High-energy ionizing radiation-induced degradation of amodiaquine in dilute aqueous solution: radical reactions and kinetics

Abstract

The widely used antimalarial drug amodiaquine (AQ) contains a 7-Cl-quinoline unit, a substituted 4-aminophenol part connected through the amino group and a tertiary amine part. The 4-aminophenol unit can be easily oxidized through radical intermediates to iminoquinone. This reaction also takes place in vitro and in vivo enzymatic reactions. The reaction is expected to have an important role in degradation of AQ in surface waters and also during degradation in advanced oxidation processes. In this paper by means of radiation chemical techniques the one-electron oxidation and reduction of AQ were studied using transient kinetics, kinetics of AQ degradation, formation and decay of end-products of radical reactions. The hydroxyl radicals were shown to add both to the quinoline (∼ 38%) and aminophenol (∼ 50%) parts via formation of hydroxycyclohexadienyl radicals and by H-abstraction or by an electron removal from the tertiary amine part of the molecule (∼ 12%). The dihydroxycyclohexadienyl radical formed on the aminophenol part is suggested to transform to aminophenoxy radical. The hydrated electrons can also effectively contribute to AQ degradation. Chemical oxygen demand and total organic carbon content investigations were also made in order to characterize the ionizing radiation-induced oxidation and mineralization. In aerated 0.1 mmol dm−3 solution, at 2.5 kGy absorbed dose AQ and its higher molecular mass degradation products demolished completely. Ionizing irradiation is a capable technique for degradation of AQ under both oxidative and reductive circumstances.