trans-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic Acid: Remarkable Host Selectivities in the Presence of Mixtures of Anisole and Bromoanisole Isomers

Abstract

In this work,, a host compound that formed complexes with anisole (ANI), 2-bromoanisole (2-BA), and 4-bromoanisole (4-BA), was revealed to possess a remarkable affinity (93.1−98.6%) for 4-BA when recrystallized from any mixtures containing this guest species, be these binary (ANI/4-BA, 2-BA/4-BA, or 3-BA/4-BA), ternary (ANI/2-BA/4-BA, ANI/3-BA/4-BA, or 2-BA/3-BA/4-BA), or quaternary (ANI/2-BA/3-BA/4-BA) in nature. Furthermore, this striking host selectivity persisted even in binary solutions containing low concentrations of 4-BA (18−25%); near-complete selectivities in favor of 4-BA were observed here too. Single crystal X-ray diffraction analyses showed that the favored guest species, 4-BA, was the only one to experience short intermolecular contacts, through its phenyl ring, with the host molecule's carbonyl oxygen atom and the host hydrogen atom on the carbon bearing the second carboxylic acid group. Furthermore, ANI and 2-BA were accommodated in wide open channels, while the guest accommodation type for 4-BA was significantly more constricted. Thermal analyses confirmed that 2(DED)•3(ANI) and DED•2-BA, having the disfavored guests in open channels, were unstable at room temperature, while the preferred guest species, 4-BA, in its decidedly constricted channels, was only released at significantly higher temperatures (116.8 °C). Therefore, by employing host−guest chemistry strategies, DED has the ability to purify and separate any of these 4-BA-containing mixtures, a distinct advantage over fractional distillations which are cumbersome owing to physical property similarities of 2-, 3-, and 4-BA.

Host Compound DED: Guest Accommodation Type, Noncovalent Host···Guest Interactions, Crystal Densities, and Thermal Stabilities Ensure High Host Selectivities for 4-Methylanisole in Anisole and Methylanisole Mixtures

“…The characteristics of the 2­( DED )·3­(ANI) complex have already been reported, and ANI was shown to occupy wide open and multidirectional channels and, as a result, the thermal stability of this complex was described as low; thermal experiments suggested that some of the guest species present were released from the crystals of the complex even at ambient conditions. In that work, which employed ANI and the bromoanisole isomers in mixtures, ANI was also shown to be a disfavored guest, as is the case in the present investigation.…”

“…2-MA and 3-MA commenced escape from the crystals at 90.4 and 85.3 °C, respectively, while the complex containing ANI was unstable under ambient conditions. 31 Expected and measured mass losses corresponded (17.2 compared with 17.0, 17.2, and 17.4% for 2(DED)•2-MA, 2(DED)•3-MA, and 2(DED)•4-MA, respectively) with the exception of the unstable ANIcontaining complex. Finally, the guest release event was followed in each case by the host melt (240.7−243.8 °C) and, finally, its decomposition.…”

“…These data pertaining to 2(DED)•3(ANI) were deposited on a prior occasion (CCDC 2211030). 31 Two gas chromatography (GC) methods were employed to quantify the guest proportions in any mixed complexes formed in this work. The first of these used a Young Lin YL6500 gas chromatograph equipped with an Agilent J&W Cyclosil-B column coupled to a flame ionization detector.…”

“…The crystallographic data for 2­( DED )·2-MA, 2­( DED )·3-MA, and 2­( DED )·4-MA were deposited at the Cambridge Crystallographic Data Centre (CCDC), and their CCDC numbers are 2214288, 2214289, and 2214290, respectively. These data pertaining to 2­( DED )·3­(ANI) were deposited on a prior occasion (CCDC 2211030) …”

“…(In 2(DED)•3(ANI) were observed four C−H•••π interactions between DED and ANI molecules, and the H•••π distances measured between 2.73 and 2.90 Å (122−151°). 31 )…”