Selective Separation of Methylfuran and Dimethylfuran by Nonporous Adaptive Crystals of Pillararenes.

The separation of 2-methylfuran (MeF) and 2,5-dimethylfuran (DMeF) mixtures is very important in the chemical industry. Herein, we offer a novel strategy for the separation of MeF and DMeF using nonporous adaptive crystals (NACs) of perethylated pillar[5]arene (EtP5), perethylated pillar[6]arene (EtP6), perbromoethylated pillar[5]arene (BrP5), and perbromoethylated pillar[6]arene (BrP6). We find that the crystals of EtP6 and BrP5 show remarkable selectivities for MeF in a 50:50 (v/v) MeF:DMeF mixture vapor, yielding purities of 94.0 and 96.3%, respectively. Single-crystal structures reveal that these different selectivities come from the different thermodynamic stabilities and binding modes of the host-guest complexes. Cycling experiments demonstrate that these crystals can be reused more than five cycles without loss of performance.