Synthesis and Spectroscopic Study of Si, Ti, Mg, and Zn Oxides Modified by L-Proline

Individual and mixed oxides of Zn, Mg, Si, and Ti modified with L-proline during their solgel synthesis have been obtained. The IR spectra of these oxides studied in detail show changes in the vibrational band parameters of the siliconoxygen and metal–oxygen bonds. Enhancement of the amount of basic sites on the SiO 2 –TiO 2 mixed oxide was found after removal of L-proline from the surface. The use of SiO 2 –Mg(OH) 2 * L-proline composite as a catalyst leads to an enhanced enantiomeric excess of some asymmetric Biginelli reaction products up to 18%.