AbstractExtraction of aromatic substances obtained during oxidation of lignin with ionic liquids (ILs)-based molecular oxygen was investigated. It was found that virtually no aromatic substances could be directly extracted with organic solvent until water had been added to the system. The amount of extracted substances increased sharply with an increase in the molar ratio of water to ILs. The distribution constants of aromatic monomers between ILs/water and extracting solvent was obtained by Nernst partition function analysis. The constants fitted well to a second order exponential function model (ExpDec2), which indicated that the activity coefficients of reaction products between ILs and extracting solvent could be tuned by water addition. Among the seven organic solvents tested, ethyl acetate was the most effective, on account of its suitable polarity, while temperature more prominently affected extraction efficiency than time.