Separation of toluene and alcohol azeotropes by nonporous adaptive crystals of pillar[n]arenes with analytical purity of 100%

The separation of azeotropic mixtures is a key process to achieve the production of high-purity chemicals and the recovery of high value-added products, which is common but difficult in various industrial fields. However, conventional separation strategies suffer from some problems. Here, we report an energy-efficient and environmentally friendly adsorptive separation method to separate toluene and alcohol azeotropes using nonporous adaptive crystals of perethylated pillar[5]arene (EtP5α) and pillar[6]arene (EtP6β). EtP5α or EtP6β separates toluene from a mixture of toluene and alcohol with analytical purity of 100%. Single crystal structures and theoretical calculations reveal that the analytically perfect selectivity originates from the thermodynamic stability of the new host-guest structure of EtP5α or EtP6β upon capturing the preferred guest molecule. The size matching between the toluene molecule and the cavity of pillar[n]arenes is also one of the reasons for the selective separation. Moreover, EtP5α and EtP6β exhibit excellent recyclability and stability.