Co(salen)-catalyzed oxidation of lignin models to form benzoquinones and benzaldehydes: A computational and experimental studyAuthor(s): Connor J. Cooper; Shahrina Alam; Vincent de Paul N. Nziko; Ryne C. Johnston; Alexander S. Ivanov; Zhongyu Mou; David B. Turpin; Alan W. Rudie; Thomas J. Elder; Joseph J. Bozell; Jerry M. Parks
Source: ACS Sustainable Chemistry & Engineering
Publication Series: Scientific Journal (JRNL)
Station: Southern Research Station
Download Publication (2.0 MB)
DescriptionLignin is a highly abundant polyphenolic polymer that imparts mechanical strength to plant biomass. Transition-metal complexes can catalyze lignin oxidation to produce value-added products, but low catalytic efficiency has hampered their use in industry. Identifying the chemical and structural factors that govern catalytic activity is a prerequisite to rational design of catalysts with improved activity. Here, we combine computational and experimental approaches to investigate the mechanism of Co(salen)-catalyzed oxidation of the monomeric lignin models syringyl (S), vanillyl (G), and 4-hydroxybenzyl alcohol (H) to produce benzoquinone and benzaldehyde products. Experimentally, S oxidation to form dimethoxybenzoquinone proceeded efficiently with a Co(salen) catalyst coordinated by a pyridine ligand, but G and H did not undergo oxidation. Density functional theory calculations reveal that catalyst regeneration is energetically unfavorable in the presence of H, which prevents oxidation. In contrast, S readily facilitates catalyst regeneration. Formation of methoxybenzoquinone from G was achieved experimentally by adding bulky, noncoordinating bases. These findings provide a fundamental baseline for enhancing the activity of Co-Schiff base catalysts toward lignin-like molecules by adding sterically hindered nitrogenous bases or potentially by including a cocatalyst that promotes catalyst regeneration.
- You may send email to email@example.com to request a hard copy of this publication.
- (Please specify exactly which publication you are requesting and your mailing address.)
CitationCooper, Connor J.; Alam, Shahrina; Nziko, Vincent de Paul N.; Johnston, Ryne C.; Ivanov, Alexander S.; Mou, Zhongyu; Turpin, David B.; Rudie, Alan W.; Elder, Thomas J.; Bozell, Joseph J.; Parks, Jerry M. 2020. Co(salen)-catalyzed oxidation of lignin models to form benzoquinones and benzaldehydes: A computational and experimental study. ACS Sustainable Chemistry & Engineering. 8(18): 7225-7234. https://doi.org/10.1021/acssuschemeng.0c01970.
Keywordsshiff base, valorization, biomass, transition metal, density functional theory, catalysis
- Deactivation of Co-Schiff base catalysts in the oxidation of para -substituted lignin models for the production of benzoquinones
- Steric effects of bulky tethered arylpiperazines on the reactivity of Co-Schiff base oxidation catalysts—a synthetic and computational study
- Steric effects in the design of Co-Schiff base complexes for the catalytic oxidation of lignin models to para-benzoquinones
XML: View XML