Greener agarose esterification using the ionic liquid 1-butyl-3-methylimidazolium bromide as a sustainable and reusable reaction medium

In this study, agarose-succinate (Ag-SA), agarose-phthalate (Ag-PA), and agarose-maleate (Ag-MA) half-esters were synthesized using an ionic liquid solvent ([Bmim]Br) with yields of 49.01%, 43.91%, and 50.75%, respectively, and degrees of substitution (DS) of 0.75, 0.69, and 0.37. Esterification was confirmed via FT-IR spectroscopy through characteristic ester bond absorption bands, while ¹H and ¹³C NMR analyses substantiated structural modifications, including shifts in anomeric and hydroxyl group resonances. Despite moderate yields compared to aqueous medium methods, the ionic liquid facilitated esterification while maintaining the structural integrity of agarose. Regenerated [Bmim]Br demonstrated purity, enabling its reuse. The study highlights the influence of ionic liquid viscosity on reaction efficiency and emphasizes the potential for further optimization of reaction conditions for biopolymer modification. Graphical Abstract