Separation of mandelic acid enantiomers using solid-liquid biphasic systems with chiral ionic liquids


This work aims to take full advantage of ionic liquids' (ILs) designer solvent nature in order to expand the applicability of solid-liquid biphasic systems (SLBS) as alternative chiral resolution techniques. To this purpose, twelve chiral ILs, bearing chirality on the cation or the anion, were used as chiral selectors in SLBS to selectively precipitate mandelic acid enantiomers. The precipitation studies were performed using aqueous solutions of the chiral ILs or their chiral precursors, where the impact of the chemical structure and chirality was investigated. The most efficient chiral ILs were employed to evaluate the influence of different operational conditions on the formed precipitate, namely resolution time, resolution speed, temperature, initial concentration of chiral IL, initial concentration of racemic mandelic acid and water content. When compared to their precursors, chiral ILs showed an enhanced ability to induce enantioselective precipitation. The composition of the precipitate formed, and the molecular-level mechanisms leading to enantioselective precipitation, were also uncovered. Due to cooperative interactions between the chiral IL and the target mandelic acid enantiomer, the [N-4444][D-Phe]based SLBS proposed allowed to obtain maximum enantiomeric excess of 51% in a single-step, without any further additives.



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Kholany, M; Silva, FAE; Sintra, TE; Brandao, P; Ventura, SPM; Coutinho, JAP

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This work was developed within the scope of the project CICECOAveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. This work was also financially supported by the project POCI-01-0145-FEDER-030750 (PTDC/EQU-EPQ/30750/2017) -funded by FEDER, through COMPETE2020 -Programa Operacional Competitividade e Internacionalizacao (POCI), and by national funds (OE), through FCT/MCTES. The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project N degrees 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). M. Kholany acknowledges FCT for the doctoral grant SFRH/BD/138413/2018.

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