A comparison of various cross‐linked polystyrenes as diluting media in reactions of ester enolates

Abstract

AbstractVarious forms of cross‐linked polystyrene were compared as to their effectiveness as carriers‐diluents in reactions of carboxylic ester enolates. The polymers compared were microporous (2 % divinylbenzene), “popcorn,” and macroporous polystyrenes. In the acylation by acyl halides of polymer ester enolates, higher yields were obtained and less self‐condensation occured with the popcorn polymer as carrier than with the microporous polystyrene. Popcorn and microporous polymers gave similar results in the alkylation of polymer ester enolates. The macroporous polymers (both commercial and synthetized) gave much poorer results in this latter reaction (low yields and more self‐condensation). Popcorn and microporous polystyrenes gave equally good results in the mixed ester condensation of two esters attached to a common polymer backbone. When polymer esters were treated with base without subsequent addition of electrophile, 10‐15% of intrapolymeric self‐condensation occurred with all three types of polymer, when ester concentration was 0.1‐0.15 mmole/ g. Under similar conditions, the analogous soluble ester self‐condensed to the extent of 67 %. It is concluded that under the proper conditions, all of the cross‐linked polystyrenes are capable of inhibiting mutual interactions of attached molecules. These conditions are low concentration and low molecular weight of attached molecules, and short reaction times.