Pulse-radiolytic investigations of catechols and catecholamines. 3. Adrenalone.

Transient spectra, decay kinetics, rate constants with hydroxyl radicals (OH) and superoxide anions (O2 -), and the identity of unstable intermediates are reported for adrenalone. They were obtained after pulse radiolysis in various oxidizing and reducing aqueous systems. Both rate constants for the reaction with ·OH and O2 - of 1.0 × 1010 and 2.3 × 107 M-1 s-1, respectively, are quite high. In the case of ·OH attack several products could be separated by high-pressure liquid chromatography whereas with O2 - no stable products are formed. A mechanism is put forward, proposing formation of both o- and p-semiquinones after water elimination from the initial ·OH adduct, and respectively, the reversible formation of o-semiquinone in systems containing O2 -. Reduction by eaq -, the rate depending on the pH, resulted in the formation of the ketyl radical. Even though this species decays by A second-order process, we were unable to detect the putative dismutation product adrenaline. Side-chain cleavage to form 3,4-dihydroxyacetophenone and methylamine occurs in alkaline solutions