Guanidines encapsulated in zeolite Y and anchored to MCM-41: synthesis andcatalytic activity

The preparation and characterisation of guanidines encapsulated in zeolite Y and anchored to MCM-41 are described. The catalytic activity of the immob ilised and free guanidines were tested in the aldol reaction of benzaldehyd e with acetone. In homogeneous phase, the guanidines give in 90-94% yield t he condensation product alone. When anchored to MCM-41, the total yields ra nge from 31% to 89% and the addition product is also formed depending on th e solvent used. However, for the guanidine encapsulated in zeolite Y, the r ate is strongly reduced and the addition product is preferentially formed i n only 48% yield after 6 days. The reduced activity of this catalyst is exp lained by diffusional restrictions of the reactants and products inside the microporous system. (C) 1999 Elsevier Science B.V. All rights reserved.