Isatin halogen-derivatives redox behaviour

Abstract

Isatin halogen-derivatives like other isatin derivatives have several pharmacoterapeutic applications, such as antibacterial, antitubercular, and anticancer activities. The electrochemical behaviour, at a glassy carbon electrode, of some mono- and di- fluoro, chloro, bromo and iodo isatin derivatives, by cyclic, square wave and differential pulse voltammetry, over a wide pH range, was investigated, and compared with isatin electrochemical behaviour. The presence of one or two halogens in the benzene ring affected the oxidation processes. The oxidation mechanism of isatin monohalogen-derivatives, with only one halogen at the position C5 or C7, was an irreversible, pH-dependent, adsorption-controlled process, and occurred in three consecutive charge transfer reactions, first on the benzene ring with the production of one hydroxyl group attached to the ring, and the electroactive oxidation product formed was oxidized to para- and/or ortho-quinone derivatives and polymeric products. The isatin dihalogen-derivatives oxidation was also irreversible, in two consecutive charge transfer reactions, with the formation of polymeric products, and occurred at more positive potentials. The reduction mechanism of isatin halogen-derivatives was a pH-dependent two consecutive charge transfer reactions. The first process was the reversible reduction of the carbon-halogen bond and the second the irreversible cleavage of the carbonyl group at the position C3 in the heterocyclic ring. The halogens substituents in the isatin benzene ring gave rise to different redox processes, depending on the number and halogen position.