Synthesis and Computational Investigation of Antioxidants Prepared by Oxidative Depolymerization of Lignin and Aldol Condensation of Aromatic Aldehydes.

Novel antioxidants are synthesized by CuSO4 -catalyzed oxidative depolymerization of lignin to form aromatic aldehydes followed by aldol condensation with methyl ethyl ketone (MEK). Aldol condensation greatly improves the antioxidation ability of lignin depolymerized products. Three lignin monomeric aromatic aldehydes, - p-hydroxybenzaldehyde, vanillin, and syringaldehyde - are further employed for aldol condensation with MEK, resulting in successful synthesis of new antioxidants 1-(4-hydroxyphenyl)pent-1-en-3-one (HPPEO), 1-(4-hydroxy-3-methoxyphenyl)pent-1-en-3-one (HMPPEO), and 1-(4-hydroxy-3,5-dimethoxyphenyl)pent-1-en-3-one (HDMPPEO), respectively. Kinetic modeling illustrates that p-hydroxybenzaldehyde has the highest rate of reaction with MEK, followed by vanillin and then syringaldehyde, which is probably affected by the presence of methoxy groups. The syringaldehyde-derived product (HDMPPEO) displays the best antioxidation ability. As revealed by density functional theory calculations, electron-donating groups, such as methoxy, and conjugated side chains effectively improve the antioxidation ability. A hydrogen atom transfer (HAT) mechanism tends to occur in nonpolar solvents, whereas a sequential proton-loss electron transfer (SPLET) mechanism is favored in polar solvents. This work thus can inspire new pathways for valorization of lignin to produce high value-added products.

Light-driven lignocellulosic biomass conversion for production of energy and chemicals.

The depletion of fossil fuels and the increasingly severe environmental pollution caused by massive fossil fuel consumption has driven the quick development of emerging renewable energy technologies. As the most extensive renewable carbon resource, lignocellulose is the potential substitute of fossil resources because of its sustainability and carbon-neutral features. Efficient lignocellulose conversion based on photocatalysis is a promising topic because of sustainable solar energy and the mild condition. This review highlights state-of-the-art photocatalytic technologies for lignocellulosic biomass conversion, focusing on the electricity generation, hydrogen production, and high-value-added biomass derivatives production. Moreover, the progress, challenge, and perspectives of related photocatalytic technologies are specifically discussed. It is recommended that developing more robust and efficient photocatalysts suitable for the complex structure of lignocellulose is necessary to promote the oxidation the biomass. Design and development of novel photochemical reactors and photoelectrochemical cells are also important for demonstration of light-driven lignocellulose conversion at larger scale.