STUDY OF SPECTRAL CHARACTERISTICS, KINETICS, AND EQUILIBRIA OF RADICALS DERIVED FROM HYDROXY BENZOPHENONES

Studies on radical equilibria and the spectral evaluation have been carried out for three monohydroxy-substituted benzophenones (HOBP's) in aqueous solution. The transient ketyl or anion radicals were generated via hydrated electron (eaq-) reaction or dimethyl ketyl radical reaction in a pulse radiolysis experiment. The reactivity of both the undissociated (HOBP) as well as dissociated (-OBP) forms toward these reducing agents were studied. eaq- was found to react with the HOBP's and -OBP's with diffusion-controlled rates which are of the order 3 × 1010 dm3 mol-1 s-1. In the case of the para derivative, two acid−base equilibria were identified (pKa 9 and 11) in the pH range 6−13, one corresponding to the protonation−deprotonation at the OH site of the ketyl radical and the other for the protonation−deprotonation at the carbonyl site. For the ortho derivative, the intramolecularly hydrogen bonded structure of the radical anion has been found to be stable even in strongly alkaline solution (pH 13). Three di...