Isotope labeling-based studies on the pyrolysis of dimeric β-O-4 lignin model compounds phenylethyl phenyl ether and phenylethanol phenyl ether

In this study, the pyrolysis of the β-O-4 lignin model compounds phenylethyl phenyl ether (PPE) and phenylethanol phenyl ether (PEPE) in the presence of H 2 O, D 2 O and H 2 18 O at 500°C was investigated. The pyrolysis products were examined by GC-MS to analyze the pyrolysis process and product formation mechanisms. By comparing the pyrolysis products of PPE and PEPE, the chemical structure effect of C α -OH was found to decrease the yield of styrene, benzaldehyde, and phenylethanol, while increasing the yield of acetophenone, which facilitated the decomposition of C β -O and led to an increase of the phenol yield. Analysis of the isotope-labeled PPE pyrolysis products revealed that phenol undergoes deuteration to varying degrees, and the deuterated intermediates undergo intramolecular exchanges to produce deuterium-substituted phenols (C 6 H 5 OD, C 6 H 4 DOH, C 6 H 4 DOD), which verified the presence of the reciprocal isomer 2,4-cyclohexadienone. The product acetophenone from the pyrolysis of PEPE was deuterated to varying degrees, indicating multiple pathways of formation, which was accompanied by the formation of phenol, resulting in a high abundance of acetophenone and phenol products. Phenylethanol was found to be an important intermediate in the formation of phenylacetaldehyde. The order of occurrence of the different reaction intermediates of PPE and PEPE was hypothesized and the free radical reaction was found to play a dominant role. This experiment reveals the evolution of the products of PPE and PEPE during pyrolysis. • Co-pyrolysis of PPE and PEPE was carried out using H 2 O, D 2 O and H 2 18 O as isotopic labels to study the pyrolysis mechanism of PPE and PEPE and the evolution of the pyrolysis products. • The generation sequence of various reaction intermediates of PPE and PEPE was discovered, and radical reactions play a dominant role. • The pyrolysis reaction mainly occurred on the side chain of the benzene ring according to the fragment ion peaks of the products and the formation mechanisms of the products during pyrolysis were revealed by isotope labeling. • This study can provide reference for the research on the pyrolysis mechanism of lignin.