Analytical Pyrolysis Pathways of Guaiacyl Glycerol-β-guaiacyl Ether by Py-GC/MS

Abstract

A synthetic method for obtaining a lignin model compound of β-O-4 structure, guaiacyl glycerol-β-guaiacyl ether, was researched through five reaction steps from guaiacol. The key step of this synthetic method was the condensation reaction between 4-(α-bromoacetyl)-guaiacol (III) and guaiacol (I). The compounds were characterized by 1 H nuclear magnetic resonance spectroscopy ( 1 H-NMR) and two-dimensional nuclear magnetic resonance (2D-NMR). Pyrolysis behaviors of guaiacyl glycerol-β-guaiacyl ether were investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The thermal behavior and the evolution profiles of major volatile fragments from the guaiacyl glycerol-β-guaiacyl ether pyrolysis were evaluated. Guaiacol is the major product through Cβ-O homolysis at low temperatures. Cβ-O homolysis and Cβ-O concerted decomposition occurred at moderate temperatures, producing guaiacol, 2-hydroxybenzaldehyde, 2-methoxybenzaldehyde, and various phenolic compounds. At high temperatures, the products obtained from Cβ-O homolysis and Cβ-O concerted decomposition experienced secondary thermal cracking, generating a large number of small molecule products, which increased the complexity of the pyrolytic products.

An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: a mechanistic study

“…Guaiacylglycerol-β-guaiacyl ether (GG) was synthesized and provided by Dr Gaojin Lyu with ∼99% purity, as determined by NMR. 30…”

Isolation, Characterization, and Depolymerization of l‐Cysteine Substituted Eucalyptus Lignin

“…Model compounds guaiacyglycerol‐β‐guaiacyl ether (GG, β‐O‐4), syringylglycerol‐β‐syringyl ether (SS, β‐O‐4), and benzylated glycerol‐β‐(4‐methyl syringal) aryl ether (GS, β‐O‐4) were synthesized as previously described. [ 48 ]…”

“…Synthesis of Lignin Model Compound: Model compounds guaiacyglycerol-β-guaiacyl ether (GG, β-O-4), syringylglycerol-β-syringyl ether (SS, β-O-4), and benzylated glycerol-β-(4-methyl syringal) aryl ether (GS, β-O-4) were synthesized as previously described. [48] L-Cysteine-Assisted Two-Step Acid/Alkali Treatment of GG, SS, or GS Model Compound: GG (30 mg, 93.75 µmol), SS (30 mg, 78.92 µmol) or GS (30 mg, 66.05 µmol) β-O-4 model compound was added into a 25 mL glass vial with 500 µL of 1,4-dioxane, and then 10 mL dilute acid stock solution (prepared by l-cysteine hydrochloride monohydrate (13.17 g, 74.99 mmol) and HCl (2.08 mL of 37% HCl) added to 500 mL deionized water) was added to the glass vial. For the control experiment without l-cysteine, 10 mL of HCl (0.2 mol L −1 ) was added.…”

Analytical Pyrolysis Characteristics of Enzymatic/Mild Acidolysis Lignin (EMAL)

“…(Table 4). Nevertheless, those alkyls or alkoxylated phenols that with complex side chains may undergo secondary cracking at high temperatures to produce simpler aromatic compounds such as H-phenols or aromatic hydrocarbons (Lou et al 2018;Liu et al 2016). For example, at 350 °C, the yield of 2-methoxy-4-vinylphenol was highest, and then decreased as the temperature increased, which may because of its poorer thermal stability, with secondary pyrolysis occurring at elevated temperatures.…”