Separation of Lutidine Isomers by Selective Enclathration

Here, we report on the results obtained when trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (DED) crystals were grown from mixtures containing equimolar isomeric o-, m-, and p-dichlorobenzenes (o-DCB, m-DCB, and p-DCB). DED displayed a remarkable affinity for p-DCB in both binary and ternary recrystallization experiments involving this guest species, and near-quantitative amounts of p-DCB were measured in the resultant crystals (96.4−100.0%). The host selectivity was in the order p-DCB >>> m-DCB > o-DCB. This enhanced selectivity for p-DCB was also evident in binary mixtures in which molar quantities of the guests were varied: when employing 39/61% p-/o-DCB and p-/ m-DCB, the recovered crystals contained as much as 83 and 98% p-DCB, respectively. At higher concentrations of p-DCB, DED then selected only this guest compound. Single-crystal X-ray diffraction experiments revealed that while host•••guest interactions did not appear to be an important factor that guided the host selectivity behavior, the type of guest accommodation did indeed, and the preferred guest, p-DCB, was tightly held in highly constricted channels, while some of the other two isomers were retained in wide, open channels. Thermal analysis experiments confirmed this observation, and complexes in which some of the guests occupied wide, open channels possessed lower thermal stabilities compared with the p-DCB-containing complex, where the channels were significantly more constricted.

Section: Introductionmentioning

confidence: 99%

trans-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic Acid: Complete Host Selectivity for Guest Compound para-Dichlorobenzene during Crystal Growth from Mixed Isomeric Dichlorobenzenes

Barton

Caira

Senekal

et al. 2022

“…More relevant to the present work is the employment of host compounds for the separation of isomers, both constitutional and stereoisomers. For example, Seebach et al expounded upon the use of optically pure α,α,α′,α′-tetraaryl-2,2-disubstituted 1,3-dioxolane-4,5-dimethanols (TADDOLs) for the resolution of racemates, while Nassimbeni and Barbour and co-workers reported on how host–guest chemistry may be employed in order to facilitate the separation of isomeric lutidines and xylenes, respectively. , …”

Section: Introductionmentioning

confidence: 99%

“…For example, Seebach et al expounded upon the use of optically pure α,α,α′,α′-tetraaryl-2,2-disubstituted 1,3-dioxolane-4,5-dimethanols (TADDOLs) for the resolution of racemates, 15 while Nassimbeni and Barbour and co-workers reported on how host−guest chemistry may be employed in order to facilitate the separation of isomeric lutidines and xylenes, respectively. 16,17 In our own laboratories, we designed and synthesized the compound (−)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) in order to investigate its host potential for the separation or purification of mixtures of ANI and the three MANIs in the search for the optimal host species for this process. Some host selectivity was observed: for example, in equimolar ANI/oMANI, oMANI/pMANI, and ANI/mMANI binary mixtures, the selectivity was for ANI, pMANI, and ANI, respectively (92.6, 88.8, and 86.7%).…”

Section: Introductionmentioning

confidence: 99%

Selectivity Considerations of the Roof-Shaped Host Compound trans-α,α,α′,α′-Tetrakis(4-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol in Mixed Anisoles

Barton

Caira

Senekal

et al. 2022

The roof-shaped host compound trans-α,α,α′,α′tetrakis(4-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol H1 was assessed for its selectivity behavior in various anisole (ANI) and ortho-, meta-, and para-methylanisole (oMANI, mMANI, and pMANI) mixtures. Guest/guest competition experiments in equimolar binary mixed guest solvents revealed remarkable host selectivities for ANI or mMANI when oMANI or pMANI was also present (90.7−95.3%). Furthermore, the oMANI/pMANI experiment proved H1 to be nearly completely selective for oMANI (91.8%). In ternary experiments, unexpectedly high selectivities toward ANI (82.6%) and mMANI (89.5%) were noted when the solutions were ANI/oMANI/pMANI and oMANI/mMANI/pMANI. Data obtained from binary competition experiments in which the molar quantity of each guest species was sequentially varied correlated exactly with these equimolar experiments, and high selectivity coefficients were calculated for ANI and mMANI when either oMANI or pMANI was also present. Unfortunately, SCXRD analyses on H1•ANI, 2H1•oMANI, and 2H1•pMANI revealed extreme guest disorder, and these could not be modeled. However, in H1•mMANI, the guest molecules were retained in the crystals by means of a close (host)C−H•••π(guest) contact (2.97 Å, 143°). Finally, thermal analyses proved less useful in explaining the observed host selectivity. This work demonstrates that H1 is an extremely selective host compound in very many of the anisole mixtures used in this investigation and, therefore, is a highly suitable candidate to effectively separate and purify such mixtures.

“…Other isomer mixtures where separation has been carried out in this manner include the isomers of lutidine, phenylenediamine, trimethoxybenzene, and methyl and dimethylpiperidines . The process of inclusion consists of exposing a host to a guest molecule in order to form a host–guest complex or clathrate.…”

Section: Introductionmentioning

confidence: 99%

“…Mixtures of isomers often present a separation problem, and the example that is often cited is the case of the isomers of xylene, where normal boiling points vary from 138.4 to 144.4 °C, and their separation by host−guest inclusion has attracted significant attention. 3−7 Other isomer mixtures where separation has been carried out in this manner include the isomers of lutidine, 8 phenylenediamine, 9 trimethoxybenzene, 10 and methyl and dimethylpiperidines. 11 The process of inclusion consists of exposing a host to a guest molecule in order to form a host− guest complex or clathrate.…”

Section: Introductionmentioning

confidence: 99%

Enclathration of Picoline Isomers by (rac)-TADDOLs: Structures, Selectivity, and Thermal Analysis

Tiffin

Sykes

Weber

et al. 2019

Self Cite

In this investigation, we studied the preferences of three α,α,α′,α′-tetraphenyl-l,3-dioxolane-4,5-dimethanol (TAD-DOL)-derived host compounds toward the isomers of methylpyridines (picolines). Ten novel inclusion compounds were synthesized, and their structural and thermal properties were further characterized. Binary competition experiments were performed, and all three hosts discriminate between the picoline isomer guests. Interestingly, all three hosts display different preferences toward the isomers, and these results were rationalized by their resulting crystal structures and packing analysis and correlated to their differential scanning calorimetry (DSC) results. DSC results showed a correlation between the thermal stability of an inclusion compound and the preference of the host toward a given isomer.