A selective oxidative depolymerization of larch lignin to ethyl vanillate by multifunctional catalysts combining alkaline ionic liquid and polyoxometalates with hydrogen peroxide.

Ethyl vanillate (EV) is an important component of flavors and fragrances and has been widely used in the food, pharmaceutical, and cosmetic industries. The highly selective preparation of EV from lignin, the most abundant monophenolic compound in nature, is a great challenge in the field of lignin depolymerization. In this study, the multi-active catalysts from alkaline ionic liquid and polyoxometalates were constructed, which were characterized by acidity, alkaline and oxidizing ability. They can efficiently cleave the CC and CO bonds of larch lignin in an ethanol/water system at 160 °C for 10 h with HO as an oxidizing agent. Vanillin and EV were main products with the phenolic yield of 10.14 wt% and the selectivity of EV was up to 83.63 %. The depolymerization of phenolic and non-phenolic lignin model compounds demonstrated that the cleavage of β-O-4 and C-C bonds contributed to the selective preparation of EV in the catalytic system. The catalyst can be recycled up to 4 times with excellent stability and recoverability. This study provides a new approach for the production of EV, which is promising in the high-valued utilization of larch waste.