Oxidation of Diphenylamine by OH Radicals and Excitation of the Diphenylamino and OH Adduct Radicals

Article abstract of DOI:10.1021/j100266a040

The primary product of the OH reaction with diphenylamine (DPAH) is a mixture of OH adducts (DPAH radical-OH) which subsequently eliminate OH^- ions via a pH-independent and an acid-catalyzed process.The rate constants of these two processes have been determined.The acidic amino radical cation (DPAH⁺ radical) thus obtained has a pK_a of 4.2.The adduct, the amino radical cation, and the neutral amino radical (DPA radical) were excited with frequency-doubled ruby laser pulses (347 nm).The excited state of the latter two amino radicals are shorter lived than the presently utilized laser pulse.Furthermore, no laser-induced shift in the acid-base equilibrium of DPAH⁺ radical/DPA radical could be observed.This lack of laser excitation effect leads to the conclusion that the difference in acid-base equilibrium constants (ΔpK_a^*) of the ground vs. the excited state is substantially smaller in the radical than in the analogous singlet states of the parent amine molecule.Foerster cycle considerations based on the absorption spectra of the two forms of the radical substantiate this conclusion.Excitation of the OH adduct leads to OH(1-) elimination from the excited state.This elimination leads to production of the amino radical cation in its ground state.Relaxation of this laser-induced perturbation of the acid-base equilibrium to its thermal value provides an independent method to measure the rates of equilibration.