Méthylénation et diazotisation en chimie en flux continu

Les composés diazoïques sont des produits contenant une molécule de diazote dans leur structure. La libération de cette molécule de diazote est thermodynamiquement favorisée, ce qui en fait des composés très réactifs. Pour cette raison, ce sont des composés très utilisés en synthèse organique notamment pour la formation d’esters ou dans des réactions catalysées par des métaux de transitions comme des cyclopropanations ou des méthylénations. Cependant, le fait de contenir une molécule d’azote confère également à ces composés une énergie élevée, ce qui les rend potentiellement explosifs. De plus ces composés présentent généralement une toxicité élevée. Ces considérations sont d’autant plus importantes lorsque l’échelle augmente. Pour éviter la manipulation de ces réactifs dangereux, les chimistes ont développé différentes alternatives. La génération in situ de ces composés est une des approches classiques des plus courantes. La chimie en flux continu ou en débit continu est une technologie qui permet la manipulation sécuritaire de produits dangereux. De ce fait, la chimie en flux continu s’est imposée comme une alternative sécuritaire pour la génération, la manipulation et l’utilisation des composés diazoïques. Une réaction de méthylénation catalysée par des métaux de transition a été développée il y a quelques années dans le groupe du Pr. Lebel. Cette réaction utilise un composé diazoïque, le TMS-diazométhane, qui est connu pour être très toxique. De ce fait, la réaction de méthylénation a été transposée en chimie en flux continu afin de développer un procédé plus sécuritaire. Différentes approches ont été explorées afin d’améliorer cette réaction en flux continu. Par la suite, une nouvelle méthodologie de synthèse du TMS-diazométhane par diazotisation a été développée. Après avoir développé la synthèse de l’amine sur grande échelle grâce à l’utilisation de la chimie en flux continu, la synthèse du TMSCHN2 a été réalisée. Le développement d’une purification du TMSCHN2 pouvant être réalisées en flux continu, a permis d’obtenir un procédé rapide, efficace et adaptable sur grande échelle. Le développement de la génération in situ du TMS-diazométhane afin de réaliser des estérifications a par la suite été investigué. Cette approche a débouché sur une méthodologie plus générale d’estérification par diazotisation in situ d’amines. Cette méthodologie permet de synthétiser une grande variété d’esters avec de bons rendements et donne une excellente chimiosélectivité. Des études mécanistiques ont par la suite été réalisées pour définir le mécanisme exact de la réaction.Diazo compounds are products containing a molecule of nitrogen in their structure. The nitrogen release is thermodynamically favored making diazo compounds highly reactive. As such, diazo compounds are widely used in organic synthesis, in particular for the formation of esters or in transition metal-catalyzed reactions such as cyclopropanations or methylenations. However, the high energy property associated with diazo compounds makes them potentially explosive. In addition, the diazo compounds generally display a high toxicity. Such considerations are even more important on large scale. To avoid handling dangerous reagents, alternatives have been developed by chemists. In situ generation of diazo compounds is one of the most common classical approaches. Continuous flow synthesis is a technology that allows for the safe handling of hazardous products. As a result, continuous flow chemistry has emerged as a safe alternative for the generation, manipulation and use of diazo compounds. A transition metal-catalyzed methylation reaction was developed a few years ago by Prof Lebel's group. The reaction uses a diazo reagent, TMS-diazomethane, which is known to be very toxic. As a result, the methylenation reaction has been transposed into continuous flow chemistry in order to develop a safer process. Different approaches have been explored to improve the continuous flow methylenation process. Subsequently, a new methodology for the synthesis of TMS-diazomethane by diazotization has been developed. After having developed the amine synthesis on a large scale in continuous flow chemistry, the synthesis of TMSCHN2 was investigated. Moreover, the purification of the obtained solution can be carried out in continuous flow. The overall process produces the TMSCHN2 in a fast and efficient manner. Furthermore, the methodology is easily adaptable on a large scale. The development of the in situ generation of TMS-diazomethane in order to perform esterifications has subsequently been investigated. The approach has resulted in a more general methodology for esterification by in situ diazotization of amine. Various esters were synthesized in good yields and with excellent chemoselectivities. Mechanistic studies were performed to define the exact mechanism of the reaction

À MemÓria De Paul Teyssier

Elogio fúnebre do Professor Paul TEYSSIER pronunciado por seu discípulo e amigo Albert AUDUBERT, ex-professor de Língua e Literatura Francesas na Univerisdade de São Paulo, por ocasião da missa celebrada no dia 29 de janeiro de 2002 pelo reverendo ARMOGATHE, capelão da École Normale Supérieure, na igreja de SaintSéverin, em Paris.42

O Renascimento Francês

Não gostaríamos de começar esta palestra com uma heresia talvez em relação à História, mas, em literatura pode-se dizer que as gerações, como as pessoas, têm muitas vêzes consciência de sua idade . Na época romântica, por exemplo, muitos grandes poetas sentem-se velhos ou cansados — é o famoso mal du siècle (mal do século) .

