Separation of Monochlorotoluene Isomers by Nonporous Adaptive Crystals of Perethylated Pillar[5]arene and Pillar[6]arene

Separation
of monochlorotoluene isomers is a vital process to obtain
highly pure p-chlorotoluene, which is irreplaceable
in the production of medicines and pesticides. However, traditional
separation methods suffer from great energy consumption, cumbersome
operation or use of organic desorbents. Herein, an energy-efficient
and environmentally friendly method is developed through an absorptive
separation strategy based on nonporous adaptive crystals of perethylated
pillar[5]­arene (EtP5) and pillar[6]­arene (EtP6). EtP5 and EtP6 crystals separate p-chlorotoluene from a p-chlorotoluene/o-chlorotoluene equimolar mixture with purities of 99.1%
and 96.1%, respectively and show no decrease in selectivity upon cycling.
The selectivity is attributed to both the stability of the final crystal
structure upon guest capture and suitable host cavity size/shape.
Besides, we discovered the gate-opening behavior changes of EtP5 crystals at different temperatures after absorption of p-chlorotoluene/o-chlorotoluene mixtures
with various p-chlorotoluene fractions, which is
helpful to understand the thermodynamics of the absorption process.

一氯甲苯异构体的分离是获取高纯度对氯甲苯（p-chlorotoluene）的核心工艺，而高纯度对氯甲苯在医药与农药生产中具有不可替代的地位。然而传统分离方法普遍存在能耗高昂、操作繁琐，或需使用有机脱附剂等弊端。本研究基于全乙基化柱[5]芳烃（EtP5）与全乙基化柱[6]芳烃（EtP6）的非多孔自适应晶体，通过吸附分离策略开发出一种节能高效且环境友好的分离工艺。EtP5与EtP6晶体可从对氯甲苯与邻氯甲苯（o-chlorotoluene）的等摩尔混合体系中分离得到对氯甲苯，分离纯度分别可达99.1%与96.1%，且循环使用过程中分离选择性无明显衰减。该分离选择性可归因于两方面：一是客体分子被捕获后晶体结构的稳定性，二是主体空腔尺寸与形状的适配性。此外，我们还发现，在吸附不同对氯甲苯占比的对氯甲苯/邻氯甲苯混合体系后，EtP5晶体的开门吸附行为会随温度发生变化，这一发现有助于深化对吸附过程热力学机制的理解。