Comparative Analysis of the Kinetics and Mechanism of the Decay of Phenoxy Radicals of 2,6-Diisobornyl-4-Methylphenol and 2,6-Ditret-Butyl-4-Methylphenol

The kinetics of the decay of phenoxy radicals In center dot 2,6-diisobornyl-4-methylphenol (DBP) and 2,6-ditretbutyl-4-methylphenol (ionol) in toluene at 295 K is studied by ESR. The first-order effective rate constants of the decay of In center dot are determined: kef = 0.30 s(-1) (I) and 8.4 x 10(-3) s(-1) for DBP and ionol, respectively. Using the density functional theory, the mechanism of the decay of In center dot is analyzed. It is found that the phenoxy radicals of DBP are dimerized with the formation of the p-C,O-dimer, while In center dot ionol predominantly forms the p,p-C,C-dimer. The dimers are in reversible equilibrium with phenoxy radicals, while the irreversible consumption of In center dot occurs in the reaction of their disproportionation. Based on the density functional theory (DFT) research and published data, it was found that the value k(ef) = k/2K of DBP is higher due to the much higher disproportionation rate constant of In center dot, although the equilibrium constant K of the reversible dimerization of the phenoxy radicals of DBP is also higher than the equilibrium constant for In center dot ionol.