Hydrogen Transfer Reduction of 4-tert-Butylcyclohexanone and Aldol Condensation of Benzaldehyde with Acetophenone on Basic Solids

The liquid-phase reduction of 4-tert-butylcyclohexanone into 4-tert-butylcyclohexanol by reaction with isopropanol at 355 K has been studied on solid bases: mixed oxides obtained by calcination of hydrotalcites, NaBEA zeolites, KF/alumina, and La2O3 characterized by calorimetric FTIR adsorption of CO2 and FTIR pyridine adsorption. The aldol condensation of benzaldehyde and acetophenone at 423 K was investigated in parallel to clarify the mechanism of deactivation. For hydrogen transfer, the addition of amine to the reaction medium had only a small effect, but benzoic acid strongly decreased the rate, suggesting catalysis by basic sites. Hydrotalcite was also active and selective for the hydrogenation of cinnamaldehyde into cinnamylalcohol. The stronger bases such as KF/alumina and La2O3 showed a low activity for hydrogen transfer, due to deactivation by the products of the parallel aldolization of the ketone. The exchange of BEA by Na+ increased the selectivity to cis-alcohol with little effect on activity. NaBEA zeolites retained extraframework Al species of strong Lewis acidity and catalyzed the reduction of cinnamaldehyde into isopropyl-cinnamyl ether, thus suggesting an acidic mechanism in that case.