Application of biodegradable cholinium ionic liquids for the extraction of 5-hydroxymethylfurfural (HMF) from honey

5-Hydroxymethylfurfural (HMF), a Maillard reaction product, can be formed when honey is subjected to heat treatment or a long storage time, becoming volatile and toxic depending on its concentration. The fact that, until today, there is no literature data on the extraction of 5-hydroxymethylfurfural (HMF) from honey using ionic liquids directed the investigation of the influence of biodegradable cholinium ionic liquids on the formation of aqueous biphasic systems and the application of these systems for the extraction of HMF from honey. The influence of anions of synthesised ionic liquids on the construction of biphasic systems in which an inorganic salt was used as a salting agent was investigated. Then, the extraction of HMF in these systems was examined, and the mechanisms of HMF extraction using ionic liquids were explained using computer simulations. Examining the effect of cholinium ionic liquids (choline chloride ([Ch][Cl]), cholinium nicotinate ([Ch][Nic]), cholinium propionate ([Ch][Prop]), and cholinium butyrate ([Ch][But])) on the formation of aqueous biphasic systems by comparing the phase diagrams, it was concluded that the ability of ionic liquids to form an aqueous biphasic system with tripotassium phosphate (K₃PO₄) decreases in the following order: [Ch][But] ≈ [Ch][Prop] > [Ch][Nic] > [Ch][Cl]. By applying all tested aqueous biphasic systems for the extraction of HMF from honey, an extraction efficiency of more than 89% was achieved. Complete extraction was achieved using the extraction system with [Ch][But], while the weakest ability to extract HMF was exhibited by the system with [Ch][Cl]. The mechanisms of HMF extraction using ionic liquids are explained on the basis of the optimised structures of the ionic liquid systems with HMF, together with the visualisation of non-covalent interactions, and on the basis of the calculated binding energies ΔG_bin, which can be used as a good predictor of the extraction potential of newly synthesised ionic liquids.