The Benzylperoxyl Radical as a Source of Hydroxyl and Phenyl Radicals

• Published in: Chemistry : a European journal Vol. 20; no. 40; pp. 12917 - 12923
• Main Authors: Sander, Wolfram, Roy, Saonli, Bravo-Rodriguez, Kenny, Grote, Dirk, Sanchez-Garcia, Elsa
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 26-09-2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Chemistry; Combustion; density functional calculations; Infrared radiation; matrix isolation; Oxidation; Phenyls; Photolysis; QM/MM calculations; radical reactions; Radicals; Spectroscopy; Toluene; QM/MM calculations; oxidation; radical reactions; density functional calculations; matrix isolation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201402459

The benzyl radical (1) is a key intermediate in the combustion and tropospheric oxidation of toluene. Because of its relevance, the reaction of 1 with molecular oxygen was investigated by matrix‐isolation IR and EPR spectroscopy as well as computational methods. The primary reaction product of 1 and O2 is the benzylperoxyl radical (2), which exists in several conformers that can easily interconvert even at cryogenic temperatures. Photolysis of radical 2 at 365 nm results in a formal [1,3]‐H migration and subsequent cleavage of the OO bond to produce a hydrogen‐bonded complex between the hydroxyl radical and benzaldehyde (4). Prolonged photolysis produces the benzoyl radical (5) and water, which finally yield the phenyl radical (7), CO, and H2O. Thus, via a sequence of exothermic reactions 1 is transformed into radicals of even higher reactivity, such as OH and 7. Our results have implications for the development of models for the highly complicated process of combustion of aromatic compounds.
Getting reactive: The benzyl radical is a key intermediate in the tropospheric oxidation and combustion of toluene. The reaction of the benzyl radical with molecular oxygen, which was investigated by matrix‐isolation IR and EPR spectroscopy as well as theoretical calculations, leads via the benzylperoxyl radical (see figure) to the formation of species with even higher reactivity, such as the OH radical and the phenyl radical.