Amination of biorefinery technical lignins using Mannich reaction synergy with subcritical ethanol depolymerization

Area of Science:

• Biomass Valorization
• Lignin Chemistry
• Organic Synthesis

Background:

• Biorefinery technical lignins require improved chemical activity for broader applications.
• Introducing functional groups, like amines, can enhance lignin's utility.
• Understanding lignin's structural transformations is key to unlocking its potential.

Purpose of the Study:

• To investigate the chemical structural changes in lignin during alcoholic depolymerization.
• To explore the introduction of amino groups into lignin via the Mannich reaction.
• To elucidate the reaction mechanisms and identify key factors influencing lignin reactivity.

Main Methods:

• Alcoholic depolymerization and Mannich reaction were employed.
• Gel Permeation Chromatography (GPC) and solution-state Nuclear Magnetic Resonance (NMR) spectroscopy were used for structural analysis.
• Elemental analysis quantified the introduced amine groups.

Main Results:

• Depolymerization, demethoxylation, and bond cleavage were observed during depolymerization.
• Depolymerization temperature, not capping reagents, significantly impacted lignin reactivity.
• The Mannich reaction showed high selectivity for specific positions (H3,5 and G5), with H units being more reactive.

Conclusions:

• Optimizing depolymerization temperature is crucial for enhancing lignin reactivity.
• The Mannich reaction offers a selective method for functionalizing lignin.
• Fundamental insights into lignin chemistry facilitate high-value biorefinery applications.