Isolation of Functionalized Phenolic Monomers through Selective Oxidation and CO Bond Cleavage of the β‐O‐4 Linkages in Lignin

Abstract

Functionalized phenolic monomers have been generated and isolated from an organosolv lignin through a two-step depolymerization process. Chemoselective catalytic oxidation of b-O-4 linkages promoted by the DDQ/tBuONO/ O 2 system was achieved in model compounds, including polymeric models and in real lignin. The oxidized b-O-4 linkages were then cleaved on reaction with zinc. Compared to many existing methods, this protocol, which can be achieved in one pot, is highly selective, giving rise to a simple mixture of products that can be readily purified to give pure compounds. The functionality present in these products makes them potentially valuable building blocks.

Complete lignocellulose conversion with integrated catalyst recycling yielding valuable aromatics and fuels

“…Based on model compound studies (Supplementary Note 2) we propose that depolymerization proceeds via scission of the β -O-4 linkage through a series of dehydrogenation, hydrogenolysis and hydrogenation events involving a ketone intermediate 22 . This is in agreement with existing two-step methods that achieve efficient depolymerization of organosolv lignin to aromatics through selective pre-oxidation followed by reductive cleavage 10,12 .…”

“…Moreover, under these processing conditions the lignin component is structurally modified, rendering its further catalytic valorization very challenging [4][5][6][7] . This remains true despite impressive advances in the selective conversion of lignin model compounds 8,9 and depolymerization of organosolv lignin [10][11][12][13][14] . Recently, elegant research has focused on lignocellulose fractionation in the presence of a catalyst 4,[15][16][17] .…”

Investigation of the Chemocatalytic and Biocatalytic Valorization of a Range of Different Lignin Preparations: The Importance of β-O-4 Content

“…21,22 Oak hardwood was treated with dioxane/H2O (9:1) containing 0.2 M HCl for 1 hr under reflux, to give an organosolv lignin, 6 and a standard organosolv method was used to prepare lignin from eucalyptus, which was compared with autohydrolysis lignin and Kraft lignin also from eucalyptus. Lignin was also prepared using ionic liquid triethylammonium hydrogen sulfate…”

“…1,2 Several new chemocatalytic approaches for lignin valorisation have been published in recent years, that are able to generate aromatic monomers from lignin feedstocks. [3][4][5][6][7][8][9] There is also renewed interested in novel microbial enzymes for lignin oxidation, 10 and the use of engineered microbial hosts for the generation of aromatic products via microbial biotransformation. [11][12][13][14] A complicating factor in the field is that there are a number of different methods for the fractionation of lignocellulose that generate lignin preparations of very different structure, physical…”

Identification of an extracellular bacterial flavoenzyme that can prevent re-polymerisation of lignin fragments

“…The valorisation of lignin to produce aromatic chemicals is an important problem in the design of a future biorefinery for production of fuels and chemicals from renewable sources [1], and several new approaches involving either chemocatalysis [2][3][4][5][6] or biocatalysis [7][8][9][10] have been published in recent years.…”