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

[Display omitted] •The metabolic pathway of Sphigobium sp. SYK-6 was used to produce vanillic acid.•Vanillic acid was selectively produced from the depolymerized sulfite lignin.•The lignin-derived vanillic acid was subjected to poly(ethylene vanillate) synthesis.•The lignin-derived vanillic acid-based polymer was successfully synthesized.•Due to the subgram scale demonstration of the polymer synthesis, the yield was 23%. 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 Mw = 13,000 (Mw/Mn = 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.