Exploring the pyrolytic behavior of the lignin model compound α-hydroxy phenethyl phenyl

Lignin is the third most abundant biomass component, after cellulose and hemicellulose, although it receives less attention because of its complex polymeric structure and resistance to degradation. However, it is rich in aromatic compounds and has the potential to be used as a renewable chemical feedstock. Here we explore the thermochemical reactions of a-hydroxy phenethyl phenyl ether (a-HO-PPE), an important structural unit in lignin, at 345- 375 °C in a biphenyl solvent. The major pyrolysis products of this substituted PPE can be explained by the typical free radical chain mechanism described previously for PPE, however, initial results show additional new products where their origination can be described as coming from the following pathways; competitive C-C homolysis, a competing C-C phenyl shift as well as products from dehydration to form alkenes. We can explore the chemistry of the a-hydroxy PPE in comparison to the parent (PPE) and methyl derivative (a-MeO-PPE) to probe the intramolecular hydrogen-bonding, and through the use of DFT calculations we can explain key elementary reaction steps through individual rate constants and steady-state kinetic approximations for key hydrogen-transfer steps to define the products and selectivity. This new evidence shows the impact that substituents have on individual reaction steps and how essential it is to understand the reaction pathway mechanisms and kinetics that influence product formation and selectivity.