Chloroaluminate Liquid Clathrates: Is It the Cations or the Anions That Drive the Solubility of Aromatics?

Abstract

Three chloroaluminate ionic liquids (ILs), triethyl­ammonium tetrachloroaluminate ([HN222]­[AlCl4]), triethyl­ammonium heptachlorodialuminate ([HN222]­[Al2Cl7]), and tetraethyl­ammonium heptachlorodialuminate ([N2222]­[Al2Cl7]), were employed to investigate liquid clathrate (LC) formation and the relative role of the cation or anion in aromatic solubility. The trend in molar solubilities in all three ILs was found to be benzene > toluene > o-xylene > p-xylene ∼ m-xylene > mesitylene; however, the solubilities in the [AlCl4]− IL were 40–70% lower than those found for the two [Al2Cl7]− ILs, which were nearly equivalent. Attempts to crystallize analogues of the LC phases from aromatic solutions of [N2222]­[Al2Cl7] led to crystalline [N2222]­[Al2Cl7]·C6H6 from benzene and [N2222]­[AlCl4] from all other aromatic solvents. NMR analyses of [HN222]­[AlCl4] and [HN222]­[Al2Cl7] LCs supported the crystallographic analyses, where 27Al NMR confirmed the dynamic speciation of the [Al2Cl7]− anions but not the [AlCl4]− anions, and 1H NMR supported the crystallographic observation that each benzene interacts with two cations; however, the solution data suggested a 2:1 benzene/IL ratio.

Understanding liquid–liquid equilibria in binary mixtures of hydrocarbons with a thermally robust perarylphosphonium-based ionic liquid

“…These numbers are similar to those recently determined for aromatics in alkylammonium chloroaluminates. 34 As with toluene, the ions of all hydrocarbon-IL mixtures are in close proximity to an abundant hydrocarbon phase, albeit to varying degrees: ethylbenzene and m-xylene (6-7); toluene, o-xylene, napthalene, bromobenzene, and cyanobenzene (12)(13)(14); p-xylene and hexa-uorobenzene (24-26). These differences may arise from differences in channel width or local curvature at the subphase interface, though this was not apparent from visual inspection of the trajectories.…”

“…[29][30][31] Interestingly, it is found that formation depends on the strength of the cation-anion interaction and that aromatic solubility is inversely proportional to this strength. [32][33][34] Additionally, interactions with the nonpolar domain of an IL are also likely to play a role 23 since aromatic hydrocarbons are shown to be soluble in non-aromatic ILs. 35,36 Likely each of these factors plays a role to some degree, however until a clearer picture emerges of the molecular interactions leading to this phenomena, it remains difficult to tune the structure for optimal control over separation.…”

Solubility of Xylene Isomers in Seven Deep Eutectic Solvents

“…The solubility of p -xylene was higher than that of m -xylene in TBAB/EG (1:4) and TBAB/TEG (1:4), but the relationship between the magnitude of the solubility of the two isomers was reversed in TBAB/DEG (1:4). It has been reported , that this o -xylene > p -xylene ∼ m -xylene solubility law is also present in ionic liquids and is likely caused by the effect of the differences in the dipole moments. In addition, the solubility of the HBDs increased with increasing chain length.…”

“…The solubility of o -xylene increased faster than the other two isomers and was higher than that of the other two isomers. This phenomenon was attributed to the differences in the induced dipole moment, which is related to the molecular structure. − Thus, the structure of the HBAs affected the solubility of the three isomers.…”

Recyclable Magnetic Fe3O4 Nanoparticle-Supported Chloroaluminate Ionic Liquids for Heterogeneous Lewis Acid Catalysis

“…The ILs [HN 222 ]­[Al 2 Cl 7 ] and [HN 222 ]­[AlCl 4 ] were prepared by following our previously reported procedures. , Both were prepared by reacting solid [HN 222 ]Cl (20 mmol, 2.76 g) with solid anhydrous AlCl 3 (20 mmol (2.67 g) or 40 mmol (5.34 g)) at a 1:1 or 1:2 molar ratio under an Ar atmosphere, to produce the colorless solid [HN 222 ]­[AlCl 4 ] and liquid [HN 222 ]­[Al 2 Cl 7 ].…”