P. Moreau

Selective isopropylation of naphthalene over zeolites

The isopropylation of naphthalene with isopropylbromide over a series of H mordenites and Y zeolites has been studied. In both cases, a high β-selectivity is observed in the monoalkylation and dialkylation reactions (selective formation of 2-isopropylnaphthalene and a mixture of 2,6- and 2,7-iisopropylnaphthalenes, respectively). Over H mordenites, the β-selectivity is explained as the result of transition-state shape selectivity. Over Y zeolites, the β-selectivity is due to a thermodynamic equilibrium favorable to the formation of 2-isopropylnaphthalene from 1-isopropylnaphthalene. The use of zeolites modified by silanation using chemical vapor deposition leads to an improvement of the β-selectivity by reducing the amount of trialkyl derivatives that are formed on the external surface.

Thioether oxidation by hydrogen peroxide using titanium-containing zeolites as catalysts

Abstract Titanium substituted ZSM-5 (TS-1) and BEA (Ti-beta) are investigated as catalysts for the selective oxidation of thioethers with diluted H2O2, in a protic solvent, at 303 K. The performances of TS-1 and Ti-beta samples are analyzed in relation with structure of thioethers, nature of solvent and shape selectivity effect of catalysts. A mechanism for organic sulfides oxidation on Ti-containing zeolites is proposed.

Factors affecting the efficiency of hybrid chiral mesoporous silicas used as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

Abstract Chiral hybrid organic–inorganic materials were prepared by anchoring optically active β-aminoalcohols such as (−)-ephedrine on MCM-41 type silica as a member of micelle-templated silicas (MTS). Silylation of the surface was performed with halogenopropyltrimethoxysilane. Then, (−)-ephedrine was anchored through halogen substitution. These materials were used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc. This work deals with the study of the various factors such as accessibility to the catalytic sites and coverage of the inorganic surface, which affect their efficiency (activity, selectivity and enantioselectivity).

The Solvent Effect in the Sulfoxidation of Thioethers by Hydrogen Peroxide Using Ti-Containing Zeolites as Catalysts

Abstract The oxidation reaction of ethyl sulfide by hydrogen peroxide is investigated in various organic solvents, without catalyst and over Ti-containing zeolites (TS-1 and Ti-beta, respectively) as catalysts. It is shown that the reaction rate greatly depends on the nature of the solvent (protic or aprotic) whether the reaction is catalyzed or not. In the case of the catalyzed reaction, Ti-beta is more active and selective than TS-1 for all the solvents.

Chiral mesoporous templated silicas as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

Abstract New mesoporous templated silicas of the MCM-41 family covalently linked to chiral ephedrine are used as heterogeneous chiral auxiliaries in the enantioselective alkylation of benzaldehyde by diethylzinc. Promising results are obtained with these inorganic–organic catalysts. Various factors which may affect the activity, selectivity and enantioselectivity are studied. Comparison with homogeneous catalysis is carried out.

Oxidation of sulfoxides to sulfones by hydrogen peroxide over Ti-containing zeolites

The oxidation reaction of dibutylsulfoxide to the corresponding sulfone by dilute hydrogen peroxide is investigated over Ti-containing zeolites as catalysts; Ti-beta is more active than TS-1, as for the oxidation of sulfides under similar conditions. The kinetic parameters are determined over Ti-beta in t-butanol as solvent, and the kinetic law of the sulfoxide oxidation reaction is established. The influence of the reaction temperature and effect of the solvent are also reported.

Catalytic enantioselective addition of diethylzinc to benzaldehyde induced by immobilized ephedrine: comparison of silica and MCM-41 type mesoporous silicates as supports

The synthesis and characterization of a chiral amino-alcohol ((1R-2S)-ephedrine) immobilized on MCM-41 type mesoporous silicas (MTS: Micelle Template Silicas) are described. The activity of these supported catalysts in the enantioselective addition of diethylzinc to benzaldehyde are reported, and compared with those obtained with the corresponding silica gel supported catalysts. The observed differences are discussed in terms of the nature of the grafting which depends on the support structure.

Rearrangement of Epoxides Using Modified Zeolites

Summary The rearrangement of styrene oxide into phenylacetaldehyde was studied over various zeolites (H-ZSM-5, HY, H-offretite). It was first shown that both external and internal acidic sites are involved in that easy isomerization. Moreover, a comparative study of the rearrangement of this epoxide and of its hindered analog, l-phenyl-1,2-epoxycyclohexene, on silanated offretite, allowed a discrimination between the activities of these sites.

Selective sulfoxidation of thioethers on Ti-containing zeolites under mild conditions

The oxidation of various thioethers with aqueous H 2 O 2 in organic solvents, over two titanium containing zeolites, TS-1 and Ti-beta has been studied. The performances of these catalysts depend strongly on the thioether structure and the nature of solvent. Thus, the reactivity of organic substrates is in agreement with the nucleophilic character of the sulfur atom and their molecular size: (Ethyl) 2 S>(Propyl) 2 S>(Allyl) 2 S>(Butyl) 2 S>Methyl-S-Phenyl>(Phenyl) 2 S. The conversion of sulfide in protic solvents is higher than that obtained. in aprotic solvents. For all the solvents, Ti-beta is more active and selective than TS-1 in the oxidation of hindered molecules.

Selective Synthesis of Carbonyl Compounds Using Zeolites

Various typical acid-catalyzed reactions leading to carbonyl compounds were studied using zeolites taking into account their acidic and shape selective properties. Acylation of aromatic compounds by carboxylic acids over Y zeolites leads to quantitative conversion in acylated derivatives with very high para selectivity. On the other hand, the Fries rearrangement of phenylbenzoate gives mainly ortho hydroxybenzophenone. Zeolites are also efficient catalysts in hydration of various aromatic and aliphatic alkynes leading to the corresponding ketones. The epoxide rearrangement of styrene oxide yields phenylacetaldehyde with high conversion. In this latter case, the use of surface-modified zeolites shows that both external and internal acid sites of the zeolite are involved in liquid phase epoxide conversion.