Abstract
A method for the separation of stereoisomer mixture of the octol C-tetra(p-hydroxyphenyl)calix[4]resorcinarene that was obtained by an acid cyclocondensation reaction between resorcinol and benzaldehyde is reported in this paper. A crude product from octol formation reaction was analyzed by reverse-phase high-performance liquid chromatography (RP-HPLC), and two well-resolved signals corresponding to the crown and chair isomers were found. A reverse phase in solid-phase extraction (RP-SPE) protocol allowed the separation of the two stereoisomers with high purity of each isomer. Finally, the crude and purified stereoisomers were characterized by using FT-IR, 1H-NMR, and 13C-NMR techniques, confirming the chemical identity of the two isomers and the efficiency in the separation process.
Highlights
Resorcinarenes are macromolecules with four resorcinol rings linked by methylene bridges [1, 2], and they have wide applications in chemical separations [3, 4], in NMR techniques as solvating agents [5], and as chemosensors [6,7,8,9], among others
Resorcinarenes with substituted methylene bridge are found in crown structure in the crystal state [17,18,19], and in solution, the isomer may adopt crown and chair structures [20, 21]; the chair structure can interconvert in the crown structure at high-temperature conditions in the presence of highly polluting metal catalysts [22, 23]
Continuing with our studies related to structure and applications of resorcinarenes [33,34,35,36], in the present investigation, we show an efficient method for the analysis of this kind of stereoisomers by RPHPLC and it is shown that the mixture can be separated by means of the RP-SPE technique with good yields
Summary
Resorcinarenes are macromolecules with four resorcinol rings linked by methylene bridges [1, 2], and they have wide applications in chemical separations [3, 4], in NMR techniques as solvating agents [5], and as chemosensors [6,7,8,9], among others. Acid-catalyzed condensation reaction by choosing aromatic aldehyde as a starting material usually produces a conformational mixture of two stereoisomers, in different proportions, known as chair and crown (see Figure 1) [13,14,15,16]. Of these isomers, the crown stereoisomer is the thermodynamically stable compound; alternatively, the structure of resorcinarenes can be rigidified into a crown by linking the hydroxyl groups of the upper rim, which provides a higher degree of preorganization. Continuing with our studies related to structure and applications of resorcinarenes [33,34,35,36], in the present investigation, we show an efficient method for the analysis of this kind of stereoisomers by RPHPLC and it is shown that the mixture can be separated by means of the RP-SPE technique with good yields
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