Successful selective production of vanillic acid from depolymerized sulfite lignin and its application to poly(ethylene vanillate) synthesis.

Towards lignin upgrading, vanillic acid (VA), a lignin-derived guaiacyl compound, was produced from sulfite lignin for successfully synthesizing poly(ethylene vanillate), an aromatic polymer. The engineered Sphingobium sp. SYK-6-based strain in which the genes responsible for VA/3-O-methyl gallic acid O-demethylase and syringic acid O-demethylase were disrupted was able to produce vanillic acid (VA) from the mixture consisting of acetovanillone, vanillin, VA, and other low-molecular-weight aromatics obtained by Cu(OH) ₂ -catalyzed alkaline depolymerization of sulfite lignin and membrane fractionation. From the bio-based VA, methyl-4-(2-hydroxyethoxy)-3-methoxybenzoate was synthesized via methylesterification, hydroxyethylation, and distillation, and then it was subjected to polymerization catalyzed by titanium tetraisopropoxide. The molecular weight of the obtained poly(ethylene vanillate) was evaluated to be M _w  = 13,000 (M _w /M _n  = 1.99) and its melting point was 261 °C. The present work proved that poly(ethylene vanillate) is able to be synthesized using VA produced from lignin for the first time.
Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Tomonori Sonoki reports financial support was provided by Japan Science and Technology Agency. Yudai Higuchi reports financial support was provided by Japan Science and Technology Agency. Yudai Higuchi reports financial support was provided by Hirosaki University. Hiroya Ishimaru reports financial support was provided by Japan Science and Technology Agency. Takuya Yoshikawa reports financial support was provided by Japan Science and Technology Agency. Takao Masuda reports financial support was provided by Japan Science and Technology Agency. Chiho Sakamoto reports financial support was provided by Japan Science and Technology Agency. Naofumi Kamimura reports financial support was provided by Japan Science and Technology Agency. Eiji Masai reports financial support was provided by Japan Science and Technology Agency. Daisuke Takeuchi reports financial support was provided by Japan Science and Technology Agency.
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