Pulse radiolysis study of some radical protonation reactions

Abstract

The rates of establishment of the acid-base equilibria for the radical anions of benzaldehyde, benzamide, benzonitrile, benzophenone, p-cyanoacetophenone and fluorenone have been studied by pulse radiolysis. In each case a first order rate of reaction was observed with kobs = k'+k"[H+], the constants having values of k' = (0.3-7.8) x lo4 s-' and k" = (0.7-2.5) x 1O'O dm3 mol-l s-'. These rate constants are associated with the reaction of the radical anion with water (k') and H+ (k"). The nature of the radical ions involved is discussed.' G . Beck, Dissertation (TU Berlin, 1968).

Mechanisms of action and reactivities of the free radicals of inhibitors

“…The following results have been obtained at room temperature: k2 -1.2 X 1010 M^-s"1 and k3 =* 7.8 X 104 s-1 for benzophenone radical anion (BP*-) in water containing 2.5 M fert-butyl alcohol. 205 The rather high values k2 ~1010 M^-s"1 and k3 = 5 X 109-10u M^-s"1 indicate that the acid-base equilibrium is established very rapidly. Linear correlations have been found between the pK& of radicals and the Hammett and Taft constants,28 redox potentials of ketones, aldehydes, and quinones (for ketyl and semiquinone radicals),198,206 and the difference in the rr-electronic energies of the acid and basic forms of conjugated radicals.207 There is promise in the quantum-chemical calculation of radical affinity for proton (PA).…”

“…The rates of protonation of benzophenone and pcyanoacetophenone radical anions were measured in ref 205 with the aid of the pulsed radiolysis technique. The radical anions decayed via reactions 7-2 and 7-3.…”