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ChemSusChem. 2020 Mar 23. doi: 10.1002/cssc.202000753. [Epub ahead of print]

Mechanistic study of diaryl ether bond cleavage during palladium-catalyzed lignin hydrogenolysis.

Author information

1
Massachusetts Institute of Technology, Department of Chemical Engineering, 32 Vassar St, 02139, Cambridge, UNITED STATES.
2
University of Wisconsin Madison, Biochemistry, UNITED STATES.
3
University of Wisconsin Madison, Chemical and Biological Engineering, UNITED STATES.
4
Ecole Polytechnique Federale de Lausanne, Institute of Chemical Sciences and Engineering, SWITZERLAND.
5
University of Wisconsin Madison, Chemistry, UNITED STATES.
6
University of Wisconsin-Madison, Biochemistry, The Wisconsin Energy Institute, 1552 University Ave, WI 53726-4084, Madison, UNITED STATES.

Abstract

Hydrogenolysis has emerged as one of the most effective means of converting polymeric lignin into monoaromatic fragments of value. Reported yields may be higher than for other methods and can exceed the theoretical yields estimated from measures of the content of lignin's most readily cleaved alkyl-aryl ether bonds in β-ether units. The high yields suggest that other units in lignin are being cleaved. Diaryl ether units are important units in lignin, and their cleavage has been examined previously using simple model compounds, such as diphenyl ether. Herein, we analyze the hydrogenolysis of model compounds that closely resemble the native lignin 4-O-5 diaryl ether units. The results provide unexpected insights into the reactivity and partial cleavage of these compounds. The models and lignin polymer produce not only monomers, but also unusual 1,3,5-meta-substituted aromatics that appear to be diagnostic for the presence and the cleavage of the 4-O-5 diaryl ether unit in lignin.

KEYWORDS:

biorefinery; catalysis; diaryl ether; lignin model compound; reaction mechanism

PMID:
32202385
DOI:
10.1002/cssc.202000753

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