HOMOLYTIC BOND DISSOCIATION ENERGIES IN LIGNIN MODEL COMPOUNDS. β-O-4 AND α-O-4 ETHERS

In designing industrial processes for lignin conversion into fuels or useful chemicals, it is important to understand and be able to control the chemical pathways by which such chemical conversions occur. Careful estimates of bond dissociation energies are critical in assessing these mechanistic preferences and the use of heats of formation of both lignin model compounds and their radical products has been central to this effort. A simple and accessible method for estimation of bond dissociation energies in lignin model compounds is proposed which is based on known values for heats of formation of appropriate free radicals and heats of formation for model molecules. These energies are in reasonable agreement with those obtained by more sophisticated procedures e.g. the methods of quantum chemistry. The introduction of substituents both in aromatic nuclei and in α-position of a side chain causes only a small deviation (ca 20 kJ mol-1) in Cα-Cβ bond dissociation energy.