André Cornélis

Friedel−crafts acylations with modified clays as catalysts

Friedel-Crafts acylations are very effectively catalyzed by clays modified through exchange of the interlamellar cations or through impregnation of metal chlorides. The acidic K10 montmorillonite exchanged with iron(III) gives outstanding results in quantitative (98–100%) acylation of anisole (15 min), mesitylene (15 min), and p-xylene (3 h) at 140–160 °C. Clays impregnated with zinc chloride, such as the K10 montmorillonite, or Japanese acidic clay show near-equivalent catalytic performance.

Cleavage of thioacetals by clay-supported metal nitrates

Abstract Bis(methylseleno)acetals and bis(phenylseleno)acetals are cleaved into aldehydes or ketones, under very mild conditions, by K10 clay-supported ferric or cupric nitrate.

Clay-supported reagents IV. A novel coupling of thiols into disulphides, via thionitrite intermediates using a clay-supported nitrosation reagent.

Abstract Thiols are converted into symmetrical disulphides, under very mild conditions, by bentonite-supported Fe(NO 3 ) 3 .9 H 2 O.

Thiocarbonyls into carbonyls: efficient conversion by clay-supported ferric nitrate

Abstract A simple and inexpensive procedure is proposed for achieving the title transformation. The method works best with thiobenzophenones (60–100 % yields).

Synergistic acceleration of reactions having clay-based catalysts

Aromatic hydrocarbons are submitted to Friedel-Crafts alkylation in the presence of the K10 montmorillonite impregnated with zinc chloride. The presence of benzene is found to improve significantly competitive alkylation of a co-reactant.

Preparative Organic Chemistry Using Clays

Application of clays, modified clays or clay-supported reagents to chemistry is receiving increasing interest. This lecture will focus on recent applications to preparative organic chemistry designed and developed in our group: n nA.- n nMetallic nitrato complexes, with covalent metal-ligand bonds, stabilized by impregnation upon a clay, offer versatile applications to organic synthesis. As a source of NO+ nitrosonium cations, they perform a number of functional group interconversions. They effect also the regioselective mononitration of phenols. n n n n nB.- n nThe Diels-Alder reaction is catalysed by radical cations generated by phenols in the presence of clays or by the protic or the Lewis acidic sites of montmorillonites. Clay catalysts also achieve stereo-specificities comparable to those, of cycloadditions performed in aqueous media. n n n n nC.- n nSaturated hydrocarbons, in the presence of acidic clays, react with carbon tetrachloride or with aromatic hydrocarbons without prior activation. These reactions have been tested on adamantane as a probe substrate.

Fast Kinetics by NMR: Binding and Release of Cations by Biomolecules

Because of its high sensitivity, sodium-23 nuclear magnetic resonance (NMR) is useful for the study of ion-substrate interactions (1). Complex formation induces a relaxation enhancement of the nuclear spins manifested by line broadening whereas the position of the peak is little affected. Under some conditions, such relaxation measurements can be used to determine the forward and the reverse rate constants for complex formation. In this paper we present examples of the determination of kinetic parameters by NMR.