Hydroformylation

Résumé

vignette|upright 2.5|Hydroformylation. L'hydroformylation, appelé aussi procédé oxo, est une voie de synthèse pour produire des aldéhydes à partir d'alcènes découverte en 1938 par Otto Roelen de chez Ruhrchemie. La réaction de base est celle du schéma ci-contre. Ce procédé est principalement utilisé pour produire des aldéhydes dans un intervalle de C3-C19. Le butanal est d'ailleurs le principal produit synthétisé par cette réaction avec environ 75 % de la production totale utilisant l'hydroformylation comme voie de synthèse. À l'origine, des catalyseurs à base de cobalt étaient utilisés pour améliorer le rendement. Toutefois, à partir des années 1970, des catalyseurs à base de rhodium sont introduits pour répondre notamment au choc pétrolier : en effet, si les catalyseurs à base de rhodium sont plus chers, ils améliorent sensiblement la conversion à une époque où le coût principal de la production provient des réactifs. Les catalyseurs en rhodium ont une meilleure sélectivité pour l

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https://fr.wikipedia.org/wiki/Hydroformylation

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Accessing and predicting the kinetic profiles of homogeneous catalysts from volcano plots

Michael Markus Busch, Matthew Wodrich

Volcano plots are frequently used as aids in the search for new heterogeneous and electrochemical catalysts. These tools successfully predict catalytic processes based solely on thermodynamic descriptions, which also capably describe many aspects of the catalytic cycles of homogeneous species. However, homogeneous catalysts also frequently depend upon the kinetic influences brought about by steric interactions to promote or prevent specific chemical reactions. Here, a prototypical transformation facilitated by a homogeneous catalysis, the hydroformylation of an olefin using CO and H2, is examined to establish the viability of creating kinetic volcano plots and to determine their ability to ascertain the influences steric bulk plays on catalytic cycle energetics. Similar to their thermodynamic counterparts, kinetic volcanoes successfully reproduce many experimentally known facets of the hydroformylation reaction. In contrast to thermodynamic volcanoes, kinetic volcanoes emphasize changes in the height of the different activation barriers brought about by steric interactions. This crucial information, however, comes with considerable computational cost, since the transition states of catalysts bearing large bulky ligands must be identified and characterized. To overcome this drawback, a procedure is proposed that relates a simple steric parameter, the Tolman cone angle, with the descriptors used to create the kinetic volcano plots. In this way, the activation barriers of bulky catalysts can be estimated without requiring expensive transition state computations. These newly derived structure-activity relationship volcano plots represent useful tools for identifying new homogeneous catalysts.

Royal Soc Chemistry2016

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The discovery of new homogeneous catalysts that preferentially form one product over another in regio- or enantioselective chemical reactions has traditionally been the province of experimental chemists. Today, computational-based approaches have carved an increasingly important role, which, for computational catalytic designs, often rely on highly inefficient combinatorial-based screening methods. To increase the pace of discovery, tools capable of rapidly assessing large numbers of prospective species and identify those possessing desirable properties, such as activity and selectivity, are vital. Here, through the examination of the hydroformylation of 2-methylpropene, we demonstrate how a new tool built upon molecular volcano plots can be used to quickly predict the activity of molecular catalysts as well as estimate the intrinsic ability of each species to form one regioisomer over the other with striking accuracy. Following training and validation, these regioselective molecular volcanoes are employed to predict catalysts that preferentially form the branched product (2,2-dimethylpropanal) in violation of Keulemans' 70-year-old law. Eighteen species (out of a total of 68 predicted) were computationally predicted to have regiomeric excess (r.e.) values >90. Overall, these tools can be used to quickly screen the activity and selectivity of potential catalysis based on two easily computed descriptor variables.

WILEY-V C H VERLAG GMBH2018

Chargement

Different micellar systems are characterized. Hydroformylation reactions are carried out in the most appropriate ones and are compared with hydroformylations in a non-micellar system. Reaction rates and selectivities for aldehydes are higher than the micelles. In addn. to this, olefins between C6 and C16 are successfully hydroformylated in the micellar system, whereas C8 is the highest olefin that can be hydroformylated without micelles. The behavior of the reaction in the micellar system is very sensitive to the initial compn. and reaction conditions. [on SciFinder (R)]

1999

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