25. Selectively Upgrading Lignin Derivatives to Carboxylates through Electrochemical Oxidative C(OH)−C Bond Cleavage by a Mn-Doped Cobalt Oxyhydroxide Catalyst

Zhou, H., Li, Z., Xu, S. M., Lu, L., Xu, M., Ji, K., Ge, R., Yan, Y., Ma, L., Kong, X., Zheng, L., Duan, H.*
Angew. Chem. Int. Ed. 2021, 60(16), 8976–8982
DOI: 10.1002/anie.202015431

Abstract
Oxidative cleavage of C(OH)−C bonds to afford carboxylates is of significant importance for the petrochemical industry and biomass valorization. Here we report an efficient electrochemical strategy for the selective upgrading of lignin derivatives to carboxylates by a manganese-doped cobalt oxyhydroxide (MnCoOOH) catalyst. A wide range of lignin-derived substrates with C(OH)-C or C(O)-C units undergo efficient cleavage to corresponding carboxylates in excellent yields (80–99 %) and operational stability (200 h). Detailed investigations reveal a tandem oxidation mechanism that base from the electrolyte converts secondary alcohols and their derived ketones to reactive nucleophiles, which are oxidized by electrophilic oxygen species on MnCoOOH from water. As proof of concept, this approach was applied to upgrade lignin derivatives with C(OH)-C or C(O)-C motifs, achieving convergent transformation of lignin-derived mixtures to benzoate and KA oil to adipate with 91.5 % and 64.2 % yields, respectively.