Isolation of cucurbit[n]uril homologues with imidazolium salts in a recyclable manner

Abstract

A method for isolating cucurbit[n]uril (CB[n]) homologues (CB[5–8]) has been developed by utilising several selective imidazolium salts. Complexation with CB[7] and CB[8] causes a dramatic increase in their solubility in water, allowing for facile separation of CB[5] and CB[6] from their corresponding mixtures. The larger homologues (CB[7] and CB[8]) can then be isolated as pure, uncomplexed macrocycles via a solid state metathesis (SSM) ion exchange reaction. Moreover, the imidazolium salts can be readily recycled after CB[n] purification, leading to a near-quantitative recovery loop and providing a “green” isolation process. This methodology remarkably increases the isolated yields of each of the major CB[n] components, reduces the time required for purification, and is amenable to scale-up, which would represent a significant improvement in the field of macrocycles.