Catalytic investigation of(1R,2S)-(-)-N-dodecyl-N-methylephedrinium bromide immobilized on montmorillonite in the enantioselective alkylation of benzaldehyde with diethylzinc

摘要

The optically active cationic surfactant(1R,2S)-(-)-N-dodecyl-N-methylephedrinium bromide(DMEB)was immobilized on montmorillonite(M)via cation exchange.XRD studies revealed that the resulting hydrophobic clay organocomplex dodecylmethylephedri-nium-montmorillonite(DME-M)underwent a pronounced swelling in ethanol,tetrahydrofuran and toluene.The catalytic behaviour of the heterogenized surfactant was investigated for the enantioselective addition of diethylzinc to benzaldehyde and the results were compared with those obtained for DMEB in a homogeneous reaction,under otherwise the same conditions.The utilization of both DMEB and DME-M afforded pronounced selectivities for the formation of 1-phenyl-1-propanol.The application of DME-M was found to result in higher conversions and lower enantioselectivities than those observed for DMEB.The effect of the reaction temperature on the catalytic behaviour of the pristine and immobilized chiral surfactant was also examined.