Ruthenium ion catalysed C-C bond activation in lignin model compounds - towards lignin depolymerisation

Area of Science:

• Chemical Engineering
• Organic Chemistry
• Catalysis

Background:

• Lignin is an abundant renewable feedstock for aromatic chemicals.
• Depolymerizing lignin requires breaking C-O and C-C inter-unit linkages.
• Effective methods for cleaving recalcitrant C-C linkages in lignin are limited.

Purpose of the Study:

• To develop an effective method for activating and converting recalcitrant C-C linkages in lignin.
• To investigate a ruthenium ion-catalyzed oxidative methodology for lignin depolymerization.

Main Methods:

• Utilized a ruthenium-catalyzed oxidative methodology (RICO) on biphenyl as a model compound.
• Employed DFT calculations to understand the reaction mechanism.
• Applied RICO to a lignin model hexamer containing β-5, 5-5', and β-O-4 linkages.
• Analyzed reaction products using 1H, 13C NMR, GC-MS, GPC, and 2D NMR spectroscopy (HSQC, HMBC, 31P NMR).

Main Results:

• Achieved 30% conversion of biphenyl's 5-5' C-C linkage with 75% selectivity towards benzoic acid.
• Demonstrated the first oxidative activation of the biphenyl inter-ring C-C bond.
• Converted >90% of 5-5' linkages and >80% of β-5 linkages in a lignin model hexamer within 30 minutes.
• Reported the first successful conversion of the 5-5' linkage in a lignin model hexamer.

Conclusions:

• The ruthenium ion-catalyzed oxidative methodology is effective for activating and converting recalcitrant C-C linkages in lignin.
• This approach offers a promising route for the valorization of lignin into aromatic chemicals.
• The study presents a novel method for lignin depolymerization, addressing a key challenge in the field.