1 research outputs found
Selective C–C Bond Cleavage of Methylene-Linked Lignin Models and Kraft Lignin
Biorefinery
and paper pulping lignins, referred hereto as technical
lignins, contain condensed C–C interunit linkages. These robust
C–C linkages with higher bond dissociation energies are difficult
to disrupt under hydrogenolysis conditions, which are generally used
for cleaving C–O bonds of native lignin in biomass or model
C–O linked compounds. Thus, selective interunit C–C
cleavage to release aromatic monomers for high-value applications
is a challenge. We report an effective catalytic system to cleave
such C–C bonds selectively under mild conditions. A representative
methylene-linked C–C model dimer achieves 88% yield of mainly
two aromatic monomers within 1.5 h at a reasonably low temperature
(250 °C) using a commercial CoS<sub>2</sub> catalyst. Aromatic
monomers convert to nonaromatic products upon the reaction for a prolonged
time. The interunit C–C bond of the dimer become unreactive
to cleavage upon dehydroxylation of aromatic rings, while the methoxyl
group has little effect on the cleavage. β-1 and 5-5 C–C
linked model dimers formed demethoxylated hydroxyl dimers as the major
products. Depolymerization of a purified kraft lignin fraction yields
five aromatic monomers and lower-molecular-weight soluble products.
This study opens up the possibility of valorization of technical lignins
using inexpensive catalysts