Hydroxymethyl cyclohexadienyl peroxy radical

In the case of toluene, as shown in Reaction Scheme 7.10, three reaction pathways of hydroxymethyl cyclohexadienyl radical with O2 are conceived the formation of (1) cresol (B) by the H-atom abstraction from the OH-added carbon (pathway a), (2) toluene 1,2-epoxide (C) and the 2-methyl oxepin (D) equilibrated with it, and (3) hydroxymethyl cyclohexadienyl peroxy radical (E) formed by the O2 addition to the benzene ring (Suh et al. 2003 Cartas-Rosado and Castro 2007 Baltaretu et al. 2009). The formation of cresol by pathway (a) is well known, and o-cresol is produced predominantly followed by p- and m-cresol reflecting the ortho- and para-orientation of the OH addition to benzene ring (see Sect. 5.2.10). However, the ratio of the H-atom abstraction from the benzene ring of hydroxy... 

The formation of hydroxymethyl cyclohexadienyl peroxy radical (E) by pathway (c) in Reaction Scheme 7.10 is thought to be the most important as a process to produce ring-opened compounds, which are well known reaction products of OH and aromatic hydrocarbons. The O2 addition reaction to the OH-added benzene ring radical is reversible, and in the case of benzene, the equilibrium constant and the enthalpy change is given as K(298 K) = (8.0 0.6) x 10 ° cm molecule" (Johnson et al. 2002), and = ( 44 2) kJ mol (Grebenkin and Krasnoperov 2004) for the hydroxycyclohexadienyl radical. Therefore, hydroxycyclohexadienyl radicals formed in pathway (c) are in general stable in the atmosphere, and play an important role as intermediates in the oxidation reactiOTi of aromatic compounds. 

Two reaction pathways to form ring-opened compounds in the oxidation reaction of toluene and OH are thought to occur, one through hydroxymethyl cyclohexadienyl peroxy radical (E) and the other through toluene-1,2-epoxide (C) or 2-metyl oxepin (D) in Reaction Scheme 7.10. Reaction Scheme 7.11 summarizes former pathways for peroxy radical (E) shown in Reaction Scheme in 7.10 based on recent findings. 

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