Hydrolysis of Lignin α-O-4 Model Compounds Using Strong Acid Catalyst in Water

Abstract

Efficient and sustainable cleavage of α-O-4 ether linkages is a critical initial step in lignin valorization. In this study, we present two highly effective catalytic protocols for the cleavage of C–O bonds in lignin α-O-4 model compounds under mild conditions (100 °C) that do not require organic solvents. Benzyl phenyl ether and its derivatives undergo quantitative conversion at 100 °C in the absence of an organic solvent under two contrasting conditions: aqueous trifluoromethanesulfonic acid (TfOH) yields the hydrolysis products phenol and benzyl alcohol, whereas solid superacid Nafion NR50 yields benzyl-migrated recombination products predominantly under solvent-free conditions. Nafion NR50 was recovered and reused for five consecutive cycles with conversion maintained within experimental error of activity. Non-fluorinated resins undergo the same transformation more slowly, which suggests that a perfluorinated acid is unnecessary. The medium-control principle established here defines the conditions under which condensation can be suppressed during acid-mediated α-O-4 cleavage.