REACTION-MECHANISM AND FACTORS INFLUENCING PHASE-TRANSFER CATALYTIC ACTIVITY OF CROWN ETHERS BONDED TO A POLYSTYRENE MATRIX

Polymer-supported crown ethers were prepared by reaction of 1% cross-linked chloromethylated polystyrene, with (hydroxymethyl)- and ( omega -hydroxynonyl)-18-crown-6, respectively. Their phase-transfer catalytic activity was tested in anion-promoted nucleophilic aliphatic substitutions and compared with that of structurally similar soluble crown ethers and of polymer-supported and soluble phosphonium salts. Catalytic efficiency of crown ethers is found to depend on a combination of three parameters: the nature of the nucleophile, the percent ring substitution, and the presence of a spacer chain. Complexation of potassium salts largely depends on the anion, with a high degree for soft nucleophiles like I** minus and SCN** minus and a lower degree for smaller and less polarizable nucleophiles like Br** minus and CN** minus .