Selective Production of Diethyl Maleate via Oxidative Cleavage of Lignin Aromatic Unit

Summary

Green production of bulk chemicals traditionally obtained from fossil resources is of great importance. One potential route toward realizing this goal is through the utilization of renewable lignin; however, current techniques generally lead to low product specificity because of the structural diversity of this recalcitrant biopolymer. Herein, we devised a new catalytic system to promote selectively oxidative lignin in air, and diethyl maleate was formed at impressively high yield of 404.8 mg g⁻¹ and selectivity of 72.7% over the polyoxometalate ionic liquid of [BSmim]CuPW₁₂O₄₀. This high catalytic activity is ascribed to a five-coordinated Cu⁺ species, which, through the formation of end-on dioxygen species in vacant orbitals, facilitates the selective oxidation of basic lignin aromatic units (phenylpropane C₉ units). Therefore, these results represent significant progress toward the realization of an industrially applicable and highly selective lignin oxidation process for the generation of value-added and bulk chemicals.