Polystyrene-supported ammonium fluoride as a catalyst for several base-catalyzed reactions

Lightly crosslinked polystyrenes with ammonium chlorides were ion-exchanged to a fluoride form. The fluoride polymers functioned as good catalysts for several base-catalyzed reactions, such as cyanoethylation, Knoevenagel reaction, Claisen condensation and Michael addition. Their catalytic activity was comparable to that of tetrabutylammonium fluoride (TBAF). The factors controlling the catalytic efficiency for the reaction between ethyl acetoacetate and benzaldehyde were examined in detail. Ionic loading and ammonio structure of the fluoride polymers hardly affected the catalytic efficiency. The reaction was fast in a non-polar solvent, such as octane or toluene. The solvent effect was very similar to that of nucleophilic substitution reactions. These results suggest that the rate-determining step of the base-catalyzed reaction is not the formation of a conjugate base from the reagent acid, but the attack of the nucleophilic anion on electrophiles.