Theoretical studies on pyrolysis mechanism of guaiacol as lignin model compound

The pyrolysis processes of guaiacol as lignin model compound were theoretically investigated by using density functional theory methods at B3LYP/6-31G++(d,p) level. The bond dissociation enthalpies (BDE) of the major bonds of guaiacol were calculated. Three possible pyrolytic pathways were proposed according to related experimental results, calculation results of BDE of guaiacol and research experiences. The standard kinetic parameters in each reaction pathway were calculated. In reaction pathway (1), the initial reaction step of guaiacol pyrolysis is the homolytic cleavage of the CH3-O bond and 1,2-dihydroxybenzene is the main pyrolysis product, of which the total energy barrier of formation is 312.9 kJ/mol. In reaction pathway (2), the initial reaction step of guaiacol pyrolysis is the homolytic cleavage of the O-H bond and the main pyrolysis products are o-cresol, 2-hydroxybenzaldehyde, o-quinonemethide, of which the total energy barrier of formation is 474.1 kJ/mol. In reaction pathway (3), addition o...