Some novel aspects of cationic ion-exchange resins as catalysts

Cationic ion-exchange resins, particularly the macroporous variety, are versatile catalysts which offer several advantages over the homogeneous acid catalysts with respect to corrosion, product recovery, selectivity, etc. In some cases, such as etherification of phenols/naphthols with isobutylene/isoamylene, resin catalysts allow the reaction to occur, but the homogeneous catalysts fail. A noteworthy development has been the use of distillation column reactors (DCR) where the exothermicity of the reaction is usefully employed and the resin inventory, for a specified level of conversion and productivity, can be significantly reduced. The availability of methyl-tert-butyl ether and tert-amyl methyl ether allows tert-butyl and tert-amyl derivatives of phenolic substances to be produced with the attendant advantages. The removal of low concentrations of substances like formaldehyde in aqueous medium offers new opportunities for resin catalysts and methylal formation with methanol in DCR has been realized in bringing down formaldehyde concentration from 1 to 2% (wt) to as low as 0.02%. Resin catalysts are useful for oligomerization of olefins like isobutylene, isoamylene, alpha-methyl styrene, etc.; cross-dimerization of olefins for making precursors for synthetic musks, can also be advantageously carried out. The alkylation of dissolved polyvinyl phenol with isobutylene, with resin catalysts is interesting in several ways. Many close-boiling substances, such as isomeric and non-isomeric phenolic substances, can be separated through selective reactions based on resin catalysts.