Synthesis of 2,6‐Dimethoxy‐p‐aminophenol from Hardwood Lignin

From the hardwood: A route was developed to transform hardwood lignin toward 2,6-dimethoxy-p-aminophenol with high yield and keeping the inherent functional groups. Lignin was first oxidized to syringaldehyde, which was converted toward 2,6-dimethoxy-p-aminophenol via oxidation, oximation, and hydrogenation. The presence of the methoxy group guaranteed the high selectivity.

Abstract

Although the multiple functional groups in biomass offer notable chances for producing high-value chemicals, most of the current studies focused on the (deep) defunctionalization of biomass and its derivates. Herein, we present a catalytic approach to valorize birch wood lignin with maintaining the methoxy and hydroxy groups in the final product (i. e., 2,6-dimethoxy-p-aminophenol), which has applications in different sectors such as pharmaceuticals. The proved approach involves four steps with a high yield (19.8 wt % on the basis of used lignin) to 2,6-dimethoxy-p-aminophenol. The native lignin in birch wood was first converted using alkaline aerobic oxidation in the presence of copper ions toward high-yield syringaldehyde, which was then selectively oxidized toward 2,6-dimethoxy-1,4-benzoquinone using H₂O₂ and V₂O₅. Oximation of 2,6-dimethoxy-1,4-benzoquinone can selectively form 2,6-dimethoxy-1,4-benzoquinone-4-oxime, which can be quantitatively hydrogenated toward 2,6-dimethoxy-p-aminophenol. This work highlights the unique potential of biomass and its derivates for the sustainable production of high-value products with exploring the value of inherent functional groups.

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