Radicals from the gas-phase pyrolysis of catechol. 2. Comparison of the pyrolysis of catechol and hydroquinone.

Formation of radicals from the pyrolysis of catechol (CT) and hydroquinone (HQ) over a temperature range of 350-900 °C was studied using low-temperature matrix isolation electron paramagnetic resonance (LTMI EPR) spectroscopy. Comparative analysis of the pyrolysis mechanisms of these isomeric compounds was performed, and the role of semiquinone-type carrier radicals was studied. Pathways of unimolecular decomposition of intermediate radicals and molecular products were identified from the examination of the potential energy surface of catechol calculated at B3LYP hybrid density functional theory and composite CBS-QB3 levels. The results were compared with the experimental observations and mechanistic pathways previously developed for the pyrolysis of hydroquinone.