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 1H nuclear magnetic resonance spectroscopy (1H-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.