Mieke Dams

23-O-02 - Pd-zeolites as catalysts for the Heck reaction: a screening of reaction parameters affecting catalyst heterogeneity

Publisher Summary This chapter discusses palladium (Pd)-zeolites as catalysts for the Heck reaction. It describes the screening of reaction parameters affecting catalyst heterogeneity. Heck reactions are performed with 4-bromoacetophenone and n-butyl acrylate, yielding the trans-substituted acrylate ester with high selectivity. Pd–mordenite is used as catalyst. The heterogeneous nature of the catalysis largely depends on the solvent used and on the base. With tributylamine as the base and in toluene, the Pd (0)–mordenite catalyzed Heck olefination is truly heterogeneous. The heterogeneous catalyst is less air-sensitive than typical homogeneous palladium catalysts that contain phosphine ligands.

New perspectives for zeolites in fine chemical synthesis

Zeolites can be used as heterogenous catalysts in the production of fine chemicals, as illustrated in the following reactions. With TS-1 and hydrogen peroxide, furans are oxidized to flavor compounds. La-exchanged zeolites are, in combination with hydrogen peroxide, a source of singlet dioxygen. Pd-loaded zeolites are heterogenous Heck catalysts, at the condition that proper pretreatment and reaction conditions are selected. Finally, acid zeolitic racemization catalysts have been successfully combined with a lipase for dynamic kinetic resolution of secondary alcohols.

Impact of Pd-mordenite pretreatment on the heterogeneity of Heck catalysis

In Heck reactions with tributylamine as the base and in toluene, Pd(NH3)4(2+)-mordenite (0.4 wt% Pd) and Pd0-mordenite (0.4 and 4 wt% Pd) are not only active and selective, but also truly heterogeneous catalysts, while oxidized PdII species in an all-oxygen environment, i.e. ionic Pd2+ or PdO, are prone to leaching.