Efficient Purification of 2,6-Lutidine by Nonporous Adaptive Crystals of Pillararenes.

2,6-Lutidine ( 2,6-LT ) is a very important raw material in the chemical industry, but the impurities of 3-picoline ( 3-PC ) and 4-picoline ( 4-PC ) existing in 2,6-LT seriously affect its quality. Considering different molecular sizes of these three compounds, herein, we exploit nonporous adaptive crystals (NACs) of pillararenes as purifying agents for removal of 3-PC and 4-PC in 2,6-LT . We find that per -ethylated pillar[5]arene ( EtP5 ) can selectively adsorb 3-PC and 4-PC , while negligible capture of 2,6-LT is observed, resulting in improvement of the purity of 2,6-LT up to 94.9%. Single-crystal structures indicate that the excellent selectivity originates from the size match and complexation stability differences among different host/guest pairs. After purification, NACs of EtP5 can be easily regenerated and used in the next run without a significant performance degradation.