À memória de Paul Teyssier

Elogio fúnebre do Professor Paul TEYSSIER pronunciado por seu discípulo e amigo Albert AUDUBERT, ex-professor de Língua e Literatura Francesas na Univerisdade de São Paulo, por ocasião da missa celebrada no dia 29 de janeiro de 2002 pelo reverendo ARMOGATHE, capelão da École Normale Supérieure, na igreja de SaintSéverin, em Paris

Solid state synthesis and X-ray diffraction characterization of Pu 3+(1-2x)Pu4+xCa2+xPO4

In the framework of the 1991 French law concerning nuclear waste management, several studies have been carried out in order to elaborate crystalline matrices for specific immobilization of the radionuclides. In the case of high level and long-lived minor actinides (Np, Am and Cm), which are high level and long-lived radioactive elements, monazite, a light rare earth (Re) orthophosphate with general formula Re3+PO4 (with Re = La to Gd), has been proposed as a host matrix, thanks to its high resistance to self irradiation and its low solubility. Monazite crystallizes in the monoclinic space group P21/n. In this structure, trivalent cations (Re3+) could be substituted by an equivalent amount of bivalent (A2+) and tetravalent (B4+) cations, allowing the simultaneous incorporation of Am3+, Cm3+ and Np4+. According to Podor's work1, the limit of a tetravalent element incorporation in monazite is related to its size in the ninefold coordination (RIX)

Synthesis and characterization of thorium-bearing britholites

RADIOCHIn the field of the immobilization of tri- and tetravalent minor actinides, apatites and especially britholites were already proposed as good candidates. In order to simulate tetravalent minor actinides, the incorporation of thorium, through dry chemical routes, was studied in britholite samples of general formula Ca9Nd1−xThx(PO4)5−x(SiO4)1+xF2. The study showed that the incorporation of thorium was effective whatever the thorium reagent used or the grinding conditions considered. Nevertheless, it appeared necessary to use mechanical grinding (30 Hz, 15 min) before heating treatment (T = 1400 °C, 6 h) to improve the reactivity of powders and the sample homogeneity. In these conditions, the incorporation of thorium in the britholite structure occurred above 1100 °C. The heating treatment at 1400 °C led to single phase and homogeneous compounds. This work also underlined the necessity to prefer the coupled substitution Click to view the MathML source instead of (Nd3+, F−) left right double arrow (Th4+, O2−) in order to prepare pure and single phase samples in all the range of composition examined

Volume interdiffusion coeffcient and uncertainty assessment for polycrystalline materials

A method has been developed in order to assess small volume interdiffusion coeffcients from experimental Electron Probe MicroAnalysis concentration profiles of polycrystalline materials by means of Boltzmann-Matano or den Broeder methods and their complementary Hall method. These methods have been used as tools for the investigation of the quasi-binary UO2/U(1-y)PuyO(2-z) interdiffusion, for which obtaining a solid solution in the bulk of grains is of major interest. In this paper uncertainties on the interdiffusion coefficient as a function of concentration have been computed for each method. Small volume cofficient measurements were enhanced by means of a small angle acquisition profile line with respect to the interdiffusion interface

Heavy ion induced damages in Ti3SiC2: study of the swelling

International audienceFor Generation IV reactors, and more particularly the Gas Fast Reactor, ternary carbide Ti3SiC2 is an interesting candidate for the application as fuel coating; actually, it has the advantage to combine some properties of metals with those generally attributed to ceramics. Unfortunately, few data are available on its behavior under irradiation. In this study, we attempted to measure and to understand the origin of the swelling induced by nuclear collisions. Thus, it seems that Ti3SiC2 irradiated at room temperature swell less than silicon carbide and that critical amorphization temperature is less than room temperature

Formation of nanosized hills on Ti3SiC2 oxide layer irradiated with swift heavy ions

International audienceThe Ti3SiC2 refractory compound that combines properties of both metals and ceramics is a fuel cladding candidate under investigation for Gas-cooled Fast Reactor. Its behavior under swift heavy ion irradiation (Xe ions, 92 MeV, 1019 m−2) was investigated. Significant and unexpected surface changes have been highlighted: hills have been observed by AFM on the surface of Ti3SiC2. Such a topographic modification has never been observed in other materials irradiated in similar conditions. The characterization of these hills by both XPS and X-TEM has highlighted that the surface modifications do not appear in Ti3SiC2 but in the amorphous oxide layer located on the sample surface before irradiation. Moreover, the thickness of this oxide layer grew under irradiation dose. The comparison with previous irradiations has led to the conclusion that this surface modification stems from electronic interactions in this amorphous layer, and that there is a threshold in the electronic stopping power to overcome to form hills