Selective extraction of polyhydroxy compounds using hydrophobic ionic liquids

Polyhydroxy compounds such as sugar alcohols /derivatives are high value chemicals with application potential in medicine, materials and other fields. Researches on preparation and selective extraction of polyhydroxy compounds have attracted wide attention in the world. However, the selective extraction of polyhydroxy compounds is still a major challenge. In this paper, hydrophobic ionic liquids (ILs) 1-butyl-3-methylimidazole bis(trifluoromethanesulfon)imide salt ([Bmim][Ntf₂]), 1-ethyl-3-methylimidazole bis(trifluoromethanesulfon)imide salt ([Emim][Ntf₂]) and 1-allyl-3-methylimidazole bis(trifluoromethanesulfon)imide salt ([Amim][Ntf₂])) were used for the dissolution and selective extraction of polyhydroxy compounds. In addition, the interaction between ionic liquids and polyhydroxy compounds was characterized and analyzed by NMR and contact angle analysis. The partition coefficients of polyhydroxy compounds in water and hydrophobic ionic liquids were also investigated. It was shown that among the ILs used, the solubility of polyhydroxy compounds fluctuated strongly (from 0 wt% to 19.50 wt%), and the solubility in [Amim][Ntf₂] was the highest. These hydrophobic ionic liquids showed strong selective extraction ability when fractionating mixtures composed of sugar alcohols and their dehydrated derivatives (1:1, w / w). The results showed that the purities of isosorbide and isomannide separated were more than 99.60 wt% and 99.99 wt% respectively. Polyhydroxy compounds dissolved in hydrophobic ionic liquids could be directly extracted by water without chemical modification. The regeneration rate of ionic liquids reached 93.22%−97.04%. The NMR characterization of the regenerated ionic liquid showed that water could fully extract polyhydroxy compounds dissolved in the ionic liquids and the structure of the regenerated ionic liquid did not change. It was promising to construct a green and efficient method for fractionating such polyhydroxy compounds based on hydrophobic ionic liquids, and it is suggested to further strengthen the research in this field.