Aqueous chlorination of acebutolol: kinetics, transformation by-products, and mechanism

This study investigated the reaction kinetics and the transformation by-products of acebutolol during aqueous chlorination. Acebutolol is one of the commonly used beta-blockers for the treatment of cardiovascular diseases. It has been frequently detected in the aquatic environment. In the kinetics study, the second-order rate constant for the reaction between acebutolol and chlorine (k (app)) was determined at 25 +/- 0.1 A degrees C. The degradation of acebutolol by free available chlorine was highly pH dependence. When the pH increased from 6 to 8, it was found that the k (app) for the reaction between acebutolol and free available chlorine was increased from 1.68 to 11.2 M-1 min(-1). By comparing with the reported k (app) values, the reactivity of acebutolol toward free available chlorine was found to be higher than atenolol and metoprolol but lower than nadolol and propranolol. Characterization of the transformation by-products formed during the chlorination of acebutolol was carried out using liquid chromatography-quadrupole time-of-flight high-resolution mass spectrometry. Seven major transformation by-products were identified. These transformation by-products were mainly formed through dealkylation, hydroxylation, chlorination, and oxidation reactions.