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

Abstract

The kinetics of the death of phenoxy radicals In• 2,6-diisobornyl-4-methylphenol (DBP) and2,6-ditretbutyl-4-methylphenol (ionol) in toluene at 295 K is studied by EPR. The first-order effective rateconstants 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 thephenoxy radicals of DBP are dimerized with the formation of the p-C,O-dimer, while In• ionol predominantlyforms the p,p-C,C-dimer. The dimers are in reversible equilibrium with phenoxy radicals, while theirreversible consumption of In• occurs in the reaction of their disproportionation. Based on the density functionaltheory (DFT) research and published data, it was found that the value kef = k/2K of DBP is higher dueto the much higher disproportionation rate constant of In•, although the equilibrium constant K of thereversible dimerization of the phenoxy radicals of DBP is also higher than the equilibrium constant for In•ionol.