Arrhenius Parameters for Reaction of the tert-Butylperoxy and 2-Ethyl-2-propylperoxy Radicals with some Nonhindered Phenols, Aromatic Amines, and Thiophenols

Abstract

Preexponential factors and activation energies are reported for the transfer of a hydrogen atom from phenol, β-naphthol, aniline, β-naphthylamine, thiophenol, and β-naphthalenethiol to a tertiary alkylperoxy radical ((CH₃)₃COO^• and C₂H₅C(CH₃)₂OO^•). The A-factors fall in the range 2 × 10⁴ to 2 × 10⁷ M⁻¹ s⁻¹ and increase in the order C₆H₅SH ~ β-C₁₀H₇SH ~ β-C₁₀H₇NH₂ < C₆H₅NH₂ ~ β-C₁₀H₇OH < C₆H₅OH while the activation energies fall in the range 1 to 5 kcal mol⁻¹ and increase in the order C₆H₅SH ~ β-C₁₀H₇SH < β-C₁₀H₇NH₂ ~ β-C₁₀H₇OH < C₆H₅OH ~ C₆H₅NH₂. Differences in activation energies and preexponential factors are not consistent with a reaction mechanism which attributes low activation parameters solely to an equilibrium between the reactants and a hydrogen bonded free radical – reactant complex, followed by H-atom transfer within the complex.