Acridinium Photoredox Catalysts for Selective Lignin C-O Bond Cleavage
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Solution Overview
Problem
Current methods for lignin depolymerization do not achieve selective C—O bond cleavage, resulting in complex mixtures of products, and existing photocatalysts require pre-oxidation steps, making them inefficient for producing bio-polyols from lignin.
Innovation Solution
Development of acridinium-based photoredox catalysts that facilitate oxidative C—O bond cleavage of lignin model compounds without a peroxidation step, using compounds of specific structures that can be synthesized under mild conditions and exhibit superior photoredox catalytic activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If classical strategies for lignin depolymerization (pyrolysis, hydrolysis, enzymolysis, hydrogenolysis, and oxidation) are used, then lignin can be broken down, but highly selective single aromatic building blocks cannot be produced due to complex mixtures of products
Solution Approach 1:
The patent modifies the chemical parameters of the oxidation process by using photoredox catalysis with specific catalysts (Ru(bpy)3Cl2, Ir(ppy)3, or organic dyes) under visible light irradiation. This changes the reaction pathway from conventional oxidation to photo-induced electron transfer, enabling selective C-O bond cleavage at the benzylic position while maintaining other lignin linkages intact, thus producing selective aromatic building blocks rather than complex mixtures
Solution Approach 2:
The patent introduces photoredox catalysts as intermediary substances that mediate the oxidation process. These catalysts absorb visible light and generate reactive species (radical cations or excited states) that selectively activate the C-O bond at the benzylic position. The catalyst acts as a mediator that enables selective bond cleavage without requiring harsh conditions that would lead to non-selective degradation and complex product mixtures
2Manufacturing precision
If photoredox catalysis is used for selective C-O bond cleavage of lignin β-O-4 model compounds, then selectivity is improved, but pre-oxidation of benzylic alcohols is required which adds process complexity
Solution Approach 1:
The patent eliminates the need for preliminary pre-oxidation steps by designing photoredox catalyst systems that can directly activate and cleave the C-O bond at the benzylic position in a single step. The photo-induced electron transfer mechanism allows the catalyst to directly interact with the substrate without requiring prior oxidation to carbonyl compounds, thus simplifying the overall process from multiple steps to a single selective transformation
Solution Approach 2:
The patent inverts the conventional oxidation approach by using photo-reduction mechanisms. Instead of using strong oxidants to pre-oxidize benzylic alcohols followed by C-O cleavage, the photoredox catalyst uses visible light to generate reducing equivalents that directly facilitate C-O bond breaking through single electron transfer, reversing the traditional oxidative pathway and eliminating intermediate steps
3Manufacturing precision
If cobalt deuteroporphyrin complex and Oxone are used for C-O bond cleavage to afford 1,2-diol derivatives, then the reaction can proceed, but expensive catalyst and high oxidant equivalents are required
Solution Approach 1:
The patent replaces expensive cobalt deuteroporphyrin complexes with cheaper, readily available photoredox catalysts such as Ru(bpy)3Cl2, Ir(ppy)3, or organic dyes that can be purchased at lower costs. These catalysts are used in catalytic amounts (typically 1-10 mol%) rather than the stoichiometric or near-stoichiometric amounts required by conventional methods, significantly reducing material costs while maintaining high selectivity for 1,2-diol derivative production
Solution Approach 2:
The patent changes the oxidant system from requiring 5 equivalents of Oxone to using molecular oxygen or air as the terminal oxidant in combination with photoredox catalysis. This parameter change reduces oxidant consumption from stoichiometric to catalytic amounts, lowering both material cost and waste generation while maintaining efficient C-O bond cleavage and 1,2-diol formation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The acridinium-based catalysts achieve high yields of 1,2-diol derivatives from lignin models, outperforming previous catalysts like the Fukuzumi catalyst, and enable efficient lignin depolymerization under mild conditions using visible light as an oxidant, suitable for producing bio-polyols.
Implementation Method 1
acridinium-based photoredox catalysts that facilitate oxidative C—O bond cleavage of lignin model compounds without a peroxidation step, using compounds of specific structures that can be synthesized under mild conditions and exhibit superior photoredox catalytic activity
Data Source
AI summary
The present invention belongs to the field of catalytic chemistry, and more specifically to catalysed oxidation of lignin. It also relates to synthesis of catalyst compounds.The present invention relates to new acridinium-based photoredox catalyst compounds and their use thereof in a chemical reaction, preferably in depolymerisation of lignin models and ultimately lignin. The invention also relates to the method of synthesis of the new acridinium-based photoredox catalyst compounds according to the invention.