Reaction Dynamics of Excited Ketoprofen with Triethylamine

The reaction dynamics of ketoprofen (KP) with and without triethylamine (TEA) in methanol both in the ground and the excited states was studied by laser flash photolysis and the pump−probe emission spectroscopy. After the excitation, triplet KP abstracted a hydrogen atom from methanol to form KP ketyl radical (KPH). In the presence of TEA, the acid−base equilibrium state was found to be KP + TEA ⇄ KP- + TEAH+ in the ground state. The equilibrium constant was determined to be 32 ± 7. Excited KP- rapidly underwent decarboxylation to form a carbanion resonant with the 3-ethylbenzophenone ketyl biradical anion (3-EBP-), followed by a proton-transfer reaction with TEAH+ to produce the 3-ethylbenzophenone ketyl biradical (3-EBPH). Furthermore, 3-EBPH was found to make a complex with TEA, whose equilibrium constant was obtained to be 18 ± 2 M-1. The complex formation ability of 3-EBPH was discussed compared with benzophenone ketyl radical (BPH).