Naphthalene Structures Derived from Lignins During Phenolation

Abstract

Phenolation is a commonly used method to improve the reactivity of lignin for various applications. In this study, resinol lignin models (syringaresinol and pinoresinol) and eucalyptus alkali lignin were treated under acid-catalyzed phenolation conditions to investigate the products derived from resinol (ββ) structures of lignins. The phenolation products were characterized by means of GC-MS and NMR spectroscopy following separation using flash chromatography and thin-layer chromatography. A series of new naphthalene products were identified from phenolation of syringaresinol, and the corresponding guaiacyl analogs were also identified by GC-MS. The C1À Cα bond of these resinol compounds was cleaved to release syringol or guaiacol during phenolation. In addition, diphenylmethane products formed from phenol or phenol and syringol/ guaiacol were found in the phenolation products. Comparatively, more naphthalene products were obtained by phenolation from syringaresinol than those obtained from pinoresinol. HSQC NMR characterization of the phenolated alkali lignin revealed that naphthalene structures formed in the phenolated lignin.

Revealing the Structural Influence on Lignin Phenolation and Its Nanoparticle Fabrication with Tunable Sizes

“…Lignin Phenolation. Phenolation was performed according to the procedure as previously reported, 43 and the L/P ratio and reaction temperature were studied. In short, 100 mg of lignin was dissolved in 100−400 mg of phenol.…”

Lignin to value-added chemicals and advanced materials: extraction, degradation, and functionalization

“…8). 147–149 The phenol/lignin ratio, acid charge, and reaction temperature have a significant effect on the degree of phenolation. 147,150 When phenolation of Klason lignin was performed using the microwave heating method, the phenolation rate increased with a higher phenol/lignin ratio.…”

Efficient Synthesis of Pinoresinol, an Important Lignin Dimeric Model Compound

“…Pinoresinol structures with a β-β ′ -linkage between two monolignols are important structures in the lignins from softwoods, dicots, and monocots, especially in some technical lignins from hardwood (Yue et al, 2012b;Li et al, 2020). Not only do they affect the lignification pathway, but also have implications for the biorefinery.…”

“…Because of its wide range of bioactivities and its chemical structure related to lignin, pinoresinol and its lignan analog play very important roles in pharmaceutical research, lignin biosynthesis, and other related studies (Umezawa, 2003;Zhang et al, 2003;Jung et al, 2006;Ralph et al, 2008;Yue et al, 2012a;Tamura et al, 2014). Moreover, substantial amounts of resinol (β-β ′ ) structures, including pinoresinol and syringaresinol, remained and can be identified in several technical lignins, which is crucial to the phenolation of alkaline lignin, for example (Li et al, 2020;Zhao et al, 2020). Studies on the biosynthesis of pinoresinol structures in lignin, technical lignin modifications, pinoresinol-related lignans, and pinoresinol contributions to a healthy human diet or for disease prevention require easy access to pinoresinol.…”