Sándor Békássy

Benzylation of aromatics on ion-exchanged clays

The alkylation of benzene and toluene with benzyl chloride and benzyl alcohol have been investigated over a series of clays obtained by exchanging the original cations of K10 by Ti4+, Fe3+, Zr4+, Cu2+, Zn2+, Ce3+, Cr3+ and Sn2+ cations. The acidity of these solids has been determined by infra red spectrometry using pyridine as molecular probe. The acidity of K10 clays can be changed to a great extent by cation exchange and by the thermal treatments applied to the solids. The clays treated in air at 773 K show practically pure Lewis acidity, while those dried at 393 K possess Bronsted acidity. The rate of alkylation is roughly related to acidity when the substrate is benzyl alcohol, but not when benzyl chloride is used. In that case the catalysts containing reducible cations (Fe3+, Sn4+, Cu2+) exhibit high activities in spite of their low number of acid sites. It is proposed that an oxido-reduction is the first step of the reaction in that case.

Characterization of clay-based K catalysts and their application in Friedel-Crafts alkylation of aromatics

Abstract Toluene was alkylated with benzyl chloride and benzyl alcohol using a series of clays (KSF, KSF/0, K0, KP10, K10, KS from Sud Chemie) obtained by treating a bavarian bentonite by different acids and a Hungarian bentonite (Mad) as catalysts in a batch reactor. The catalysts were characterized by chemical analysis, thermal analysis, nitrogen adsorption, solid state nuclear magnetic resonance, X-ray diffraction. The acidity of these solids was determined by infrared spectroscopy using pyridine as molecular probe. The structure, specific surface area, and distribution of Lewis/Bronsted acidity of these clays can be changed to a great extent by acidic or thermal treatment. The rate of alkylation is related to Bronsted acidity when the substrate is benzy alcohol. When benzyl chloride is used as alkylating agent, the Fe3+ content of the clay controls the activity, and iron containing clays show high activities in spite of their low Lewis acidities.

Heterogeneous catalysis for the acetylation of benzo crown ethers

Abstract Heterogeneous catalytic acetylation of benzo-15-crown-5 was investigated using solid Lewis acids consisting of sulfated zirconia calcined at 625°C or K10 exchanged by Cu, Zn, Fe or Sn ions and treated at 250°C. The nature of the transition metal ions introduced in the mesoporous clay plays an important role in the activity of the catalysts. Sn-exchanged K10 shows the best catalytic properties and could suit for practical preparative purposes. 4′-Acetyl-benzo-15-crown-5 was produced with 90% yield under optimal conditions.

Acylation of Resorcinol on Clay Catalysts

Abstract Using a series of clay based catalysts (KSF, KSF/0, KP10, K10, K0, KS), resorcinol is acylated in 1,2-dichloroethane by phenylacetyl chloride with a heterogeneous catalytic procedure. The yield of 1-(2,4-dihydroxyphenyl)-2-phenyl-ethanone is in correlation with the specific surface area of the catalyst.

Catalytic decomposition of 1,4-diisopropylbenzene dihydroperoxide on montmorillonite-type catalysts

Abstract A series of montmorillonite-based clays as acid character catalysts (KSF, KSF/0, K0, KP10, K10, KS from Sud Chemie) and their ion-exchanged derivatives with Zn2+, Mg2+, Cu2+, Al3+, Fe3+, Sn2+ were used in the decomposition process of the dihydroperoxide of 1,4-diisopropylbenzene whose conversion is of industrial relevance. The influence of the specific surface area and the acidity of the catalysts on the decomposition rate were investigated. The best catalytic activities were obtained with KS and Sn2+-K10 catalyst. In the case of Fe3+ as reducible cation the advantageous effect of O2 from air supported the possibility of a redox character of the reaction mechanism.

Selectivity of C- Versus O-acylation of diphenols by clay catalysts. I. Acylation of resorcinol with phenylacetyl chloride

Resorcinol was acylated by phenylacetyl chloride with a set of catalysts consisting of the montmorillonite-based K-series and their cation-exchanged forms. The selectivity of C-acylation over O-acylation could be significantly increased by an appropriate ion exchange and by a solvent-free reaction mode, resulting in a 60% preparative yield of 1-(2,4-dihydroxyphenyl)-2-phenyl-ethanone.

Modified clay catalysts for acylation of crown compounds

Summary Heterogeneous catalytic acetylation of benzo-15-crown-5 was investigated using different ion exchanged K10 catalysts. The nature of the transition metal ions introduced in the mesoporous clay plays an important role in the activity of the catalysts. Fe3+-K10 is particularly advantageous for practical preparative purposes. 4′-Acetyl-benzo-15-crown-5 was isolated with 55% yield under optimal conditions.

ACETYLATION OF B15C5 CROWN ETHER ON CU MODIFIED CLAY CATALYSTS

Abstract With different copper-clay based catalysts, in the presence of AcCl as acetylation agent, B15C5 crown ether is acetylated in a convenient heterogeneous catalytic procedure. We show here the first heterogeneous catalytic method for crown ether acylation, where the Cu exchanged clay gives the best results using really catalytic amount of catalyst.

Heterogeneous Catalytic Acylation of Benzo Crown Ether Using Acetic Anhydride

Abstract Benzo-15-crown-5 macrocycle has been acetylated using acetic anhydride and a series of cation exchanged clays. This acetylating method has great advantages such as the significant reduction of the formation of by-products, lower price and the possibility of environmental friendly process. Yields as high as 80% for the acetylated compound are reached in short times.

Partial dealcoholization of red wine by nanofiltration and its effect on anthocyanin and resveratrol levels

The present work studies the use of nanofiltration for the production of red wine concentrate with low alcohol content. Factorial design was applied to measure the influences of transmembrane pressure (10–20 bar) and temperature (20–40 ℃) on the retention of valuable components such as anthocyanins and resveratrol, and on the nanofiltration membrane performance. The highest retention of anthocyanin and resveratrol was achieved at low temperature (20 ℃), while the high transmembrane pressure (20 bar) was found to increase the permeate flux considerably. The experiments demonstrated that nanofiltration appears as a valid technique for the production of low alcohol content red wine concentrate. Reduction of volume by a factor of 4, leads to 2.5–3 times more anthocyanins and resveratrol in the wine concentrates. The final new wine products – obtained by using various forms of reconstitution of the concentrated wine – had low alcohol content (4–6 % by volume) and their sensory attributes were similar to those of the original wine.