Amine-Catalyzed Reactions Enhanced by Acid Site on Silica-Alumina

Amine-Catalyzed Reactions Enhanced by Acid Site on Silica-Alumina 

Owing to the weak acidity of the silanol groups, the coexistence of organic amines and silanols is very easy. However, their restricted appHcation to limited examples of organic reactions is one of the problems of the amine-silanol paring system. To solve this problem, we investigated the use of siHca-alumina as a more acidic support compared with sihca for the preparation of acid-base bifunctional catalysts [13]. 

The signals of the mixtures of SA and triethylamine appeared at higher fields than of SA-NEt2. For example, a peak of triethylamine adsorbed on the SA surface showed the largest upfield shift (11.8 (triethylamine in CDClj solution) to 7.5 ppm). These results indicate that the add-base interaction between the tertiary amine and the add site on sihca-alumina becomes weak by silane ouphng immobilization. 

The Michael reaction of nitriles with unsaturated carbonyl compounds was examined using the SA-NEtj catalyst As shown in Table 1.6, the SA-NEtj showed the highest catalytic activity for the Michael reaction of ethyl 2-cyanopropionate with ethyl acrylate to afibrd 2-cyano-2-methyl glutaric acid diethyl ester in 94% yield (entry 1). SiOj-NEtj was much less active under the reaction conditions (entry 2). Neither triethylamine nor sihca-alumina promoted the desired addition reaction (entries 3 and 4). Notably, the reaction scarcely proceeded with the 

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