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<p>Hydrogenolysis of lignin generates a portfolio of products, the yields of which are generally calculated using a subset of phenolic monomers that are dependent on the lignin composition, product distribution, and analytical technique. Some lignins are naturally γ-acylated; poplar lignins, for example, have <i>p</i>-hydroxybenzoate groups on 1–15% of their syringyl subunits. Upon hydrogenolysis, it is generally assumed that the <i>p</i>-hydroxybenzoate is cleaved before the deacylated lignin is depolymerized. Hydrogenolysis of model γ-<i>p</i>-hydroxybenzoylated β-aryl ethers do not, however, produce the deacylated β-aryl ether intermediates, as was previously conjectured; products instead derive from palladium-assisted reactions on the cinnamyl <i>p</i>-hydroxybenzoates resulting in initial β-ether cleavage. The <i>p</i>-hydroxybenzoate moiety itself also undergoes carboxylate-assisted palladium-catalyzed C–H bond activation to form the 2,4-dihydroxybenzoate, that subsequently converts to the 2,4-dihydroxycyclohex-1-enoate. These details underscore previously unrecognized pathways and products that are key to understanding the different hydrogenolysis product distributions from naturally acylated lignins that are prevalent biomass-conversion feedstocks.</p>

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Pd/C promotes C–H bond activation and oxidation of p-hydroxybenzoate during hydrogenolysis of poplar

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年6月6日

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  • Canan Sener,
  • Vitaliy I. Timokhin,
  • Jan Hellinger,
  • John Ralph,
  • Steven D. Karlen

摘要

Hydrogenolysis of lignin generates a portfolio of products, the yields of which are generally calculated using a subset of phenolic monomers that are dependent on the lignin composition, product distribution, and analytical technique. Some lignins are naturally γ-acylated; poplar lignins, for example, have p-hydroxybenzoate groups on 1–15% of their syringyl subunits. Upon hydrogenolysis, it is generally assumed that the p-hydroxybenzoate is cleaved before the deacylated lignin is depolymerized. Hydrogenolysis of model γ-p-hydroxybenzoylated β-aryl ethers do not, however, produce the deacylated β-aryl ether intermediates, as was previously conjectured; products instead derive from palladium-assisted reactions on the cinnamyl p-hydroxybenzoates resulting in initial β-ether cleavage. The p-hydroxybenzoate moiety itself also undergoes carboxylate-assisted palladium-catalyzed C–H bond activation to form the 2,4-dihydroxybenzoate, that subsequently converts to the 2,4-dihydroxycyclohex-1-enoate. These details underscore previously unrecognized pathways and products that are key to understanding the different hydrogenolysis product distributions from naturally acylated lignins that are prevalent biomass-conversion feedstocks.