Theoretic studies on decomposition mechanism of o-methoxy phenethyl phenyl ether: Primary and secondary reactions

• The pyrolysis of o-CH3O-PPE as lignin model compound was investigated.
• The substituent effect of methoxy group on BDE of β-O-4 linkage was investigated.
• Several possible pyrolytic reaction pathways (free radical and concerted reactions) were proposed.
• Secondary reactions were investigated.

In order to understand the pyrolysis mechanism of lignin and identify the chemical pathways for the formation of main products during pyrolysis, the primary and secondary reactions of o-methoxy phenethyl phenyl (o-CH3O-PPE) pyrolysis are investigated by DFT method at (M06-2X)/6-31G+ (d,p) level. It is found that the o-methoxy group reduces the bond dissociation energies (BDEs) of CβO and C(aromatic)O bonds of the β-O-4 linkage. Kinetic analysis results support the concerted reaction pathway 12 as the major primary reaction channel which leads to the formation of guaiacol and styrene. Salicylaldehyde is arisen from the secondary pyrolysis of guaiacol via bimolecular reaction at higher temperature.