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

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