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

Abstract

2,6-Lutidine (<b>2,6-LT</b>) is a very important raw material in the chemical industry, but the impurities of 3-picoline (<b>3-PC</b>) and 4-picoline (<b>4-PC</b>) existing in <b>2,6-LT</b> 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 <b>3-PC</b> and <b>4-PC</b> in <b>2,6-LT</b>. We find that <i>per</i>-ethylated pillar[5]arene (<b>EtP5</b>) can selectively adsorb <b>3-PC</b> and <b>4-PC</b>, while negligible capture of <b>2,6-LT</b> is observed, resulting in improvement of the purity of <b>2,6-LT</b> 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 <b>EtP5</b> can be easily regenerated and used in the next run without a significant performance degradation.