Two-Step, Catalytic C–C Bond Oxidative Cleavage Process Converts Lignin Models and Extracts to Aromatic Acids

Abstract

We herein report a two-step strategy for oxidative cleavage of lignin C–C bond to aromatic acids and phenols with molecular oxygen as oxidant. In the first step, lignin β-O-4 alcohol was oxidized to β-O-4 ketone over a VOSO4/TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl)­oxyl)] catalyst. In the second step, the C–C bond of β-O-4 linkages was selectively cleaved to acids and phenols by oxidation over a Cu/1,10-phenanthroline catalyst. Computational investigations suggested a copper-oxo-bridged dimer was the catalytically active site for hydrogen-abstraction from Cβ–H bond, which was the rate-determining step for the C–C bond cleavage.

Metal Catalyst‐Free Oxidative C−C Bond Cleavage of a Lignin Model Compound by H2O2 in Formic acid

“…There have also been fewer reports on tandem reactions for the more difficult C α −C β bond cleavage via the ketone‐structured LMC (Scheme ). As a good example, Wang and co‐workers developed a two‐step process for C α −C β cleavage of LMC . The β‐O‐4 alcohol LMC was oxidized to β‐O‐4 ketone LMC by using pressurized oxygen and a VOSO 4 /TEMPO catalyst system, and then cleaved by pressurized oxygen in the presence of an organometallic Cu complex.…”

Visible‐Light‐Driven Cleavage of C−O Linkage for Lignin Valorization to Functionalized Aromatics

“…[40] The photocatalytic depolymerization process is illustrated in Figure 6a.T he yellow-brown dioxasolv birch lignin solution in methanolw as decoloreda fter the reaction, which indicated ar educed molecular weight of the substrate. [41] The liquid productsw ere extracted with CH 2 Cl 2 and analyzed by GC-MS and GC. Based on the Aa integralso f2 DH SQC NMR spectra before and after the photocatalyticr eaction, approximately 85 %o fb-O-4 was cleaved (Figure 6b).…”

Mechanoenzymatic Transformations in the Absence of Bulk Water: A More Natural Way of Using Enzymes

“…Owing to the large diversity of functional groups and linkages present in the three‐dimensional polymeric structure of lignin, dilignols such as 6 (Scheme ) are commonly used as model compounds, circumventing the challenges of analyzing the complex product mixtures obtained from the natural polymer. Weißbach et al.…”