new salts 5 x BF(4)(CH(2)Cl(2)) and 4 x ClO(4)(THF)(1/2) are presented. The effects of structural factors on the pi-dimerization or the disproportionation reaction of the cation radical are shown. The oxidation of compound 4 presents the successive formation of stable cation radical and dication species both in dichloromethane (DCM) and in a CH(3)CN/THF mixture. In contrast, for compound 5, the stability of the oxidation states strongly depends on the nature of the solvent. In DCM, the oxidation of 5 proceeds by two close one-electron transfers while in CH(3)CN/THF the dication is directly formed via a two-electron process. The X-ray structures of the two salts reveal the formation of pi-dimers of cation radical. While the dimer (5(2))(2+) is due mainly to pi-pi interactions between the conjugating spacer, the multiplication of the sulfur atoms in compound 4 contributes to stabilize the dimer by the combined effects of S-S and pi-pi interactions. Visible/NIR and ESR experiments confirm the higher tendency of 4(+)(.) to dimerize with the occurrence of dimer and monomer in solution, while for 5(+)(.) only the monomer is detected in DCM. On the other hand, by dissolution of 5 x BF(4)(CH(2)Cl(2)) in CH(3)CN, only the neutral and the dicationic states of compounds 5 are observed owing to the disproportionation reaction.     

Template-Reaktion von Bis(acetylacetonato)-dioxo-molybdän(VI) mit Benzoylhydrazin

Template Reaction of Bis(acetylacetonato)-dioxo-molybdenum(VI) with Benzoylhydrazone By reaction of bis(acetylacetonato)-dioxo-molybdenum(VI) with benzoylhydrazine benzoylhydrazido(2?)-acetylacetonebenzoylhydrazonato(2?)-oxo-molybdenum(VI) was formed beside another species. The compound was characterized by mass spectrometry and X-ray structural analysis. Crystallographic data see ?Inhaltsübersicht”?.     

低温燐光的研究及应用

本文综述了44篇文献,介绍低温燐光的发展概况及其应用。