Actualités

15 juin 2016

Café des Sciences de PROMES - SOLSTICE le mardi 21 juin à 14h, salle des conférences de PROMES/Tecnosud - Karine LOUBIERE


Le prochain Café des Sciences intitulé:
"Ingénierie des réacteurs dédiés à la photochimie préparative : méthodologies d'intensification via l'utilisation de technologies microstructurées"
donné par:
Karine Loubière
Laboratoire de Génie Chimique UMR 5504, Toulouse
aura lieu le mardi 21 juin, 14H, salle de conférences de PROMES/Perpignan.

Organic photochemistry is becoming a key synthesis pathway in sustainable chemistry [1]. In contrast to thermal reactions, photochemical reactions are induced via the electronically excited state possessing a different electron configuration than their corresponding thermal ground states. Consequently, the chemical reactivity of excited molecules is considerably different from that of ground state molecules. The following points are particularly interesting in the context of sustainability: (i) multi­step syntheses of complex molecules are shortened and simplified; often, a high molecular complexity is generated in one step from simple precursors, (ii) a portfolio of novel compound families (e.g. strained rings) is becoming accessible or more easily accessible, and (iii) in many reactions, the photon acts as a “traceless reagent”, and no chemical catalysts (acid, base, metal, etc.) or activating groups are needed [2].

At the same time, continuous­flow technologies, in particular microstructured reactors, have emerged as alternatives to batch processing and their implementation in process intensification strategies is likewise crucial for sustainable chemistry [3]. Recently, various works have shown that these technologies are also suitable and beneficial for preparative photochemistry, boosting the interest in continuous­flow photochemistry [4­6].

The present presentation aims to illustrate that some of the current challenges and issues in continuous­flow photochemistry can be addressed using a chemical engineering framework [7]. Such a framework is indeed essential to elaborate a process intensification strategy which enables adaptation of the microstructured photoreactor design (channel design, dimensions, light source, etc) to photochemical reaction specificities, and more generally a transfer from batch to continuous
mode operations.

Firstly, the principles and the interests of preparative photochemistry will be reminded as well as the conventional photochemical technologies. The common limitations encountered at industrial scale will be also identified and a general overview on flow photochemistry equipment presented. The main challenges linked to photochemical (micro)reactor engineering will then be exposed. By considering only the case of purely direct photochemical reactions A→B occurring in homogenous medium, the key factors to consider when implementing such a photochemical reaction in microstructured technologies will be outlined basing on modeling considerations. At last, some examples will be presented to illustrate, for this particular case of a photochemical reaction, how a chemical engineering framework enables to understand and formalize the positive effect of microstructured technologies for photochemistry.

Références

[1] N. Hoffmann, Photochemical Reactions as Key Steps in Organic Synthesis, Chem. Rev. 2008 108 1052­1103.
[2] N. Hoffmann, Photochemical reactions of aromatic compounds and the concept of the photon as a traceless reactant. Photochem, Photobiol. Sci. 2012 11 1613­1641.

[3] K. F. Jensen, B., J. Reizman, S. G. Newman, Tools for chemical synthesis in microsystems, Lab Chip 2014 14 3206–3212.
[4] E.E Coyle, M. Oelgemöller, Micro­photochemistry: photochemistry in microstructured reactors. The new photochemistry of the future? Photochem. Photobiol. Sci. 2008 7 1313­ 1322.

[5] M. Oelgemöller, O. Shvydkiv O., Recent Advances in Microflow Photochemistry, Molecules 2011 16 7522­7550.
[6] Y. Su, N.J.W. Straathof, V. Hessel, T. Noël, Photochemical Transformations Accelerated in Continuous­Flow Reactors: Basic Concepts and Applications, Chem. Eur. J. 2014 20 34 10562­10589.

[7] Loubière K., Oelgemöller M., Aillet T., Dechy­Cabaret O., Prat L., Continuous­flow photochemistry : a need for chemical engineering, Chem.Eng. Proc. 2016 104 120­132