Michel Spagnol

Kinetic study and reaction mechanism of the hydroxyalkylation of aromatic compounds over H-BEA zeolites

Hydroxyalkylation of various carbocyclic aromatic compounds has been carried out in the presence of dealurninated H-form BEA zeolites. A kinetic study has been realized by varying several reaction parameters such as catalyst weight, initial concentration in aromatic reactants, temperature, substituent effects on aromatic substrates. The experimental results obtained allowed to propose a ‘poisoned Eley–Rideal’ reaction mechanism, where the adsorbed aromatic substrate does not react with a molecule of chloral, but acts as a poison of the reaction. The ratio of the adsorption constants of the two reactants has been determined. Anisole was found to be more strongly adsorbed than chloral. Moreover, it has also been shown that this electrophilic aromatic substitution reaction follows a Hammett-type correlation, with a strong negative ρ-value of −4. The presence of a strong electron-donating substituent on the aromatic ring not only increases the reaction rate, but also favors the formation of the undesired bisarylalkanes.

Surface organometallic chemistry on metals: Influence of the presence of functional groups grafted at the surface of Rh particles on the competitive hydrogenation of terminal and internal double bonds of unsaturated primary alcohols

Abstract Careful hydrogenolysis of organometallic compounds with group VIII metallic surfaces lead to surface organometallic fragments directly grafted on the metallic particles with well-defined structures. The presence of such surface organometallic fragments was demonstrated by various physical and chemical techniques (EXAFS, magnetic measurements, IR spectroscopy, Mossbauer, thermoreduction, etc.). Surface organometallic complexes with an average formula M s [M′R x ] y (M: Rh, Pt, Ni; M′: Sn, Ge, Si, Se; R: Me, Et, Bu) were proposed. It was recently demonstrated that organometallic fragments with functional groups can also be grafted on a platinum or rhodium surface. In this work, we demonstrate that organo-tin fragments with functional groups, grafted on a silica-supported rhodium surface can strongly modify the regio-selectivity of the hydrogenation of unsaturated primary alcohols. The rate of hydrogenation of trans -2-hexenol and 5-hexenol was determined at room temperature under 20xa0bar of hydrogen in heptane solution for Rh/SiO 2 catalysts which were either used as they were or were modified with Bu 3 Sn(CH 2 ) 3 OH or Bu 2 Sn[(CH 2 ) 2 (O(CH 2 ) 2 ) 2 OMe] 2 . The rate of hydrogenation of the terminal double bond is slightly modified by the presence of functional groups, while that of the internal unsaturation decreases by a factor of 4. These results are explained by the formation of a hydrophilic layer around the metallic particle which inhibits the adsorption of the unsaturated alcohol by its internal double bond.

Synthesis and evaluation of poly-NAP-Ru, an heterogeneous enantioselective catalyst

Abstract An heterogeneous catalyst was synthesized by polymerization of a BINAP derivative followed by complexation with ruthenium. This catalyst showed high enantioselectivities for the hydrogenation of various substrates such as dehydroaminoacids, α-ketoesters, olefines, β-ketoesters and ketones. The catalyst may be re-used four times with negligible loss of enantioselectivity and activity.