Optimizing host–guest selectivity through side-chain modification of pillar[6]arenes for o-ethyltoluene/m-ethyltoluene separation

Separation of o-ethyltoluene (OET) and m-ethyltoluene (MET) poses a significant challenge in industrial applications due to their closely matched boiling points and similar chemical structures. In this study, we successfully achieve selective adsorptive separation of OET over MET by tuning the host–guest interactions of pillar[6]arenes with ethyltoluene isomers. Experimental results demonstrate that activated perbromoethylated pillar[6]arene (BrP6) can effectively separate OET and MET, yielding an impressive OET purity of 94.0 %. Unlike conventional alkyl chain-modified pillar[6]arenes such as perethylated pillar[6]arene (EtP6) and n-perpropylated pillar[6]arene (PrP6), the improved selectivity of BrP6 arises from the electron-withdrawing effect induced by the bromine atoms present on the side chain. The presence of bromine atoms enhances the electropositivity of the side chain in BrP6, amplifies the contrast in electron cloud density between the branched chains and the cavity of BrP6, and further facilitates the favorable binding of OET with BrP6 due to the concentrated electron density in OET's branched chain.