Alternative purification protocols of mixed pyridines in the presence of trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-diamine

Abstract

In this communication, we reveal that the host compound trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,4-diamine (1,4-DAX) possesses the ability to purify 2-methylpyridine (2MP)/pyridine (PYR) and 3-methylpyridine (3MP)/PYR binary mixtures by enclathrating PYR almost exclusively, even when such mixtures contained as little as approximately 30% PYR. For example, when these solutions were prepared with equimolar quantities of the two guests, complexes contained as much as 92.4 and 96.4% PYR, respectively. Furthermore, 1,4-DAX was capable of forming a mixed complex with as high as 87.8% PYR from an equimolar ternary mixture containing 2MP, 3MP and PYR through host?guest complexation. This work complements that of trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,2-diamine (1,2-DAX) and trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,2-diamine (1,2-DAT), disclosed in a previous submission, where 4-methylpyridine (4MP) and 2MP, correspondingly, were the preferred guest solvents. Interestingly, trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,4-diamine (1,4-DAT) showed no inclusion tendencies under such conditions. Successfully-formed inclusion complexes were subjected to crystal X-ray diffraction analyses in order to understand the preference of 1,4-DAX for 4MP and PYR. Thermal analyses of these complexes were, however, less informative.