Pierre Laszlo

Chemical reactions on clays.

Layer aluminosilicates catalyze reactions in numerous ways. They stabilize high-energy intermediates. They can store energy in their lattice structures and can release it in the form of chemical energy. They can catalyze redox reactions and can serve as photocatalytic devices. They often exhibit high surface acidity. Organic reactions that are catalyzed by the agency of days are reviewed. The role of clays in prebiotic chemistry is also examined.

Catalysis of the Diels-Alder reaction in the presence of clays

Fe III- doped K10 montmorillonite combined with 4-t-butylphenol (10 mol %) is a potent catalytic system for unactivated dienophiles.

Easy formation of diels-alder cycloadducts between furans and α,β-unsaturated aldehydes and ketones at normal pressure.

The K-10 bentonite clay doped with FeIII or, even better AlCl3 alone catalyse the Diels-Alder reaction between furan or dimethyl-2,5-furan and either acrolein or methyl- vinylketone. The cycloadducts are obtained with isolated yields in the range 20–81%.

Acceleration of the diels-alder reaction by clays suspended in organic solvents

Abstract Rapid and stereoselective Diels-Alder reactions can be run in ethanol or methylene chloride in the presence of Fe III - doped K10 montmorillonite.

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.

Catalysis of the knoevenagel condensation

Xonotlite alone or made more basic by doping of potassium t-butoxide catalyses the title reaction between aromatic aldehydes and malononitrile or alkyl cyanoacetates. At ambient temperatures, this procedure specifically gives high yields of E olefinic Knoevenagel products.

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.

Catalysis of the specific michael addition : The example of acrylate acceptors

Abstract Lewis acids, ferric chloride in particular, catalyze the addition of amine nucleophiles to acrylates. Yields are very good, under mild conditions. Exclusive 1,4-addition occurs, and polymerization is avoided.

Product distribution in diels-alder addition of n-benzylidene aniline and enol ethers

Abstract The two diastereomeric products, all cis , and trans phenyl, form in highly variable ratio (up to a factor 20), depending on the conditions.

Dual catalysis of the michael reaction

Abstract The Michael reaction, with conjugate bases of β-diketones as donors and with α,β-unsaturated ketones as acceptors, is efficiently catalyzed by a combination of clay-supported nickel bromide (heterogeneous) and ferric chloride (homogeneous).