Polymeric Lewis acid catalysts

The synthesis and utility of polymer-bound Lewis acid catalysts were studied. The polymers, poly(p-methoxystyrene) and its copolymers with styrene and divinylbenzene, poly(phenyl vinyl ether), poly(p- cresyl vinyl ether), poly(2,6-xylyl vinyl ether) and poly(methyl vinyl ether), were evaluated as substrates for boron trifluoride. The adducts formed were used to catalyze esterification and olefin isomerization.

Poly(p-methoxystyrene) was made by the suspension polymerization of the monomer which was prepared from p-anisaldehyde using the Wittig reaction. Poly(aryl vinyl ethers) were made by the carbocationic polymerization of the monomers made by dehydrohalogenation of the β-bromophenetoles. The β-bromophenetoles were prepared from the phenols using the Williamson synthesis. The adducts were made by allowing the polymer solutions or swollen polymer in methylene chloride to absorb boron trifluoride at –72°C under reduced pressure.

The polymeric catalysts effectively catalysed the esterification of propionic acid with both ethanol and n-butanol and the isomerization of 1-octene to 2-octene. Catalytic activity was inversely parallel to both the proximity of the active site to the polymer backbone and the degree of crosslinking in the polymer, and independent of molecular weight. The catalyst induced a minor (undefined) rearrangement of the substrates which limited recyclability of the adducts.