RESUMO
Conventional distillation methods cannot separate compounds with similar boiling points, molecular sizes, and volumes, such as cyclohexane and benzene or methylcyclohexane and toluene, effectively. The corresponding cyclic aliphatic and aromatic hydrocarbons cannot be separated effectively using the same type of sorption material. We report that crystalline thiacalixarene assemblies featuring preorganized channel-like adsorption sites are capable of both separations.
RESUMO
Invited for the cover of this issue is the group of Manabu Yamada at Akita University and colleagues from Yamagata University and Vellore Institute of Technology. The image depicts two activated "channel-like" crystals, effectively adsorb branched and cyclic alkanes from linear, branched, and cyclic alkane vapors. Read the full text of the article at 10.1002/chem.202000043.
RESUMO
Alkanes composed of C-C and C-H show a low electric polarization, and therefore, there is only very weak interaction between alkanes and adsorbents. Thus, it is difficult to separate a specific alkane from a mixture of alkanes by adsorption. Here, two activated "channel-like" crystals generated from brominated thiacalix[4]arene propyl ethers, which adopt 1,3-alternate and partial cone conformations, recognize specific alkane vapors depending on alkane-shape and -size, sorting in three-type alkane guests such as linear, branched, and cyclic alkanes. Two activated crystals, which are prepared by removal of solvent upon heating under reduced pressure, incorporate branched and/or cyclic alkane vapors by a unique "gate-opening" mechanism via a crystal transformation in the process. Linear alkane vapors do not trigger gate opening and are not taken up by the activated crystals. The shape and size molecular-recognition properties of the activated crystals promises considerable usefulness for the separation of linear, branched, and cyclic alkanes.
