Discrimination between o-xylene, m-xylene, p-xylene and ethylbenzene by host compound (R,R)-(–)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol

The title host compound (R,R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol 3, when recrystallized from each of the isomeric xylenes and ethylbenzene, formed a 2:1 host:guest complex in each instance. Competition experiments where 3 was recrystallized from various equimolar binary, ternary and quaternary mixtures of these guests indicated that 3 displayed a consistent preference for para-xylene whenever it was present: when 3 was recrystallized from equimolar binary and ternary mixtures of the xylenes, the selectivity order was para-xylene ≫ ortho-xylene > meta-xylene while recrystallization from equimolar binary and quaternary mixtures of the xylenes and ethylbenzene showed a selectivity order of para-xylene > ethylbenzene > ortho-xylene > meta-xylene. Thermal experiments showed that the higher the relative thermal stability of the complex, the higher was the host's preference for it. However, no dominant differences in the strength or nature of intermolecular host-guest interactions could be singled out from crystal data to explain these observations.

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