Promising bulk production of a potentially benign bisphenol A replacement from a hardwood lignin platform

A full lignin-to-chemicals valorisation chain - from hardwood over bissyringols to aromatic polyesters (APEs) - is established for renewable 4-n-propylsyringol (PS), the main product from catalytic hydrogenolysis of (native) hardwood lignin. To do so, reagent-grade PS was produced from birch wood via reductive catalytic fractionation (RCF) and isolated in 34 wt% yield on lignin basis. Additional early-stage theoretical calculations, based on both relative volatility (a) and distillation resistance (Omega) as well as Aspen Plus (R) simulations, predict that the isolation of PS by means of distillation is economically feasible at industrial scales ($85-95 per ton of propylphenolics at 200-400 kt a(-1) scale). Subsequent stoichiometric acid-catalysed condensation with formaldehyde unveils a remarkably high 92 wt% selectivity towards the dimer 3,3'-methylenebis(4-n-propylsyringol) (m,m'-BSF-4P), which is isolated in >99% purity by facile single-step crystallisation. The striking dimer selectivity is ascribed to the synergetic interplay between the activating methoxy groups and the oligomerisation-inhibiting propyl chain. Next, an in vitro human oestrogen receptor a (hERa) assay was performed to ensure safe(r) chemical design. The bissyringyl scaffold displays reduced potency (similar to 19-45-times lower affinity than bisphenol A) and lower efficacy (similar to 36-45% of BPA's maximum activity). Lastly, to assess the functionality of the safe(r) bissyringol scaffold, it was converted into an APE. The APE displays a M-w = 43.0 kDa, M-n = 24.4 kDa, T-g = 157 degrees C and T-d,T-5% = 345 degrees C. In short, (i) the feasibility and scalability of the feedstock, (ii) the simplified process conditions, (iii) the reduced in vitro oestrogenicity, and (iv) the functionality towards polymerisation, make this bissyringol a renewable and potentially benign bisphenol replacement, capable for production at bulk scale.