Photochimie fine dans des milieux complexes

Abstract : For industrial chemistry and especially for fine chemistry, photochemistry is a powerful synthetic tool. Light (photons) represents a highly specific reagent, offering new synthetic pathways, more selective and less aggressive than thermal ones. ln order to set up a new process in an optimal way and particularly to favor a target product, the photochemist bas to weIl know the absorption properties of the irradiated substances, their excited states and to analyze accurately their different deactivation pathways ; aIl these characteristics depend not only on the structure of the compounds but also on their environment (solvent nature, order of the medium, polarity, viscosity, etc.). With these ideas in mind, photochemistry was developed in complex media, which modify the environment features by comparison to classical solvents : (i) organized molecular systems (OMS), which undergo a higher local order at molecular level and a different and local concentration distribution for products, (ii) supercritical fluids (SCF), which have low viscosity and high diffusivity properties. The involved photoreactions concern the production of high value products : previtamins D, retroketal, cis-jasmone. For these compounds, one of the photoreactivity key steps consists of a cis/trans isomerization, which is particularly sensitive to the environment properties.Provitamins D irradiation (ergosterol, proketal) in OMS improve the previtamins production (precursors of vitamins D and retroketal) by lowering the cis/trans isomerization rate (PVD/tachysterol). The SCF use (carbon dioxide) which increases the trans/cis isomerization efficiency of jasmone would valorize the trans-jasmone isomer
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http://docnum.univ-lorraine.fr/prive/INPL_T_1995_NAOUMI_S.pdf
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Submitted on : Thursday, March 29, 2018 - 1:23:49 PM
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Said Naoumi. Photochimie fine dans des milieux complexes. Autre. Institut National Polytechnique de Lorraine, 1995. Français. ⟨NNT : 1995INPL129N⟩. ⟨tel-01751653⟩

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