503 research outputs found
Contribution of microreactor technology and flow chemistry to the development of green and sustainable synthesis
No full textMicroreactor technology and flow chemistry could play an important role in the development of green and sustainable synthetic processes. In this review, some recent relevant examples in the field of flash chemistry, catalysis, hazardous chemistry and continuous flow processing are described. Selected examples highlight the role that flow chemistry could play in the near future for a sustainable development
Flow chemistry as enabling technology for controlling the reactivity of fluorocarbenoids
No full textFluorinated compounds have attracted a great deal of interest by scientists involved in many field of science and technology. However, despite their importance, the selective introduction of monofluoromethyl groups (-CH2F) into a small organic molecules is still a challenging task. Unlike the extensive use of other halocarbenoids in organic synthesis, fluorocarbenoids are still considered the "beast" in carbenoid chemistry due to their chemical instability that severely limited its use in synthetic process. In this communication, we report how we tried to face this challenge by employing flow microreactor technology. Fluorocarbenoids could be effectively generated and trapped with electrophiles providing a new successfully application of flash chemistry in short-lived intermediate reactions. Mechanistic insights and applications will be presented
Combined powder X-ray diffraction data and quantum-chemical calculations in EXPO2014
No full textThis paper describes new features implemented in the EXPO2014 software and aimed at assisting crystallographers in the use of quantum-chemistry calculations in combination with experimental powder diffraction data. The implemented tools are useful in particular in two important steps of the process of crystal structure determination from powder diffraction data: (1) preparing accurate structural model suitable for crystal structure determination by real-space methods; (2) validating structure determination. The combination of experimental/quantum-chemical methods in EXPO2014 is now managed easily thanks to the following capabilities: (a) converting crystallographic data in input files and reading molecular geometry from output files of a wide variety of computational chemistry packages (GAMESS-US, NWChem, Gaussian, CRYSTAL, ABINIT, QUANTUM ESPRESSO); (b) optimizing the geometry of a molecule using Open Babel's force fields; (c) a graphical interface to run semi-empirical quantum calculation by MOPAC (Molecular Orbital PACkage); (d) producing input file for dispersion-corrected density functional theory
Functionalization of four-membered cyclic sulfoximines by a convenient lithiation/trapping sequence
No full textThe functionalization of four-membered cyclic sulfoximine, based on a lithiation/electrophile trapping sequence, led to unprecedented
C(2)-substituted N-Boc-1-imino-16-thietane 1-oxide in moderate to good yields. Interestingly, the reaction proceeded with high
stereocontrol showing a preferential bias for an introduction of the electrophile syn to the oxygen on the sulfur. Starting from thietan-
1-one, by a combination of lithiation/electrophile trapping followed by N-transfer, it is possible to obtain the stereoisomer bearing the
electrophile syn to the nitrogen on the sulfur. Thus, all stereoisomers can be accessible for medicinal chemistry studies
External Trapping of Halomethyllithium Enabled by Flow Microreactors
No full textThis work demonstrates that the accurate control of the reaction parameters realized within microreactor systems allowed for a taming of the reactivity of thermally unstable intermediates such as haloalkyllithiums. The first example of effective external trapping of a reactive carbenoid such as the chloromethyllithium is described. By using microreactor systems, a continuous flow synthesis of chloro alcohols and chloro amines could be achieved with high yields. By controlling the residence time the highly reactive chloromethyllithium could be generated and reacted with electrophiles at temperatures much higher than in batch‐mode and without internal quenching. The developed continuous‐flow process matches the requirements for sustainability
El Tlacuache Núm. 365 (2009). 365 Año 9 (2009) mayo. El Tlacuache
No full textRubén Jaramillo: las intenciones del crimen por Aura Hernández. - Jaramillo y la disputa el sentido de la vida por Flavio Barbosa. - De campesinos a obreros: una comunidad surgida entre las flores por Rafael Gutiérrez
Comparison among possible design solutions for the Stray Field Shielding System of the DTT Neutral Beam Injector
No full textWithin the effort on the conceptual design of the Divertor Test Tokamak (DTT) Neutral Beam Injector (NBI), the design of the Stray Field Shielding System (SFSS) for DTT NBI is under development, to suppress the potentially harmful effects of the stray poloidal field from the tokamak on the accelerated charged beam. Various possible design solutions to solve this problem are presented and compared, with a particular focus on the stray field minimization procedure and particle tracing simulations, used during the design validation phase with the objective of maximizing beamline performances
Personnalisation et leadership Le cas du Mouvement Cinq Étoiles
No full textThe article draws a characterisation of the late comer among the Italian populist parties, the Five Star’ Movement, led by the ancient comedian Beppe Grillo. Starting with a definition of what he means by “political personalisation”, the Author first describe this party as a political organisation in which the leader masters all the key areas – notably, communication, rules setting, and resolution of internal conflicts. Then, he argue that the Five Star Movement is a “personalist party”, in which Beppe Grillo embodies a powerful but non-charismatic leader. In the closing section, the Author tries to shed light above the probable evolutions of the party, particularly dealing with its institutionalisation process
A direct and sustainable synthesis of tertiary butyl esters enabled by flow microreactors
No full textTertiary butyl esters find large applications in synthetic organic chemistry. A straightforward method for the direct introduction of the tert-butoxycarbonyl group into a variety of organic compounds has been developed using flow microreactor systems. The resultant flow process was more efficient, versatile and sustainable compared to the batch
Microreactor as enabling technology for taming highly reactive metal fluorocarbenoids
No full textFluorinated compounds have attracted a great deal of interest by scientists involved in many field of science and technology. However, despite their importance, the selective introduction of monofluoromethyl groups (-CH2F) into a small organic molecules is still a challenging task. The selective nucleophilic monofluoromethylation could be accomplished through two main strategies: a) the direct transfer of a “CH2F” moiety into organic molecules; b) the transfer of the fluorinated group linked to a suitable auxiliary which should be removed at the end of the sequence. To date, the limited chemical stability of fluoromethyl carbanions has been efficiently overcome by taking advantage of the stabilizing effect displayed by strong electron-withdrawing functionalities. In striking contrast, the use of a simple M-CH2-F reagent (M = metal) would represent a straightforward method for the direct one-pot functionalization of a given electrophile. Nevertheless, fluorocarbenoid is still considered the "beast" in carbenoid chemistry due to its chemical instability that severely limited its use in synthetic processes. In this communication, we report how the use of engineered PI microreactors and flash chemistry allowed for the generation and use of metal fluorocarbenoids under “external quenching conditions” which seems to be prohibitive under traditional batch conditions
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