Evaluation of the Behavior of Two Tricyclic-Fused Host Systems in the Presence of Single and Mixed Isomers of the C₈H₁₀ Aromatic Crude Oil Fraction

Abstract

In this investigation, potential host compounds N, N′-bis(9-phenyl-9-xanthenyl)propane-1,3-diamine (H1) and N, N′-bis(9-phenyl-9-xanthenyl)butane-1,4-diamine (H2) were crystallized from pure single solvents and mixtures of guests comprising xylenes (oXy, mXy, and pXy) and ethylbenzene (EB). Although H1 successfully enclathrated oXy in the single solvent experiment, this host compound was not able to extract oXy when presented with various mixtures of these guest compounds, and only the guest-free host compound was ultimately recovered from these crystallization experiments. H2, on the other hand, successfully included both oXy and pXy. Thermal experiments on H2•pXy and H2•1.5(oXy) showed that the former complex was more stable than the latter. Single-crystal X-ray diffraction (SCXRD) experiments were employed to analyze the conformations of both host molecules when guest-free and in the presence of the guest species. Experiments involving equimolar binary guest mixtures and H2 revealed that this host compound was selective for oXy whenever it was present. Furthermore, from experiments employing H2 and pXy/mXy (40:60, 50:50, and 60:40 mol %) binary mixtures, remarkable K values (the selectivity coefficient) were calculated in favor of pXy, suggesting that host−guest chemistry strategies may be used to effectively separate these difficult-to-separate mixtures when H2 is the host compound.