Self-termination rate of para-substituted benzyl radicals in aqueous solutions: a time-resolved study

The self-termination rates of the benzyl radical (C₆H₅CH₂^{{radical dot}}) and para-substituted benzyl radicals (XC₆H₄CH₂^{{radical dot}}) were studied in aqueous solutions. The Arrhenius parameters and activation energies were determined in the temperature range 275.5-328 K. The kinetic activation energies of these radicals were close to the dynamic activation energy of the solvent, indicating that the termination rate is controlled by diffusion. The values for the rate constants (2k_t (10⁹ dm³ mol^-1 s^-1)) and the activation energies (E (kJ mol^-1)) were 5.94±0.52 and 14.69±0.61 for CH₃OC₆H₄CH₂^{{radical dot}}, 4.52±0.2 and 17.65±1.16 for CH₃7z.sbnd;C₆H₄CH₂^{{radi cal dot}}, 3.07±0.45 and 17.58±0.97 for HC₆H₄CH₂^{{radical dot}}, 4.13±0.81 and 19.10±1.20 for ClC₆H₄CH₂^{{radical dot}} and 4.17±0.44 and 14.62±0.52 for NO₂C₆H₄CH₂^{{radical dot}}.