Efficient cleavage of CC bonds in lignin using tetrabutylammonium tetrafluoroborate as both the catalyst and auxiliary electrolyte.

Lignin is a promising alternative to fossil resources due to its abundance of benzene ring monomers. However, the stability of the CC bond in lignin has hindered its efficient depolymerization. Electrochemical methods for breaking this bond are not well-studied. This paper presents a novel approach for catalytic depolymerization of lignin to produce acetals under mild conditions, without the need for additional catalysts. Under room temperature and in an air atmosphere, the combination of tetrabutylammonium tetrafluoroborate (TBABF) as an auxiliary electrolyte and methanol (MeOH) as a solvent has shown high selectivity in catalyzing the cleavage of CC bonds in lignin. Over 90.0 % of the resulting products are acetals, with the optimal conditions being a substrate concentration of 0.02 M, TBABF concentration of 0.008 M, a constant current of 30 mA, and a reaction time of 3 h. This led to a substrate conversion rate of 95.8 % and a product yield of 98.0 % for benzaldehyde dimethyl acetal (Bda). The mechanism study reveals that the tributyl ammonium radical cation decomposed by TBABF is adsorbed on the electrode surface. Subsequently, the adsorbed O is activated to form superoxide anion radical active species through single electron transfer, which plays a crucial catalytic role. TBABF acts as both an auxiliary electrolyte and a catalyst in this process. This research introduces a novel approach for electrocatalytic depolymerization of inert CC bonds in lignin, leading to the selective conversion into acetal chemicals.