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Mild Heterogeneous Palladium‐Catalyzed Cleavage of β‐ O ‐4′‐Ether Linkages of Lignin Model Compounds and Native Lignin in Air
Author(s) -
Galkin Maxim V.,
Sawadjoon Supaporn,
Rohde Volker,
Dawange Monali,
Samec Joseph S. M.
Publication year - 2014
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201300540
Subject(s) - palladium , depolymerization , chemistry , lignin , ketone , catalysis , ether , bond cleavage , organic chemistry , aryl , polymer chemistry , alkyl
A mild and robust heterogeneous palladium‐catalyzed CO bond cleavage of 2‐aryloxy‐1‐arylethanols using formic acid as reducing agent in air was developed. The cleaved products were isolated in 92–98 % yield; and by slightly varying the reaction conditions, a ketone, an alcohol, or an alkane can be generated in near‐quantitative yield. This reaction is applicable to cleaving the β‐ O ‐4′‐ether bond found in lignin polymers of different origin. The reaction was performed on a lignin polymer model to generate either the monomeric aryl ketone or alkane in a quantitative yield. Moderate depolymerization was achieved with native lignin at similar reaction conditions. Mechanistic studies under kinetic control indicate that an initial palladium‐catalyzed dehydrogenation of the alcohol is followed by insertion of palladium to an enol equivalent. A palladium–formato complex reductively cleaves the palladium–enolate complex to generate the ketone.