Free radical chemistry of atenolol and propranolol investigated by pulse and gamma radiolysis

Using pulse- and γ-radiolysis the free radical chemistry of atenolol and propranolol was investigated in aqueous solutions evaluating also the consequences of radical reactions on the elimination of organic content and toxicity. In aerated solutions, the hydroxyl radicals (•OH) induce the degradation; at low dissolved O2 concentration, the hydrated electrons (eaq−) may also contribute to the reactions. Propranolol showed higher reactivity towards both •OH and eaq− than atenolol. About 80–90% of •OH attack occurred on the aromatic rings (benzene or naphthalene), the reactions on the oxypropanolamine side chains had lower rate. The reactions with the aromatic rings gave hydroxycyclohexadienyl radicals, by radical titration experiments α-aminoalkyl and aminium radicals were shown forming by •OH attack on the side chain. Only the end-products of propranolol showed toxicity at low doses which was attributed to the formation of naphthalene derivatives, e.g., substituted naphthols.