Highly efficient separation of strongly hydrophilic structurally related compounds by hydrophobic ionic solutions

The selective separation of strongly hydrophilic structurally related compounds in aqueous solutions is a long‐standing challenge due to a trade‐off between separation selectivity and capacity. This work shows a new method to separate strongly hydrophilic structurally related compounds through hydrophobic ionic solution‐based liquid‐liquid extraction, with L‐ascorbic acid 2‐glucoside (AA‐2G) and L‐ascorbic acid as model compounds. Extraordinary distribution coefficient, superb molecular selectivity, large extraction capacity and good recyclability without using strong acids and salts were all achieved, with a small consumption of phosphonium bromide ionic liquid and aprotic molecular diluent. The essence of this method is the successful combination of both strong hydrogen‐bond basicity and good hydrophobicity along with significant preferential solvation phenomena of the constructed ionic solutions. Even if at a high feed concentration of 100 mg/mL, the purity of AA‐2G could be greatly elevated from 50% to 96.2% with an ultrahigh yield of almost 100% after five‐stage countercurrent extraction. © 2017 American Institute of Chemical Engineers AIChE J , 64: 1373–1382, 2018