Recovery of host crystals from inclusion crystals of p-tert-butylcalix[4]arene and p-tert-butylthiacalix[4]arene by the treatment with a solvent and/or supercritical CO2

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p-tert-Butylcalix[4]arene (1) crystals can selectively include one regioisomer from a mixture of the three regioisomers for eight kinds of disubstituted benzenes. In this study, the mechanisms for the guest selectivity in the inclusion of nitrotoluene, xylene, and cresol isomers, which were chosen as representative guests showing different guest selectivity, were investigated in detail. In the competitive inclusion of three regioisomers of nitrotoluene, xylene, and cresol, crystals of compound 1 selectively include pnitrotoluene, p-xylene, and o-cresol, respectively. Time course of the change in isomer selectivity in the competitive inclusion experiment and comparison of thermogravimetric analysis profiles of the inclusion crystals with each of the isomers revealed that the selectivity for p-nitrotoluene and o-cresol was achieved under kinetic control, whereas the selectivity for p-xylene was achieved under thermodynamic control. X-ray crystallography of the inclusion crystals revealed that p-nitrotoluene and o-cresol form type A (host/ guest = 1:1) inclusion crystals, in which a guest molecule is included in the cavity of a host molecule. On the other hand, o-and mnitrotoluene and m-and p-cresol form thermodynamically stable type B (host/guest = 2:1) inclusion crystals, in which a guest molecule is included in a capsule constructed by gathering of two host molecules in a head to head manner. The selectivity for pnitrotoluene and o-cresol could be explained by the effective host−guest interaction during the formation of type A inclusion crystals, which tends to be kinetically favored over the formation of type B inclusion crystals. X-ray structure analysis and Hirshfeld surface analysis of the inclusion crystals revealed that the inclusion of xylene isomers in the crystals of compound 1 resulted in the formation of type B inclusion crystals for all the three isomers. The CH−π interaction between the two methyl groups of the p-isomer and the benzene rings of the two host molecules encapsulating the isomer is the most effective. Therefore, the inclusion crystal with p-xylene is the most stable among the three isomers, resulting in p-isomer selectivity. In this way, the crystals of compound 1 precisely distinguish different disubstituted benzene isomers under kinetic or thermodynamic control by the virtue of various host−guest interactions with the guest substituents in the cavities of type A and type B inclusion crystals.

Section: Introductionmentioning

confidence: 99%

Mechanistic Consideration for the Selective Inclusion of Disubstituted Benzene Isomers with p-tert-Butylcalix[4]arene Crystals

Matsumoto

Sasaki

Tonosaki

et al. 2021

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“…Calixarene is one of the representative host molecules that afford NMCs without channel structures. Their inclusion behavior toward organic molecules and inorganic gases has been actively investigated. − We have engaged in the development of selective inclusion methods for various organic molecules with crystals of calixarene without channel structures. − For example, the selective inclusion of alcohols, , carboxylic acids, , and amines with crystals of p - tert -butylthiacalix[4]arene has been already achieved. The guest selectivity can be switched in several cases. ,, Very recently, we also reported the application using salt crystals to the selective collection of lanthanide ions from water .…”

Section: Introductionmentioning

confidence: 99%

Selective Inclusion of Cyclohexanediol Stereoisomer by Crystals of Open-Chain Diol-Type Host Based on a Partial Structure of p-tert-Butylthiacalixarene

Morohashi,

Suzuki,

Ogihara

et al. 2024

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For the efficient separation of hard-to-separate organic molecule isomers, the creation of solid materials that can distinguish between isomers and selectively collect them is important. For example, in the separation of organic molecule isomers that have multiple functional groups such as hydroxy groups, the design of host molecules that allow the precise recognition of the positions and orientations of the functional groups is required. In this study, based on sulfur-bridged phenol dimer that is a partial structure of p-tert-butylthiacalixarene, an open-chain diol-type host 2 was designed and synthesized. In compound 2, two phenolic hydroxy groups were bridged with a methylene group to fix the conformation, and two alcoholic hydroxy groups were introduced for guest recognition sites. In a competitive inclusion experiment from an aqueous solution of a cis/trans mixture of 1,3-cyclohexanediol, crystals of host 2 selectively included cis-isomer. The isomer selectivity was low for the inclusion of 1,2-diol, and 1,4-diol was not included. X-ray crystallographic analysis of the inclusion complex of host 2, which predominantly included the cis-isomer of 1,3-diol, revealed that two hydroxy groups of the host form cooperative hydrogen bonds with two hydroxy groups of the guest. The results show that densely packed stable crystals can be formed by fixing the conformation of the host to construct an inclusion space and by the precise recognition of the guest functional groups complementary to the host molecule. This study provides an approach for the design of host molecules that can selectively include difficult-to-separate target molecules.

“…Calixarene, such as p - tert -butylcalix[4]arene ( 1 ) or p - tert -butylthiacalix[4]arene ( 2 ) (Chart ), is a typical host molecule that gives NMC having no empty channel structures, − whereas most NMCs form clathrate-type inclusion crystals in which the guest compound is included in the lattice constructed by the host compound. − The inclusion behavior of organic molecules and inorganic gases with crystals of calixarenes has been widely studied by the research groups of Atwood, − Ripmeester, − Gorbatchuk, − and Tsue. − Recently, the recognition of organic molecules with crystals of thiacalix[4]arene derivatives having channel structures has also been studied by Yamada and Hamada’s group. , Achieving the selective inclusion of alcohol using the crystals of compound 2 , we have developed selective inclusion methods for various organic molecules. − Calixarene crystals can construct complex-type inclusion crystals consisting of discrete host–guest complexes, accompanied by structural changes. Therefore, the difference between guest structures is easily reflected in the difference between the thermal stabilities of the crystal structures (thermodynamic control) and their activation energies during phase transition, which can also be used to introduce selectivity (kinetic control).…”

Section: Introductionmentioning

confidence: 99%

Switching of Guest Selectivity for the Inclusion of Regioisomers of Monosubstituted Phenols with Crystals of p-tert-Butylcalix[4]arene

Morohashi

Sakamoto

Matsumoto

et al. 2023

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To develop an inclusion method for hard-to-separate organic molecules with wide guest scopes, we examined the control of guest selectivity via external factors such as solvents, temperature, and additives for the competitive inclusion of monosubstituted phenol isomers with crystals of p-tert-butylcalix[4]arene 1. Guest selectivity was thus switched between two isomers in the inclusion of cresol, fluorophenol, and bromophenol and between three isomers in the inclusion of chlorophenol. The mechanism of guest selectivity in chlorophenol inclusion was mainly determined using X-ray crystal structural analysis and a comparison of the thermal stabilities and the formation rates of inclusion crystals with each isomer. Under kinetic control, the inclusion from decane at a low temperature selectively yielded type-A (host/guest = 1:1) inclusion crystals of p-isomer (1·p-chlorophenol) in which the host and guest molecules exhibited CH−π and OH–π interactions. In aqueous solutions at high temperatures, where water molecules inhibited the inclusion of m-isomer, thermally stable type-B (host/guest = 2:1) crystals of o-isomer (1 2·o-chlorophenol), in which a guest molecule was included in a capsule constructed by two host molecules, selectively formed. Furthermore, the inclusion from decane in the presence of methanol produced a co-inclusion crystal of type-C (host/guest/additive = 2:1:1) in which a 1:1 complex of m-isomer and methanol, connected via an intermolecular hydrogen bond, was selectively included by the distorted capsule of two host molecules to form 1 2·m-chlorophenol·CH3OH.