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.