Arrhenius Parameters for Reaction of tert-Butylperoxy Radicals with some Hindered Phenols and Aromatic Amines

Abstract

The reaction of tert-butylperoxy radicals with some 2,6-di-tert-butyl-4-substituted phenols, α-naphthol, α-naphthylamine, and N-phenyl-α-naphthylamine has been studied by following the change in radical concentration with time using an e.p.r. spectrometer. Rates of radical decay were first-order in both reactants and were not influenced by the presence of tert-butyl hydroperoxideAbsolute values of the second-order rate constants were measured from −35 to −100° and the preexponential factors and activation energies fell in the range 104–105 M−1 s−1 and 0.5–1.0 kcal mol−1. Rate constants for deuterated phenols (OD) and aromatic amines (ND) were an order of magnitude lower than for the corresponding light compoundsThere was no evidence for quantum mechanical tunneling in these hydrogen atom transfer reactions and it would appear that the activation parameters are low because reaction initially involves the formation of a hydrogen bonded peroxy radical – phenol (or aromatic amine) complex, followed by the transfer of a hydrogen atom within the complex