Porous materials, which can capture a specific compound from a hard-to-separate molecular mixture, are strongly desired for practical separation and purification processes. Aiming to develop such materials, we have investigated the performance of our original host compounds, [3,3′-thiobis(5-tert-butyl-2-hydroxybenzene)-1,1′-diyl]diacetic acid (2) and its monopropyl ester (3), in discriminating among regio- or stereoisomers of three groups of amines, 2-, 3-, and 4-methylpyridine, 2-, 6-, and 8-methylquinoline, and cis- and trans-4-cyclohexanamine. Diacid 2 selectively included 4-methylpyridine in hexane and 3-methylpyridine in toluene in competitive inclusion among the three regioisomers. Mechanistic studies revealed that the inclusions of 3- and 4-methylpyridine are favored under kinetic and thermodynamic control, respectively. Solvent-dependent switching in guest selectivity was also observed in competitive inclusion among the methylquinoline isomers with diacid 2, whereas trans-4-methylcyclohexanamine was selectively included over the cis-isomer by monoester 3, as well as diacid 2, regardless of the solvent employed. X-ray crystallographic analysis of the resulting inclusion crystals suggests that the wide guest scope of the host compounds originates from their flexible ability to form complexes with amines.
ASJC Scopus subject areas
- Organic Chemistry