Depolymerizing Lignin

Lignin, a component in the cell walls of plants, makes up almost 30% of all the organic carbon on Earth. But because the aromatic biopolymer is notoriously recalcitrant, it’s usually treated as a waste product of the paper and pulp industry and burned, sending all those valuable aromatics up in flames. Now, Shannon S. Stahl and colleagues at the University of Wisconsin, Madison, have come up with a way to depolymerize lignin into low-molecular-mass aromatics, with a yield of 60% by weight(Nature 2014, DOI: 10.1038/nature13867). The process (shown) begins by oxidizing key benzylic alcohols in the lignin backbone. This step renders nearby β-ether linkages prone to cleavage during a subsequent treatment with aqueous formic acid and sodium formate at 110 °C. The researchers use the procedure to break down lignin from aspen trees. “The overall yield of structurally identified, monomeric aromatics obtained here is the highest reported so far for lignin depolymerization,” note the chemists. “Although some of the products obtained from this process have direct commercial value, the more important result may be the generation of a stream of soluble aromatic feedstocks for further upgrading.”