Mercapto-β-cyclodextrin covalent organic frameworks for enantioselective liquid-liquid extraction

Abstract

β-Cyclodextrin (β-CD) exhibits exceptional chiral recognition ability, and covalent organic frameworks (COFs) have been reported as highly promising chiral carriers. Therefore, incorporating cyclodextrin into COFs may result in chiral covalent organic frameworks (CCOFs) suitable for chiral applications. In this work, a solvothermal method was employed to synthesize a classical porous covalent organic framework (COF-V), while β-CD underwent a two-step modification process, resulting in the synthesis of mercapto-β-cyclodextrin (β-CD-SH). Subsequently, a β-CD-based covalent organic framework (COF-S-CD) was synthesized through a Thiol-Ene “click” reaction. The synthesized COF-S-CD was successfully applied in enantioselective liquid-liquid extraction for five racemic arylcarboxylic acids, including 2-phenylpropionic acid, 2-(4-methylphenyl) propionic acid, 2-(3-chlorophenyl) propionic acid, 2-(4-nitrophenyl) propionic acid and α-cyclohexylmandelic acid. Under optimized conditions, enantioseparation factors for the five racemates reached 1.78, 2.20, 1.84, 1.76 and 1.96, respectively, which indicated a significant enhancement in chiral recognition ability upon the incorporation of cyclodextrin into the COF material. This new application suggested that the synthesis of covalent organic framework materials incorporating β-CD, with the ability to uniformly disperse in the aqueous phase, holds promising potential for highly effective enantioselective liquid-liquid extraction.