IR Spectra and Component Ratios in SiO2–TiO2Organic Acid Composites―New Catalysts for the Asymmetric Biginelli Reaction

The amount of acid retained in the SiO 2 –TiO 2 *organic acid composites obtained by the sol-gel method depends on the structure of the acid and its concentration, but largely on the oxide ratio. At an acid concentration in the composite of less than 25%, its molecules undergo chemisorption accompanied by a change in the principal absorption bands in the IR spectra; as the acid concentration increases, physical sorption becomes prevalent. With acid-imprinted composites, an increase in the ee values in the asymmetric Biginelli reaction is observed, and the best results were obtained for aromatic acid-imprinted composites with an oxide ratio of 1 : 1.