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Directly Microwave‐Accelerated Cleavage of C−C and C−O Bonds of Lignin by Copper Oxide and H 2 O 2
Author(s) -
Qu Chen,
Ito Keigo,
Katsuyama Isamu,
Mitani Tomohiko,
Kashimura Keiichiro,
Watanabe Takashi
Publication year - 2020
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.202000502
Subject(s) - guaiacol , vanillic acid , chemistry , vanillin , bond cleavage , dimer , photochemistry , lignin , organic chemistry , catalysis
Model erythro, phenolic, and nonphenolic lignin β‐O‐4 dimer compounds are treated with copper oxide and H 2 O 2 at the electronic field maximum position of a single‐mode 2.45 GHz microwave system equipped with a cavity resonator. The products obtained through microwave heating and oil‐bath heating with the same reaction vessel and temperature profile are quantitatively compared. Dimer degradation is found to proceed through consecutive elementary reactions. The phenolic dimer is dehydroxylated and this is followed by the spontaneous cleavage of C α −C β and C−O−C bonds to produce guaiacol, vanillin, and vanillic acid. The reaction of the nonphenolic dimer produces veratric acid, veratraldehyde, and guaiacol. Microwave irradiation accelerates cleavage of the side chain and the oxidation of vanillin to vanillic acid. However, no acceleration of veratraldehyde oxidation to veratric acid or aromatic ring cleavage to produce dicarboxylic acids is observed. The selective acceleration of elementary reactions during the degradation of model lignin compounds indicates that microwaves interact with reaction intermediates that are sensitive to electromagnetic waves.